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99 Deville Northstar Overheat


truant

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Hi All,

99 Deville with Northstar 4.6L. 90,000 miles.

I am an Electrical Engineer.. meaning I've studied thermodynamics (heat transfer).

I've been fixing Caddy's (mostly broughams) and other cars, boats, bikes, diesels.. you name it for 18years. However, this is my first "modern" vehicle.

History:

September: Bought car for my wife. Enjoyed it through the winter.

Feb: leaking water pump. dealer replaced under warrantee.

March: Noted "check coolant level" on display. Added 50/50 dex cool.

April: Noted "check coolant level" on display. Added 50/50 dex cool. (Noted no visible leaks on car or ground)

Late April: Took to dealer (stalling) is under warrantee.

They found: sticking EGR valve.. replaced under warrantee. recommended intake cleaning (I did this myself).

May: Noted "check coolant level" on display. Added 50/50 dex cool (1/2 gallon each time).

May: Noted (to my shock) sudden loss of 2qts oil. (I run 10w30 mobil-one fully synth) Added 2 qts to bring back to full.

May: Noted loss of oil qrt #3. Added 1qrt.

May: Stalling again.. brought to dealer for what was I assumed a sooted EGR valve, and told them of coolant leaking and oil loss (I found weeping oil pan gasket).

They found: EGR sticking.

They also found "leaking coolant crossover pipe.. it's 5 hours labor.. your warrantee covers it."

Here's where it gets interesting.

I said "go for it, but I need the car for memorial day weekend travel (our other caddy is a 1990 brougham 225,000mile driver her to work cause she runs great, but no long trips vehicle).

They said "we can do it in time".. so that thursday morning they call me and say "opps the parts are not on the shelf.. we need to order them.. so come get your car, you can drive it because it's only a small leak and bring it back next week." I said "ok" and drove it away, packed it, and took off up the road.

At 80mph in heavy traffic the overheating began. At 250 or so I noticed the coolant temp (it was a hot day so I was watching it anyway). It kept going to 260, and auto shut my ac off.. (I switched to econ mode and 90F temp got some heat for a minute.. ). At this point I'm coasting in neutral with engine idle.. I finished coasting through a toll and it commanded engine hot / engine off, I lost my cabin heat at the same time, so I knew I was in trouble. I did as instructed, killed ignition and pulled over.

Called the dealership.. they told me it might be the thermostat.. so I pulled it out on the highway and refilled strait water. This got me home.. however she still overheated with no thermostat. The tech told me it was because there was no thermostat (which makes sense now.. the thermostat is a funny shaped one that plugs one hole in the engine (partially).

... I made it back at 55mph dropping to much slower on the hills.. still took three stops to add water to make it all the way.

Horrors begin: Noted as I pulled thermostat from the LOWER hose of the radiator that she poured GREEN antifreeze on the ground (sorry environmentalists.. I was stuck). I'm told (is this a myth) that GREEN + ORANGE antifreeze = GOO, or JELLO.

...

The Next Week: Took back to dealer and told them to repair. They replaced thermostat, fixed the coolant crossover pipe, super duper power flushed with a few extra solvants.. "road tested" and gave it back to me.

I gave it to my wife and she overheated on highway at 55 + hills.

I took it an nursed it home (just a few miles this time.

I gave it back to the dealer.. their tech spent all day with it and came up with "defective pressure cap". That was the most expensive pressure cap ever bought ($76).

.. needless to say.. that didn't work.

SO:

OK. Spent saturday afternoon with brother in law Mike at his place. We did a good flush with his garden hose, found everything open except for the air purge line. It was full of rusty muck. This is the "hollow bolt" referred to as being above the water pump. I cleaned this and was able to feel my screwdriver sticking through into the engine.

Discoveries:

The Northstar engine is flawed. The thermostat was placed on the cold water RETURN LINE from the radiator, instead of on the HOT WATER OUT of the engine (as on an old brute like the chevy 350). This design (intended I'm sure) prevents the engine from cooling itself quickly, and makes it terribly sensitive to any change in cooling system performance. This is undoubtedly necessary to prevent massive (rapid) changes in tolerance with the aluminum engine block.

We drilled holes in one thermostat and found that (with the use of two digital (+/-0.2 deg.F accurate, 1 second update) temperature probes INSIDE the upper and lower radiator hoses) that the thermostat opens and shuts itself very quickly. With a new (unmodified) thermostat I found that when the engine is at 230 degrees the thermostat can oscillate open and closed open and closed because the radiator fans are turned on at a higher speed and the return water is actually TOO COLD for the thermostat to remain open, so it shuts and the engine temp rises .. it opens the engine temp falls and it closes and repeat.

After 3 hours of micking with this and that We replaced the thermostat, went with an 18PSI pressure cap, and retested with strait water. The engine performed much better (we did all of our testing at idle or reving the engine). After much investigation, I decided I was content with the improved performance with the air-purge line now being open, so we refilled with 60% antifreeze (50% is OK, but 70% is the absolute best performance of the stuff) and drove it home (150miles).

On the highway at 80MPH in moderate traffic (2.5 people in car + tools and 10 gallons of extra water in trunk) I hit 260F once, .. what I noticed with my embedded temperature probes (inside both the radiator hoses, 2 inches from the engine) is that the thermostat stays at least partially open when just driving along.. this keeps engine temp at about 205 .. more or less where it should be. However, hit the power (not WOT, but just traffic negotiating on hills), the temp rises (three water pipes come together behind the thermostat to give it an indication of engine temp) then the thermostat opens more (as desired) but the rush of cold water into the engine causes it to close more than it should, or in some cases (when I hit 250 twice and 260 once) it fully closed.. this caused engine temp to skyrocket from 212 to 245 or higher before the slow moving thermostat could respond to it's error.

The thermostat opened just in time to save me from a boil off... of course I didn't let up on the car either.. I wanted to push it off the edge at this point.

My wife was uncomfortable with me performing WOT (wide open throttle) tests on the car (her neck) so I'm saving those for my homeward commute today.

I added between 1/2 and 1 gallon of 50/50 mix this morning before my trip to work (20miles) to completely top off the coolant tank.

Mike and I purchased a compression tester.. but didn't get a chance to use it. Sears sells a coolant system pressurizer... I might try that. Napa sells a combustion gases test kit (check your coolant) so i might try that.

Also I just realized that the orientation of the thermostat in its housing is very important to allow proper mixing of water from the three pipes that come together. I'm not sure how mine is oriented, because I didn't note that when I installed a new one (GM part, 180F opening as tested on stovetop in pan of water). But note that the backshell of the thermostat should be vertically oriented so that the spring and piston assembly is held only on top and bottom. I hope that's clear enough.. I can explain with a picture at some point.

My leaning is about 30% to sell.. 70% there's still hope. That will swing depending on if I can cook her on my way home today.

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Several things to inspect:

1) the condition of the water pump drive belt (could be stretched at 90,000+ miles)

2) the proper operation of the pump belt tensioner

3) the plumbing that clamps to the hollow bolt and connects to the top of the reservoir. If the bolt was clogged (and that was not rust) possibly the rubber hose is likewise. That line is an air purge line and it is very important.

Your cooling system was serviced improperly at some point if you found green antifreeze in there. I'll pass on redesigning the cooling system. But most modern engines use a very high coolant flow rate to avoid temperature gradients in the aluminum. About the only item that is a little unusual in the Northstar is the thermostat location.

Don't give up on it.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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The dealer said the coolant crossover pipe was leaking yet that was the only thing that wasn't replaced.... is it leaking or is the dealer just BSing you? If you have a leak, the system won't build pressure and will overheat. The Northstar engine needs to have the thermostat installed or all sorts of temperature issues will result. The fact that the return line to the surge tank was restricted may have everything to do with the overheating problem.

The orange and green coolants are compatable for just such emergencies - as long as you flushed it out, there shouldn't be a problem. Because someone installed green coolant in there, you will need to change the coolant every two years now as the silicates have plated the internals of the cooling system and they will deplete the corrosion inhibitors of the DexCool (orange coolant).

Check the oil level when the engine is hot - with 7.5 quarts in the sump, it will expand enough such that if you're topping ot off cold, it will be too full and the overfilled amount will quickly be consumed via the PCV system. The result is that the engine will appear to use oil. Synethetic oil is not required for your car - you can use it but the only difference you'll notice is your wallet will be lighter.

The Northstar is not a small block Chevy engine... It cannot be worked on as if it were or all sorts of trouble will result and then the mechanic will blame the engine rather than the improper repair technique" Your discovery that it is flawed because of the location of the thermostat could not be further from the truth... its location provides more even coolant temperature. The water pump flows coolant at the rate of 105 gallons per minute. Get rid of the 18psi cap and put the factory cap back on there or replace it with the correct pressure rating for the car. Stop attempting to redesign the cooling system and find the real problem.

Also you didn't state what type of coolant you used to refill the system but make sure that it is mixed 50/50 with distilled water. A higher concentration is not desireable - especially with DexCool.

Once you are to that point, then check the cooling system with a pressure tester to see where it is leaking.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Welcome to the forum.

This was a very detailed post. I am interested to hear your followup and resolution with the car. The embedded temperature probes are interesting, as I love more information, and fact-based analysis.

Bruce

2016 Cadillac ATS-V gray/black

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If there is a design flaw wouldn’t it manifest immediately even in brand new vehicles? Though we’re talking about a Northstar, this particular one is not related to the “Big Bang” so I don’t think it’s going to suddenly redesign itself after 90K miles. Since this overheating problem just started there must be a logical explanation; it just a matter of finding it. Not too long ago, there was a rather extensive thread in the topic of overheating. If you search, you should find it and perhaps it will help solve the problem.

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Thank you all for the fine feedback.

I read the chart on the dex-cool (that is all I have been adding, other than my home brew garden hose flush), and at 70% it raises the boiling point further than 50/50 and lowers the freezing point lower than 50/50. However, they always instruct 50/50 because it is very difficult to measure 70/30 and if you exceed 70/30 you'd might as well be running water because the boiling point will drop very quickly back to 212, and the freezing point will rise yet again to 32.

As for 15psi cap vs. 18psi cap. This is a 20% increase in system pressure. The hoses are easily rated for 100% overpressure.. but I do NOT recommend this technique for others with similar trouble to my own.

I put this cap on because

1. It installs much easier than the old cap

2. it has a pressure relief tab so I can play with the coolant system pressure under various temperature conditions (simulated pressure leaks etc).

3. The hoses are all new or nearly so and can take the extra beating for a short while.. until I get this all figured out.

As for redesign: I've thought about jerry rigging it, and placing an in-line thermostat in the hot water feed to the radiator. But two things stop me:

1. It worked just fine for 90,000 miles as someone mentioned.

2. I have a life.. or used to, and would not like to invest the time in a custom rig.

3. If it does turn out to be a striped head bolt and hence gasket and timesert required issue then I don't want any mods to wig out my warrantee co. (Also the reason I turned down my brother inlaw's offer of a K/N performance air filter).

However, as an engineer, just ask my wife.. I'll analyze this thing to mars and back.

We have a saying at my work (we design power supplies) "Test Everything!"

Air purge line:

I'm thinking that although I cleaned the bolt.. and tested the line from the bolt back to the engine by blowing with my lungs, and blew also to the expansion tank.. that it is possible more crapola can catch there. There is unfortunately a significant amount of rust in the system now, so that will need periodic cleaning.

I highly recommend that if someone reading this goes to change your own coolant, check these lines as well. They are easily accessible .. it'll take you 5 minutes, and maybe save you X*$1000.

Water pump is new.

Belt I can't say for sure.

Tensioner: I can see it jiggling while the engine is running..(at ilde) it jiggles in a repetitive pattern. I will specifically test the tension.. although i don't hear the belt slipping, so I would assume this is OK.

Keep the ideas coming.. I'm hoping to get to the bottom of this and make a good post for others to follow along with things NOT to do, and things to try.

Regards,

T

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Two things come to mind here. First off, it is most likely not rust you are seeing, but the cooling system suppliment tabs. They will give the coolant a rusty looking color.

Secondly, if you flushed the system with a garden hose, then drained it, you will only get about 2/3 of the water out (see my "Changed Coolant Today" post) thus diluting whatever mixture you put in.

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Distilled water only, now the cooling system is tainted with minerals and as Ranger said you have now created a problem balancing coolant concentration, but an engineer would have known that. The guru said NEVER to flush the system with tap water, DRAIN and REFILL.

Why not try to fix the problem first and not assume or conclude that the Northstar system is flawed? (on your first posting no less). Try take other people's suggestions and try not to shoot them down before actually taking a detailed look (water pump belt and tensioner). Do you really think you are sharper and better informed than the Powertain Engineers who designed the engine?

Keep in mind that the engine has been around since 1993 and it has matured and been improved. It has been validated and it is tested at full throttle for 300 hours and its tested in Phoenix proving grounds. If this engine was FLAWED, which it is not, I think it would have either be FOUND OUT, or CORRECTED since 1993.

In my neck of the woods this is a self-righteous approach to life and a great way to fail, engineer or not. The guru addressed the thermostat location in one of his posts when some other know-it-all commented on it, its a shame his posts are gone.

See Rollingthunders thread below, it was the by-pass bleeder line to the surge tank that was clogged like you found. Within this thread were many nay sayers and gloom and doomers, sound familiar?

http://caddyinfo.ipbhost.com/index.php?showtopic=5012&hl=

Glasses are half FULL in my world, not half EMPTY, I feel sorry for the people who believe that.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

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I appologise if I came off as a know it all. Freely admitted, I don't know it all.

1Cor 8:2 And if any man think that he knows any thing, he knows nothing yet as he ought to know.

I stand corrected.

Update: Belt tension tested OK, and the belt is new. The tensioner swings freely.

Since my first test drive (1st post) the temp has not risen above 232, so I'm tempted to think the air purge line was at least 90% of the problem.

Question: I think someone in a different thread mentioned that removing the rubber hose from the hollow bolt should cause water to "shoot out the bolt" while the engine is running. This would make sense to me, but I do not detect this condition (although I didn't take the hose off, I can pinch it with my fingers and I don't feel any fluid flow).

It would make some sense to me to have water always pouring out of this line so as to be continuously purging air from what otherwise appears to be the highest point of the cooling system other than the expansion tank. The water and any bubbles caught in it, would go over to the tank, the tank would catch the air rising out of the water stream and let the water drop back into the system. However I see no coolant flowing around inside the expansion tank either.. and I know there is at least some air in the upper radiator hose.

Comments?

I figured there was some coolant left in the engine, so I added strait dex-cool when I refilled. I haven't specifically tested the concentration, but someone told me if I could add.. what was it.. 1+ 5/8gallons of pure coolant I could get it to 50/50. I got a good bit more than that in.

Does anyone have a chart of the difference in temp with "tap water" and distilled water.

I was amazed to find I can actually get distilled water from wal-mart for $0.50/gal.

How do I purge the water from the lower end of the engine? Compressed air?

Also from my temperature measurements inside the lower and upper radiator hoses I suspect that the lower hose might colapse under high power bursts, especially if one catches it with the thermostat wide open. Either that or the hose is holding (I think mine feels just fine to a squeeze test, maybe I should check against a new one) and the coolant is bubbling in the hose from the pressure drop into the pump.

What I was seeing were repetitive changes in temperature from 100F to 175F in consecutive scans of the thermocouple (the temp probe). I thought perhaps that this was consistent with cavitation of some sort.. probe in water.. probe in air and back again. Because the thermostat can't move that quick, and the thermal mass of the radiator would make such swings in temp unlikely.

Would it be ok to say that older engines had ... shall we say "easier tolerances" and were less susceptible to percentage change degredations in cooling system performance.

After all, a single 3mm hole, 2" long can wipe out the whole cooling system for a 300Hp engine? Wow. Seems like an achilles heal to me.

Hey, since we're on it. Besides the rear suspension, is there any reason yall might know of that the deville (with the aformentioned 300Hp) can't tow more than a measley 1000lbs?

And what is the small 10"long 3" wide radiator out in front of the condensor? Is this engine oil cooling or transmission oil cooling?

T

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Since the reservoir is a relatively low-flow parallel path, I doubt if you will feel any water movement in the hose. In fact, pinching the hose would/should just stop the flow.

My flow test is to remove the hose at the reservoir end and check for flow in the entire length of that circuit (including the throttle body).

Not sure you will measure a significant difference in temperature or efficiency with distilled vs. tap water. But most of us that use distilled do so to avoid the (unknown) mineral content of tap water.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I appologise if I came off as a know it all. Freely admitted, I don't know it all.

1Cor 8:2 And if any man think that he knows any thing, he knows nothing yet as he ought to know.

I stand corrected.

T

No problem, sorry for calling you on it.

Understand that with this engine, you will need to do what all of us have had to do, leave MOST of our previous experience at the door, and relearn a hell of a lot. We can help you a lot, keep an open mind. Welcome aboard. Mike (Scotty/BodybyFisher)

This board carries the experience of a GM Powertrain engineer, that was directly involved with the development of the NS. When we refer to the GURU we are referring to him. His words, posts and experience are implanted into the minds of the members here, it may take time for it to come out sometimes as each of us has a part of him, but its there.

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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1) I still don't understaqnd how Green antifreeze got into the system. Looks like the dealer had the car for some time before this - didn't they notice the wrong coolant in the system?

2) did you add the cooling supplements (bars tablets) into the lower hose when you changed the coolant? if not, you need to.

3) was it rust or was it caked up tablets? in the line.

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I appologise if I came off as a know it all. Freely admitted, I don't know it all.

1Cor 8:2 And if any man think that he knows any thing, he knows nothing yet as he ought to know.

I stand corrected.

Update: Belt tension tested OK, and the belt is new. The tensioner swings freely.

Since my first test drive (1st post) the temp has not risen above 232, so I'm tempted to think the air purge line was at least 90% of the problem.

Question: I think someone in a different thread mentioned that removing the rubber hose from the hollow bolt should cause water to "shoot out the bolt" while the engine is running. This would make sense to me, but I do not detect this condition (although I didn't take the hose off, I can pinch it with my fingers and I don't feel any fluid flow).

It would make some sense to me to have water always pouring out of this line so as to be continuously purging air from what otherwise appears to be the highest point of the cooling system other than the expansion tank. The water and any bubbles caught in it, would go over to the tank, the tank would catch the air rising out of the water stream and let the water drop back into the system. However I see no coolant flowing around inside the expansion tank either.. and I know there is at least some air in the upper radiator hose.

Comments?

I figured there was some coolant left in the engine, so I added strait dex-cool when I refilled. I haven't specifically tested the concentration, but someone told me if I could add.. what was it.. 1+ 5/8gallons of pure coolant I could get it to 50/50. I got a good bit more than that in.

Does anyone have a chart of the difference in temp with "tap water" and distilled water.

I was amazed to find I can actually get distilled water from wal-mart for $0.50/gal.

How do I purge the water from the lower end of the engine? Compressed air?

Also from my temperature measurements inside the lower and upper radiator hoses I suspect that the lower hose might colapse under high power bursts, especially if one catches it with the thermostat wide open. Either that or the hose is holding (I think mine feels just fine to a squeeze test, maybe I should check against a new one) and the coolant is bubbling in the hose from the pressure drop into the pump.

What I was seeing were repetitive changes in temperature from 100F to 175F in consecutive scans of the thermocouple (the temp probe). I thought perhaps that this was consistent with cavitation of some sort.. probe in water.. probe in air and back again. Because the thermostat can't move that quick, and the thermal mass of the radiator would make such swings in temp unlikely.

Would it be ok to say that older engines had ... shall we say "easier tolerances" and were less susceptible to percentage change degredations in cooling system performance.

After all, a single 3mm hole, 2" long can wipe out the whole cooling system for a 300Hp engine? Wow. Seems like an achilles heal to me.

Hey, since we're on it. Besides the rear suspension, is there any reason yall might know of that the deville (with the aformentioned 300Hp) can't tow more than a measley 1000lbs?

And what is the small 10"long 3" wide radiator out in front of the condensor? Is this engine oil cooling or transmission oil cooling?

T

Disconnect the hose that leads from the water pump crossover to the surge tank at the surge tank fitting - it is on the lower portion of the surge tank. Have a helper start the car and coolant should pee out the hose. If it does not, the hose is restricted and will need to be cleaned. The surge tank is the high point of the system so any air will be purged out there. There are not any block drains so getting the engine totally purged will not be practical - that's why it is best to only drain and refill with coolant mixed 50/50. The exhause of a shop vac hose placed over the surge tank cap will help get more coolant out of the system. I removed the line on my '97 and it sprayed out.

The only reason distilled water is used is that it contains no minerals. You won't see any difference in temperature.

There is a spring in the lower radiator hose to prevent it from collapsing so unless someone removed it, I doubt that the hose is collapsing.

There was a problem somewhere in the cooling system on your car that was affecting its function. I wouldn't say tolerancing has much to do with it. If there is a restriction in a small block Chevy's cooling system, it will be affected too.

The 10x3" cooler in front of the A/C condenser is for the power steering fluid.

I don't know what you plan to tow but plan to tow a 2-place snowmobile trailer with my '97 STS - loaded, it weighs about 1500 lbs. I will install an auxiliary transmission oil cooler first though.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Question: I think someone in a different thread mentioned that removing the rubber hose from the hollow bolt should cause water to "shoot out the bolt" while the engine is running. This would make sense to me, but I do not detect this condition (although I didn't take the hose off, I can pinch it with my fingers and I don't feel any fluid flow).

It would make some sense to me to have water always pouring out of this line so as to be continuously purging air from what otherwise appears to be the highest point of the cooling system other than the expansion tank. The water and any bubbles caught in it, would go over to the tank, the tank would catch the air rising out of the water stream and let the water drop back into the system. However I see no coolant flowing around inside the expansion tank either.. and I know there is at least some air in the upper radiator hose.

Comments?

T

I don't think you will see coolant "shooting" out of the hose at idle. Maybe spitting is more like it. Raise the RPM and you should see a steady flow. Rev it high and it will "shoot". The temp changes and cavitation explanation makes sense. I'd pull the purge line at the tank and make sure you see some coolant coming out of it. The amout is irrelavent.

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I think the 'weak link' in towing heavier loads is not the 300 hp engine, but the tightly packaged automatic transmission tucked up under the engine where it is nice and hot anyway. The transmission is intelligently selected / capable for the weight of the car itself, but not for towing.

The RWD CTS is only rated for 1000 lbs also; I guess the Escalade is the way to go for heavy towing.

Bruce

2016 Cadillac ATS-V gray/black

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There are also no large structural members under the rear trunk area from which to attach a heavy duty hitch. These unibody cars just aren't set up for it.

Beware when towing more than the legal limit. Yes, that is a legal limit. Even though we think or know the vehicles can do more than that, if you get into an accident and the other lawyer has been through even 6 months of law school, he'll make you weigh your rig and if you're over, you up the creek. The GVW is the key (Gross Vehicle Weight). The weight of your car, loaded (with passengers/cargo/fuel), plus the weight of the trailer, cannot exceed the GVW. This is set using a number of factors, including cooling capacity, suspension/brake capacity, structural integrity, etc.

This very thread illustrates the ignorance we all have/had before learning the intracacies of the Northstar engine. Just as we were once ignorant to Northstar knowledge, we're just as ignorant about the towing capacity. If we're preaching to TRUST CADILLAC with the Northstar's cooling system, we outta also be preaching to TRUST CADILLAC when it gives a 1000 pound weight limit on these vehicles.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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I think the 'weak link' in towing heavier loads is not the 300 hp engine, but the tightly packaged automatic transmission tucked up under the engine where it is nice and hot anyway. The transmission is intelligently selected / capable for the weight of the car itself, but not for towing.

The RWD CTS is only rated for 1000 lbs also; I guess the Escalade is the way to go for heavy towing.

Bruce's comments caused some long gone old posts from "you know who" to come alive in my memory cells. Obviously, tranny fluid temperature needs to be controlled either with an auxiliary cooler or by avoiding the use of "D" and driving in "3" only (or both).

The tranny oil life monitor would pick up on any temperature excursions and count down the change interval accordingly.

Following the Owners Manual limits for towing is always recommended.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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:huh:

I rechecked the belt tension on the water pump, and played with the tensioner some more. Those are fine.

I replaced a section of the air purge line with a clear plastic tube so i could see what was happening there while the engine was running. (Note, don't try this at home with any regular hose.. use a high pressure hose else the pvc will get gooey at high temp and pop on you!!)

I see the coolant spitting from time to time towards the expansion tank, no continous flow.

However, removing the hose from the expansion tank end and blowing back towards the engine gives a clear hose.

Interesting quirk I've noticed, is that the level in the expansion tank doesn't seem to change, although I can detect that the upper radiator hose is basically empty (it's feeling like it is mostly full of air when I squeez it). I would expect that the expansion tank level would drop to purge the air out of the hose, even if this happened very slowly.

The car was doing well for me, then I gave it back to my wife. It overheated at 75mph, AC on full, outside air temp of 87F, moderate traffic moving steadily.

Since it boiled off everything.. two things must've been true. Less than 50/50 mix (although my sensors recorded max temp of 270F)

and the coolant must've been low.

I'm starting to suspect a restriction in the line between the expansion tank lower hose (a 1" hose) and the driver's side of the engine. GURU??

Since flushing and refilling the system (it isn't quite 50/50 this time.. I've got to drain and add more dexcool to get it there) I've done something new. I took one of my temperature probes, installed it into the lower hose, through the thermostat housing, THROUGH THE THERMOSTAT by way of the little brass tit that lets air bleed through when the stat is closed, and tied the end of the temperature probe around the thermostat housing. I'm hoping this doesn't backfire on me, because the pump could eat it if it were to break off.

This new sensor indicates a 174F temp most of the time.. but I've seen it as high as 224F if the engine is left to idle with no AC on. This tells me that the water is mixing well behind the stat and that cool water entering the engine is not really pushed over the thermostat piston (causing it to close), but instead sucked mostly into the pump.

An interesting observation is that water behind the thermostat can be a lower temperature than the computer's temperature sensor by as much as 20deg F in my measurements. However water in the UPPER radiator hose does not deviate more than a few degrees from the computer's reading.

I think the coolant behind the thermostat deviates from the computer's reading only when the coolant level is low.

My sensor in the lower hose before the water gets to the thermostat varies in temperature from 120F to 220F (220 only when engine idle, no AC so no fans) 120F doesn't happen a lot after the engine warms up. I mostly see 140 to 174F, with 165F being most typical for relaxed driving about the town (0-30mph, no AC).

At the sugestion of a co-worker, I added an overflow bottle, it gets about 1/4gal each time I run the car... the hose is under the water level so it sucks most of that back in.

Comments?

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I still think there is something with the purge line to the surge tank - it should pee out with the hose disconnected - not just spit coolant from time to time. I disconnected the purge line on my '97 when I bought it and just about received a DexCool shower. I had the line disconnected and the end was inserted into a margarine tub. There was a steady stream of coolant peeing out of the hose.

The dealer diagnosed the problem as a leaking coolant crossover pipe - was it replaced? The water pump was replaced in Feb. and the overheating started in May - it is possible that the water pump impeller has come loose from the pump shaft and is not circulating the coolant properly? It might make sense to pull the water pump and check it - it is easy to do provided you have the special socket. They can be purchased at any auto parts store. Remember that you turn the pump CLOCKWISE to remove it and COUNTERCLOCKWISE to install it.

Most of the chain stores will loan out cooling system pressure testers at no charge - pressure testing the cooling system will tell you a lot about what is happening.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I know you stated that the dealer replaced the cap for $76 but a couple of things caught my eye. A few things that you mentioned regarding the reservoir, 1) its not dropping even though the system 'stabilizes' and 2) you are boiling coolant out into a secondary catch bottle and 3) you seem to have air in the system.

Double check the cap to make sure its the correct cap, the correct cap has a poppet valve in the middle allowing coolant to enter as the engine cools but the valve is spring loaded and pulls up to seal, make sure its pulling up to seal. It sounds like you have air trapped in your cooling system, make sure that the bottom of the reservoir is not clogged or full of gunk clogging the bleed line.

I would pressure test the system also.

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Interesting quirk I've noticed, is that the level in the expansion tank doesn't seem to change, although I can detect that the upper radiator hose is basically empty (it's feeling like it is mostly full of air when I squeez it). I would expect that the expansion tank level would drop to purge the air out of the hose, even if this happened very slowly.

Having just changed coolant the other day, I can tell you for a fact that the coolant level in the surge tank should infact drop as the RPM's are increased, and rise again as they are reduced to idle, hence the term "surge" tank. It would seem that there is a blockage somewhere.

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Body by Fisher said it and I will ditto it. Pressure check the cooling system.

If the head gaskets are starting to go they will give the symptoms you describe. Since the failure is not a "blown out" gasket but a loss of tension (or pinholes) it will not act consistently. As the problem gets worse it will be obvious and more consistent.

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Hi

I rented a pressure tester, but I think it doesn't work right. I'm going to swap it for one at another parts store to check my results. (the needle drops a lb. or two at a time every 30seconds.. it looks beat up too).

With my clear hose right near the expansion tank on the air bleed line I do get a steady stream of water, especially if I rev the engine. However, I observed last night that at higher rpm's i get a nice foamy set of bubbles that NEVER STOPS, even after several hours of higher RPM. The level in my expansion tank doesn't change appreciably, but it does drop some when I rev up and rises fast when I let her fall back to idle.

Can anyone describe the smell of burning (combusted) anitfreeze to me? I think I'm going to take a lighter to some to figure that out. I get an interesting smell when I first start the engine in the morning with the exsaust.. not something I've smelt on other cars.. At first I thought it was some kind of emmisions thing.

Also, there are kits to check for combustion gasses in your antifreeze right?

Yes, the coolant crossover pipe was replaced. I can't see any coolant down in the crotch of the engine, not even steam.

Plan: Compression test saturday. If results indicate diffence in cyl. take to dealer .. tell them to fix under warantee. (I haven't done this until now, because they don't want to diagnose the head gaskets without charging me G's that I don't have.

I'd forgoten how much I enjoy working on cars (no sarcasm).

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The rise and fall of the coolant level in the tank sounds normal as does the foamy bubbles. Remember, the pump turns at the same RPM as the engine. At high RPM it is likely cavitating and pumping these small bubbles through the purge line. I have seen this on my daughters '99 when I changed coolant.

Smell a bottle of fresh coolant. Coolant from the exhaust will smell similar. Sort of a sweet smell.

Yes, they do make kits to test of combustion byproducts in the coolant.

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