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questions on northstar operating temps and fan temps


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Hi everyone, I read the forum posts on northstar overheating, but couldn't find a specific answer to my question:

I just bought my first northstar, a 1995 seville sts. I got it for a good price so I couldn't pass it up.

I"m used to working on foreign cars, and my new caddy is confusing me.

On my VW Jetta for example, the coolant goes from cold to 190 degrees and stays there cold / hot / whatever happens.

On my northstar, the coolant goes past 190, it's about 210 on the highway (90 degree day), and coming off the highway indicates around 225. Is this the normal operating range for this engine? What is the normal operating temperature range?

Also, the radiator fans work when the AC is on, but not when it is off. Does anyone know what temp the radiator fan is supposed to come on at? The previous owner said that the relay was bad, but I need to know what temp they operate on before I start electrical troubleshooting

any help appreciated :)

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I may have found my answer on another forum. Can anyone verify this:

"The thermostat is set to begin opening at 188 and fully open at 206. Unless the HVAC system is in AUTO, when fans run in slow all the time (A/C function commanded ON) the fans are controlled by the engine coolant temperature sensor and come on in SLOW at 224 and FAST at 236. The car should run, on the highway, at about 196-204. With the HVAC OFF, the temp will go to 224 in traffic, fans come on, and the temp goes down to 213 when fans turn off. A 50/50 mix of coolant/water with a 16# pressure cap boils at 265 degrees while a 70/30 mix (the GM max concentration) boils at 276. Fans do not run above 45 mph. (They're not needed then.) About 255 is the Northstar "overheat" warning point. Camel mode engages at around 270."

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It sounds like your cooling system is acting normal

Highway temps should range between 195 and 205

Local driving in the summer will run 212 to 217, traffic bumper to bumper in the summer will run 217 to 235 depending upon the outside temps

Here is info from the Factory Service Manual on the cooling fan operation. When the AC is on, the fans are commanded to LOW speed operation, with the AC off, the fans are off until the temp reaches 229, when the temp drops to 216 the fans will go off (unless the AC is on)... The fans do not kick into high speed operation till 234

The PCM will command fan operation when:

  • Low Speed Fan Operation
    • Engine coolant temperature exceeds approximately 106°C (229°F).
    • Transmission fluid temperature exceeds 150°C (302°F).
    • A/C operation is requested.
    • After the vehicle is shut OFF if the coolant temperature at key-off is more than 151°C (304°F) and system voltage was more than 12 volts. The fans will stay ON for approximately 3 minutes.

The fans will switch from low to OFF when the coolant drops below 102°C (216°F).

  • High Speed Fan Operation
    • Engine coolant temperature reaches 112°C (234°F).
    • Transmission temperature is more than 151°C (304°F).
    • When certain DTCs set.

The fans will switch from high to low (except DTCs set) when the coolant drops below 106°C (229°F).

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Thanks! Exactly the help I was looking for.

I expected it to be a little lower on the highway, but if 215 is normal for 70 mph on a hot day then I'm not in too bad of shape.

I was freaking out because of my prior experience, I didn't know the northstar operates normally on what I'd consider to be over-heating temps. I guess being all-aluminum you don't get the expansion issues of iron block / aluminum head engines?

I'll troubleshoot from here, the temp gauge seems to be working well so it shouldn't be hard to see if everything is ok.

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Glad to help, just make sure your system holds pressure, the purge line flows free, the water pump belt and tensioner are good, the cap is good, and when you drain and refill use at least 50/50 to 60/40 coolant concentration and use the cooling supplement tablets. Personally, I use distilled water to mix my coolant, get it at the grocery store in gallon jugs. Just drain and refill, do not flush it with a water hose, you introduce minerals and you then have pure water in the engine and its hard to balance the coolant concentration.

DO NOT use the commecial flush service that is out there for your cooling system or your tranny. If this car is new to you a drain/refill, cap and thermostat change will give you a baseline starting point.

The 95 used GREEN coolant, stick to the 2 year/24K miles change interval and use the tablets. If your heat is weak, backflush your heater core.

Welcome aboard

Pre-1995 - DTC codes OBD1  >>

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215 at 70 is acceptible on a HOT summer day, but we are talking 90 degrees PLUS. It should be in the 212 to 215 range, if you start seeing 217 at highway speeds in the summer that would concern me a bit.

Keep in mind that at 70 you are plowing a lot of air through the radiator, make sure the AC condenser and radiator fins are clean, by spraying water through them. Its a 95, parts could have been removed or blown off, make sure that all air dams, air deflectors are in place.

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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  • 2 weeks later...

Ok, so I drained and flushed the whole system, noticed that the coolant was kind of nasty when I changed it. I also noticed that the water pump tensioner pulley bearing was about shot, so I replaced that too. I also did the thermostat while I was there.

The car still runs hotter than I'd like.

I have a 1 hour drive to work, summer temps in the northeast have been 75-85 during my commute.

The engine starts cool (10 degrees hotter than the outside air temp sensor), quickly goes to 190 or so, then slowly climbs to around 200 on the interstate for the first 20 minutes. Then I get on some back roads and the temp climbs to 210-212 (still averaging 40 mph). The thing is it never cools down when I go faster, the car just keeps slowly building heat until it stabilizes around 225 degrees. On the way home the same thing happens (but quicker)

I can't solve this slow hour-long heat buildup to around 225.

I'm running radiator flush right now, so it actually starts to boil slightly when driving. I'm losing a tiny bit of coolant every day.

I think I have radiator issues / clogging. Thoughts?

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...

On my VW Jetta for example, the coolant goes from cold to 190 degrees and stays there cold / hot / whatever happens.

...

As I have heard (from the Cadillac Club Sweden part of this forum), most temp gauges in cars are dampened around the engine's normal operating temperature. This means that it looks like the temperature stays exactly the same, even though it fluctuates a bit. Only a larger difference would make the dial move. This is of course done only to give an illusion of an extremely stable system to the consumer.

...

The engine starts cool (10 degrees hotter than the outside air temp sensor), quickly goes to 190 or so, then slowly climbs to around 200 on the interstate for the first 20 minutes. Then I get on some back roads and the temp climbs to 210-212 (still averaging 40 mph). The thing is it never cools down when I go faster, the car just keeps slowly building heat until it stabilizes around 225 degrees. On the way home the same thing happens (but quicker)

I can't solve this slow hour-long heat buildup to around 225.

...

Does the engine start at 10 degrees hotter even when you leave it for longer times? In that case, at least one of your temperature sensors is off a bit.

Just to give you some idea of what is normal (at least for my engine): My '97 DeVille Northstar steady-states at 91°C (196°F). In hot weather it can go higher. It always climbs higher in heavy city driving after a while, when everything is warmed up. It does this whether it is 30°C (86°F) in the summer, or -20°C (-4°F) in the winter. If I go on the highway, and then exit and go slowly, the temperature rises. This is completely normal (even mentioned in the instruction booklet of my old '88 DeVille), and due to the fact that the engine has some heat left inside of it from the highway driving, and suddenly the cooling system is much less powerful (due to the lack of fast air flow). If I drive on the highway at say 60 mph, and then floor it into second gear up to 80 or so, the temperature usually drops about 3°C (5°F). I think this is due to the increased coolant flow from the higher rpm of the engine. After a while, it goes back to the steady-state temperature. In the same way, if I idle the car at e.g. 103°C (217°F) after some city driving after some highway driving (a good way to get the temps up), wait a while, and then push the gas lightly and shortly to spin up to about 1500 rmp or so and then down again, the temp sometimes drops a degree or two a few seconds afterwards, also because of the increased coolant flow. As far as I know, all of this is normal. The car never overheats, not even some years ago after a sloppy shop had forgotten to fasten the clamp of the lower radiator hose and I did not realize it until after I drove for two hours on the highway (I actually discovered it because I routinely checked the pressure of the upper radiator hose after work was done on the system, to see if it held the pressure after some hours of driving - obviously it did not). I fastened the clamp and filled up on coolant, and everything was fine. I have also driven the car close do Death Valley at 45°C (113°F). I was going around 60 mph, and the temperature of the engine was in the 100°C (212°F) range (a few degrees up or down - I don't remember exactly).

Btw: Engine heaters in either the upper or lower radiator hose does not work on these engines. The thermostat does not let anything flow into the engine, so only the hose gets heated. A block heater is needed (unless you have a later model - I think 2000-up, where there is a place for a contact heater on the outside of the engine).

Edited by hjb981
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Thanks for all the info; I had the same questions although I've owned my '99 Seville SLS for five years.

Questions: how do you measure your coolant temp so accurately? all I know is my gauge is normally straight up, noon. About 20% of the time lately it's been in the one o'clock position, and it never used to be: for almost all my 5 years of ownership it always stayed at noon; 'till recently.

No codes relating to cooling system (only the ubiquitous suspension codes; my struts have never been changed in 140K).

Coolant w/tabs was changed 10K ago.

So what will the first warning signs be if something is "slightly" wrong and overheating is about to happen? where will the gauge be pointing then, for instance??

thanks! Rick in Mexico City

"My worst day riding, is better than my best day working."

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Thanks for all the info; I had the same questions although I've owned my '99 Seville SLS for five years.

Questions: how do you measure your coolant temp so accurately? all I know is my gauge is normally straight up, noon. About 20% of the time lately it's been in the one o'clock position, and it never used to be: for almost all my 5 years of ownership it always stayed at noon; 'till recently.

No codes relating to cooling system (only the ubiquitous suspension codes; my struts have never been changed in 140K).

Coolant w/tabs was changed 10K ago.

So what will the first warning signs be if something is "slightly" wrong and overheating is about to happen? where will the gauge be pointing then, for instance??

thanks! Rick in Mexico City

I have the digital instrument cluster, which means that I can see the temperature digitally below my speedometer. It is one of the options that will cycle if I press the [information] button. You probably have two buttons instead of my [information] button, so that you can cycle both backwards and forwards, but maybe you will not get the temp reading if you have an analogue gauge anyway. I do not have an analogue temp gauge with a dial that points at all. I don't know if there is a way to see the exact temperature in your car, but it can probably be done in some kind of service mode - perhaps someone else can fill in here. But perhaps exact temperatures aren't that important - I just happen to get them that way. It would of course be good with a translation scale, so that when you say 1 o'clock position of the dial and I say xxx degrees, they can be compared. Either way, I think that you should read this thread:

http://caddyinfo.ipbhost.com/index.php?showtopic=32133

It should be very relevant to you.

Good luck from Jonas in Sweden :)

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Thanks for all the info; I had the same questions although I've owned my '99 Seville SLS for five years.

Questions: how do you measure your coolant temp so accurately?

Prior to your year model, it was possible to display a digital readout of coolant temperature. That capability was deleted from 1998 and later Sevilles.

....all I know is my gauge is normally straight up, noon. About 20% of the time lately it's been in the one o'clock position, and it never used to be:....

A change like that is worth paying attention to. It "could be" caused by a failing thermostat that is not responding to coolant temperature changes as intended. Thermostat replacement is not a difficult job; be sure to use OEM parts if you decide to do that replacement.

See the photo for approximate coolant temperatures for your year model; I say approximate because the temperatures were measured on my 1998 model with my thermostat and my temperature sensor. The parts production tolerances build up and can skew the values just a little.

So what will the first warning signs be if something is "slightly" wrong....

You have already noted a potential warning sign that "something" needs attention.

FWIW, I have no problem with coolant temperatures slightly higher than the atmospheric pressure vaporization point of water. Reaching that temperature ensures the nasty compression and other byproducts are removed from the crankcase oil.

th_Smallertempguagewithnumbers.jpg

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Ok, so I drained and flushed the whole system, noticed that the coolant was kind of nasty when I changed it. I also noticed that the water pump tensioner pulley bearing was about shot, so I replaced that too. I also did the thermostat while I was there.

The car still runs hotter than I'd like.

I have a 1 hour drive to work, summer temps in the northeast have been 75-85 during my commute.

The engine starts cool (10 degrees hotter than the outside air temp sensor), quickly goes to 190 or so, then slowly climbs to around 200 on the interstate for the first 20 minutes. Then I get on some back roads and the temp climbs to 210-212 (still averaging 40 mph). The thing is it never cools down when I go faster, the car just keeps slowly building heat until it stabilizes around 225 degrees. On the way home the same thing happens (but quicker)

I can't solve this slow hour-long heat buildup to around 225.

I'm running radiator flush right now, so it actually starts to boil slightly when driving. I'm losing a tiny bit of coolant every day.

I think I have radiator issues / clogging. Thoughts?

Hello , hru today ? If You have'nt figured it out yet , I would check the exhaust for the presence of coolant/moisture with the engine overwarmed as You describe . If there is coolant/moisture I would get the hose and slowly at first and with it still running spray the radiator and cool it down some , shut it off and let it cool down completely , then pull rocker/cam covers and check the head bolts for looseness . You may get lucky and be able to retighten or torque them to a point , being very careful (just a little at a time past say 30 or 40 lb/ft. You potentially could buy Yourself a year or two or more depending . I know this is not recommended , nor does it sound like it would work or be good but I've had vehicles that head bolts would loosen every few mo and was able to buy a year or year and a half and this vehicles head bolts would practically loosen themselves right out of the holes . Hopefully You're problem is/was something else , Good luck . Any questions don't hesitate

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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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Hello , hru today ? If You have'nt figured it out yet , I would check the exhaust for the presence of coolant/moisture with the engine overwarmed as You describe . If there is coolant/moisture I would get the hose and slowly at first and with it still running spray the radiator and cool it down some , shut it off and let it cool down completely , then pull rocker/cam covers and check the head bolts for looseness . You may get lucky and be able to retighten or torque them to a point , being very careful (just a little at a time past say 30 or 40 lb/ft. You potentially could buy Yourself a year or two or more depending . I know this is not recommended , nor does it sound like it would work or be good but I've had vehicles that head bolts would loosen every few mo and was able to buy a year or year and a half and this vehicles head bolts would practically loosen themselves right out of the holes . Hopefully You're problem is/was something else , Good luck . Any questions don't hesitate

If this method were to be used on an engine that had pulled the threads, the problem would reoccur soon, just like you mentioned. In the meantime, there could be a smaller leak. Perhaps that leak would lead to coolant in the oil, which would ruin bearings and other parts in the engine. That would make the problem much bigger. The car would also be rather unreliable during the time of waiting for the problem to reoccur. :blink::huh:

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Well said, its not that the bolts loosen, its that they PULL.. on the NS, tightening them is a useless exercise on a NS and could possibly make the problem worse, not that the pulled bolts are not bad enough

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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  • 4 weeks later...

Well, I think I finally solved the problem.

The car still runs slightly higher than I expect, but at least it cools down.

I was loosing a little coolant, I smelled it when I opened the hood but not in the exhaust. It seemed to be coming from the radiator. Also, the radiator didn't feel like it was getting as warm as it should. Long story short, I replaced the radiator.

The car now comes up to about 196-205 on highway driving, does about 212-215 during the slower portions of stop and go, and about 225 in traffic. It is however doing something it didn't before: cooling down. After stop and go or town driving, it goes right back to around 200 on the interstate. So far I don't appear to be losing coolant anymore either. I think I had a clogged and leaky radiator.

Interesting to note the effect engine RPM has on cooling. The Northstar is a big V8 that also revs high, that creates problems for a coolant pump design that flows well at low rpm and doesn't rob too much power / caviate / flow too fast at high rpm. I think cadillac designed the pump for higher rpm / lower power loss and it just doesn't circulate well at idle.

My next step is to change the temp sensor to eliminate what I think is a slightly-off gauge, but the system seems to be working much better overall now.

Edited by bikesandcars
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I am glad you figured out the problem, did you take the end tanks off to see if you were in fact clogged?

Regarding your statement that the water pump not circulating well at idle, consider this

1) I can let my NS idle all day long and it will not overheat, the fans will kick on and off, keeping the temp in a tight range, in the winter, it runs even cooler. While less coolant is circulated at idle compared to 3000 rpm, at idle the fans shed excess heat absorbed by the slower moving coolant.

2) Do not underestimate the RAM AIR effect of highway driving forcing cool air through the radiator, hell, the cooling fans themselves instantly lower the temperature when they kick on

3) With the AC off, the cooling fans will not kick on till 228 degrees, obviously GM does not see 228 degrees as an issue, and we can see 235 to 240 in summer traffic with no issues, with a cooling system that is in good condition. Realize that the NS has MANY places to loose pressure and coolant, many, and if a NS cooling system is NOT maintained properly, temps will be higher. My engine ran MUCH cooler when I replaced the crossover seals.

4) Your statement that cooling improves with RPM is true, the next time you are on the highway running 212 to 215, put your engine in 3, the RPMs will jump and your temp will drop.

The temps that a Northstar with a healthy cooling system ellicit are adequate according to a former member we had here who was a NS Powertrain engineer. It is the UNHEALTHY cooling systems like yours with its clogged radiator that are at risk.

One other thing you want to think about is your thermostat, use an AC DELCO and change it every couple of years.

The best thing I ever did to my 96 NS was to overhaul the coolaint system 100%.

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/

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Thanks for the feedback.

I checked for blockages, there were none. I've done the thermostat and given the system a good check so I believe for all intents and purposes I'm done (provided I don't discover another small leak somewhere).

My comments regarding cooling inefficiency are really just based on my opinion. I believe that in general the northstar cooling system is under-designed. Just because the engine will take operating temps of 190 to 240 on a regular basis doesn't mean that it is a good thing. I believe these engines would have a much better reputation if the cooling system wasn't designed so marginally. Thermal expansion plays havoc with mechanical systems, the engine as a whole would be more reliable if it stayed at 190 for all of its life (not to mention tolerances could be tighter).

In my opinion:

- The system should have enough coolant volume and radiator area so that it can remove all the heat the engine can generate all the time to keep 190

- The system should have a pump design that circulates fluid at an adequate rate from low to high rpm to ensure there is enough heat removal at low rpm.

I don't blame Northstar Engineers, I bet the business weenies stepped in and said cheapen the system.

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....I don't blame Northstar Engineers, I bet the business weenies stepped in and said cheapen the system.
The following four paragraphs are the words of one of those same engineers; maybe he can satisfy your doubts.

* * * * * * * * * * * * * * * * * * * * * * * *

It is desireable to get the coolant above 212 F so as to heat the

oil above 212 in city driving quickly so as to boil out moisture and

raw fuel that gets in the oil on cold starts. Running colder

thermostats is detrimental to engine life from this aspect,

particularily in colder climates and in short trip/urban driving

that doesn't heat the oil up otherwise.

The Northstar cooling system is a very sophisticated, high flow

system that is designed for a high output, high RPM, all aluminum

engine...not a system that was adapted from an older, slower

turning, cast iron, low output engine. The water pump on your 96

will pump around 105 gallons per minute at 6500 RPM (that is TWO 55

gallon drums in 60 seconds....think about it) while requiring a

minimum of power to do it. It is a very efficient water pump

impeller design that is designed to turn high RPM and move a lot of

water.

The main consideration of an all aluminum engine is NOT the absolute

coolant temps observed but maintaining thermal stability throughout

the engine. Keeping the hot spots cool and the cool spots hot

eliminates thermal fatigue of gaskets and seals and allows the

engine to "grow" and "shrink" with coolant temp changes as a single

entity...not dissimilar parts that stress the fasteners and gaskets.

This is accomplished by having VERY HIGH coolant flow rates thru the

block and heads constantly so as to maintain an even temperature

gradient across the engine regardless of the observed coolant temp.

Keeping in mind that the water pump can pump about 105 GPM at

6500.....only about 45 GPM is directed to the radiator. That is

sufficient for the heat rejection required and is the maximum that

is allowable for the long term life of the radiator....erosion of

the tubes, tanks, and end-tank oil coolers would result with more

flow. So....where does the other 60 GPM go....???....it is

recirculate back thru the block and heads in a re-circulation

loop....part of which is the heater core circuit which accounts for

about 7 GPM of flow at maximum engine RPM. The main part of the

recirculation circuit is the cast passages inside the water

crossover casting that the water pump resides in. When you remove

the stat you can see one of the coolant bypass passages at the end

of the thermostat mounting port...the large hole that the spring

loaded paddle covers.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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Thanks Jim, that is what was needed here

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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