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My Overheating problem...


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If you want to make sure, have a cooling system pressure test done or buy a cooling system pressure tester, that will alert you to leaks

Fans work

Stat replaced

Cap is suspect

Purge line now clear

Water pump belt slipping, tensioner applying pressure?, not determined

No obvious leaks

Coolant concentration appears good at least 50/50

Coolant smell in tank?, not determined

Cold start roughness?, seems to be a yes

Heater putting out hot or cold air since purge line cleared, not determined

Good luck let us know how this turns out

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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Did you ever get a block test kit and run the test as suggested in post #3? That would have answered the question about 10 days ago.

I agree Ranger, I said the same thing, smell the tank for exhaust fumes and test the coolant for by products, but ImaCad said this

"As stated earlier in the thread, I'm pretty sure a bad head gasket is part of the problem. I'm just trying to sum up everything else that's not working, then go from there"

Given that the PURGE LINE was proven to be clogged and is now clear, a test of the coolant is in order, given the temp spikes

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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Did you ever get a block test kit and run the test as suggested in post #3? That would have answered the question about 10 days ago.

I agree Ranger, I said the same thing, smell the tank for exhaust fumes and test the coolant for by products, but ImaCad said this

"As stated earlier in the thread, I'm pretty sure a bad head gasket is part of the problem. I'm just trying to sum up everything else that's not working, then go from there"

Given that the PURGE LINE was proven to be clogged and is now clear, a test of the coolant is in order, given the temp spikes

Correct. I'm already quite sure head gasket issues are part of the problem. I'm just trying to take all other coolant system issues off the table so I know what I'm dealing with. Up until recently, the car ran decent without any disabling problems. That changed, and I'm just trying to sort out any other coolant system issues that are at play. thx, je

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Doing a combustion byproduct test a week ago would have told you if you even "NEEDED" to "SORT OUT" any other issues...

Had a mechanic tell me 5 months ago he suspected that a bad head gasket was the principal cause of coolant loss and subsequent over-heating. Cutting back on the miles driven seemed to be keeping the "fatal flaw" in check, without any real issues, other than adding a pint of coolant every hundred miles. It was the quantum leap in over heating that spurred me to put these questions out there.

I already determined the bolt with a hole in it was plugged. Don't know if a combustion byproduct test would have told me that. I know that the heater still doesn't work, indicating a plug or an air bubble, and I don't know if a combustion byproduct test would have indicated that either.

Yes, I'm probably trying to saddle a dead horse here, but it still seems the radical over-heating bump could be coming from elsewhere.

So if you will all indulge me, here's the latest...

Been driving the car around town a few times lately, and here's what seems odd:

*The car does not overheat under tow or duress. In fact, the car runs around 203 at steady speeds of 45mph. Driving up hills does not cause a temp spike.

*At stop lights or slow downs, the temp increases rather quickly. As I pull away, it drops back down again.

*If the car appears to be heading towards over-heating at a stop, I can slip it into neutral and rev the engine to about 1200 rpm, and the temp begins to drop. I do not have to be moving (with air passing through the radiator) for the higher rpms to lower the temperature.

Other problems aside, what would you guys think about this scenario by itself? My first impulse is that the water pump or the tensioner is bad. At idle, it simply won't keep up, but at modest driving rpms, the car runs at near normal temps.

I'm still a bit baffled, because most the feedback I've seen here, indicates the temp spikes with a bad HG occur under acceleration or going up long hills. That is not what's happening here.

So, any final feed back you have is appreciated. After this, I'll probably give the car (and you guys) a rest!

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On the heater problem...

Either the heater core is stopped up or the climate control system is not letting water flow thru it.

On the overheating...

What is your idle speed?

What is the outside temperature?

Is the AC on?

"IF" the AC is on, are the fans running?

Have you checked the belt and tensioner??

The belt may be slipping at low RPM.

I seriously doubt that it is a water pump.

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On the heater problem...

Either the heater core is stopped up or the climate control system is not letting water flow thru it.

On the overheating...

What is your idle speed? 650rpm

What is the outside temperature?between 50-60 degrees on latest drives

Is the AC on? Auto Econ, so no the AC wasn't actually engaged

"IF" the AC is on, are the fans running? During other phases of testing the car at idle, I've heard/seen the fans come on between 220-230

Have you checked the belt and tensioner?? As a "non-mechanic", I would have to ask "what should I check for?" The belt does spin and looks OK

The belt may be slipping at low RPM. Crossing my fingers that this is the culprit. But is it the tensioner or the belt that needs replaced?

I seriously doubt that it is a water pump. Roger that

As a sidebar, I tried a "burp" method the other day, that called for letting the engine idle with the heater on for 30+ minutes with the cap off. After about 20 minutes the exit hose from the heater (as judged from a diagram on another thread) began to warm. Inside the car, the heater began to function somewhat, but not up to par. After about 45 minutes of idling, with the surge tank rising and lowering and the heater making a comeback, I turned the car off. Later on, I was back to having no heat again. So it appeared at the time that the heater problem might be air bubble related, as I eventually began to get some flow. But then, it did not maintain later. I should add that the temp during this test with the cap off was a steady 228. Fans were running. I attribute the rather high idle temp to the uncapped system.

Other people have suggested a couple of 3-4k rpm bursts with the cap off as an air bubble purge. Haven't tried that yet. thx, je

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On the heater problem...

Either the heater core is stopped up or the climate control system is not letting water flow thru it.

On the overheating...

What is your idle speed? 650rpm

What is the outside temperature?between 50-60 degrees on latest drives

Is the AC on? Auto Econ, so no the AC wasn't actually engaged

"IF" the AC is on, are the fans running? During other phases of testing the car at idle, I've heard/seen the fans come on between 220-230

That is normal.

Have you checked the belt and tensioner?? As a "non-mechanic", I would have to ask "what should I check for?" The belt does spin and looks OK

If you take the belt off... you can turn the tensioner by hand to check for a binding bearing or excessive play / wobble in the tensioner. At that time you can inspect the belt for glazing and cracks.

The belt may be slipping at low RPM. Crossing my fingers that this is the culprit. But is it the tensioner or the belt that needs replaced?

The spring in the tensioner may be getting weak and not holding sufficient pressure against the belt to insure that it is turning properly at low RPM...

"IF" you replace the tensioner... replace the belt also... just as a maintainence measure.

I seriously doubt that it is a water pump. Roger that

As a sidebar, I tried a "burp" method the other day, that called for letting the engine idle with the heater on for 30+ minutes with the cap off.

After about 20 minutes the exit hose from the heater (as judged from a diagram on another thread) began to warm. Inside the car, the heater began to function somewhat, but not up to par.

That kinda indicates that the heater core is clogged up.

After about 45 minutes of idling, with the surge tank rising and lowering and the heater making a comeback,

I turned the car off. Later on, I was back to having no heat again.

The level in the tank will vary according to the engine temp and whether of not the thermostat is open or closed.

So it appeared at the time that the heater problem might be air bubble related, as I eventually began to get some flow. But then, it did not maintain later.

I suppose it is possible, but I have never heard of an air pocket in the heater of a Cadillac causing that.

The only vehicle I know of that has that issue is a Nissan Altima. On the Altima, you have to elevate the front of the car and let it idle and do some other stuff to make it purge the air from the system.

On a Cadillac... the line going into the surge tank purges the air from the system.

I should add that the temp during this test with the cap off was a steady 228. Fans were running. I attribute the rather high idle temp to the uncapped system.

That is normal.

Other people have suggested a couple of 3-4k rpm bursts with the cap off as an air bubble purge. Haven't tried that yet. thx, je

My feeling about that is that it would blow most of the coolant out of the system and cause more problems than it fixed.

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The heater problem is related to

1) a clogged heater core

2) low coolant

3) low coolant as a result of a clogged purge line, that does not allow the system to be filled with coolant

4) gunk in the coolant tank clogging the heater circuit but that is not likely, but it may be clogged because someone put the cooling supplement in the tank instead of the upper hose

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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*The car does not overheat under tow or duress. In fact, the car runs around 203 at steady speeds of 45mph. Driving up hills does not cause a temp spike.

*At stop lights or slow downs, the temp increases rather quickly. As I pull away, it drops back down again.

*If the car appears to be heading towards over-heating at a stop, I can slip it into neutral and rev the engine to about 1200 rpm, and the temp begins to drop. I do not have to be moving (with air passing through the radiator) for the higher rpms to lower the temperature.

This does not sounds like a HG problem.

As a sidebar, I tried a "burp" method the other day, that called for letting the engine idle with the heater on for 30+ minutes with the cap off. After about 20 minutes the exit hose from the heater (as judged from a diagram on another thread) began to warm. Inside the car, the heater began to function somewhat, but not up to par. After about 45 minutes of idling, with the surge tank rising and lowering and the heater making a comeback, I turned the car off. Later on, I was back to having no heat again. So it appeared at the time that the heater problem might be air bubble related, as I eventually began to get some flow. But then, it did not maintain later. I should add that the temp during this test with the cap off was a steady 228. Fans were running. I attribute the rather high idle temp to the uncapped system.

No need to go through all that. If the purge line is clear, the engine is self purging. Revving it to 3K or just a few drive cycles will purge any air in the system. Check the purge line and flush the heater core. The sealant tab residue that GM used is known to clog both which will cause both overheating and loss of cabin heat.

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Finally did a coolant system pressure test. Have to say I was a bit surprised by the results.

I did both the cold pressure pump test, and the idle test to observe build up pressures.

On the cold test, I pumped the system up to 15psi, and watched the needle. I could not detect any drop off on the needle in the two minute test cycle recommended by the manufacturer. I continued to leave the pump on the surge tank for another 4-5 minutes, but did not see the needle move at all. Did not observe any leaks in the engine compartment, and nothing leaking into the cabin.

I then did the start up test, with the pump at zero.

It took about 12-13 minutes for the car to get up to the 195 degree range. At that point, the psi on the gauge was 4. Due to whatever the problem really is, I expected the idle temp to rise, and it did. At about 212 the psi was 5. At about 220, the psi rose to 6. The fans kicked in, but would not moderate the temperature. At 230, the psi was 7, and at 238 the psi was between 7 and 8. I shut the car off at that point. This test was about 20-25 minutes.

Per the manufacturer, head gasket problems would have been indicated by a quick increase beyond normal psi of 7. This never occurred. If there was no spike on the needle, the manufacturer advised to look for the needle fluctuating or quivering, indicating issues with the problem cylinder on a potential head gasket breach. This never happened either.

Now I don't know if the cold test on the Northstar requires you leave the system under pressure for long periods, but the car passed per manufacturer directions. It also passed engine idle test.

Do you think I need to go further on the head gasket test?

Given the situation, my plan is to take the car in for professional flush, a back flush of the heater core, and a test/replacement of the belt and tensioner on the water pump.

Whaddya think?

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I think these are good results.

What is the status of your radiator?, new/old? Could the radiator be clogged and not flowing?

I think your plan sounds good, let us know how this goes

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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There is one more test you can do, to check the head gaskets

You need to create an adapter from a spark plug with a fitting on it to fit an air compressor fitting. Screw the fitting into the cylinder on the compression stroke and pressurize the cylinder to 100 PSI, and see if it holds and listen at the tank for bubbles and air.

I hope you find a radiator flow problem. Did you test the coolant for combustion by products? Refresh this thread, the purge line flows good?

By the way, we had a member experience overheating as a result of an exhaust restriction, Ill try to find the thread

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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I think these are good results.

What is the status of your radiator?, new/old? Could the radiator be clogged and not flowing?

I think your plan sounds good, let us know how this goes

The radiator has not been replaced by me, and I'm not sure the previous owner did so in his pursuit of the over-heating problems.

Given the engine's ability to cool under higher rpms, I'm thinking along the lines of the belt tensioner. It would seem to make sense that a slipping water pump belt wouldn't keep up at idle, but keep up (within limits) at higher rpms. I've read elsewhere that the tensioners pretty much give up the fight after 12-13 years, and 175k.

Will keep you posted.

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There is one more test you can do, to check the head gaskets

You need to create an adapter from a spark plug with a fitting on it to fit an air compressor fitting. Screw the fitting into the cylinder on the compression stroke and pressurize the cylinder to 100 PSI, and see if it holds and listen at the tank for bubbles and air.

I hope you find a radiator flow problem. Did you test the coolant for combustion by products? Refresh this thread, the purge line flows good? Did not do a combustion by products test. On the purge line, my most recent test showed little or no flow at idle. Checked the bolt, it was clear. Hosed out the line with both ends disconnected. Started the car up again, and again saw little flow at idle. I revved the engine, and the line spurted coolant. I took this as another indicator of belt slippage on the water pump. Little flow at idle, with a spurt after revving up

By the way, we had a member experience overheating as a result of an exhaust restriction, Ill try to find the thread

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We have always been told that a bad water pump belt or tensioner would create problems at highway speeds

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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It is very easy to check the belt tensioner. Use a 1/4" breaker bar in the square hole in the tensioner assembly and work it back and forth. If it moves easily, the tensioner is usually OK. As a side note, the tensioner bearing may be on its way out.

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

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I read the whole post best I could went out to my 97 and checked my surge tank and the hose routing.

Coolant flows into the surge tank and out through the tanks lower hose to the heater and from there to the water pump housing. I'm fairly certain the problem is the heater core.

The surge line fills the tank but the heater core is blocked and the coolant in the tank boils out the overflow. Bypass the core or replace it. Like one member said someone put stop leak in the surge tank.

Maybe sometimes head gaskets get the blame and its really the heater I cant imagine how many times pellets were added to the surge tank causing overheating resulting in gasket failure.Mike

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The heater being clogged will NOT cause overheating, that is straight from the guru.

Look at the actual heater pipe diagram, you will notice that the hose from the tank is T'd into the DOWNSTREAM side of the heater core, heading toward the water pump, coolant WILL FLOW out of the tank if the core is clogged.

See this

NSCoolingSystemCircuit.jpg

and this:

NSHeaterHoses.jpg

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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You can see the T in this photo from when I replaced my heater pipes on my 96

CrossoverJob034.jpg

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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I read the whole post best I could went out to my 97 and checked my surge tank and the hose routing.

Coolant flows into the surge tank and out through the tanks lower hose to the heater and from there to the water pump housing. I'm fairly certain the problem is the heater core.

The surge line fills the tank but the heater core is blocked and the coolant in the tank boils out the overflow. Bypass the core or replace it. Like one member said someone put stop leak in the surge tank.

Maybe sometimes head gaskets get the blame and its really the heater I cant imagine how many times pellets were added to the surge tank causing overheating resulting in gasket failure.Mike

The heater core being clogged will NOT cause overheating or a head gasket problem, see above.

(it was a good theory though)

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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If you run into any jams post and we'll come back

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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If you run into any jams post and we'll come back

As it stands now, I'm going to take the car in for a heater core back flush and the best coolant system flush I can find. Don't know how much variation there is in coolant flushes. I will then test the car, and if need be, move on to the belt and tensioner on the water pump. Hopefully, the riddle will be solved by that point.

thanks for all the input!!

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You can flush your heater core till it runs clear with a water hose.

Don't forget to check the purge line to see if it flows.

If you want PM me and Ill forward you my cell phone number

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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