Not a stuck open thermostat.

[adallak]

 Hello everyone! Long time no see. Old members might remember me. 

     I always check the engine temperature through the dashboard during long highway trips. It's always been 176-181⁰F. 

      Suddenly, it surprised me with 165⁰. I have not done anything to the engine, cooling, etc. I opened the hood and the radiator upper hose was soft. I could squeeze it easily. I opened the coolant cap with a little hiss if any (with engine idling). I'm not losing coolant.

       I suspected a stuck open thermostat and covered almost entire radiator front surface with a piece of cardboard. That brought the temp. to 179⁰.

       ASSUMING that the original stat had failed, I have replaced it with another 180⁰ one. Guess what? The same 165⁰! The strange thing is that the same piece of cardboard now did almost nothing! Now, the temp. would not go up more than a couple of degrees. on a long highway drive 

       I realized that I did not even check the original stat during the replacement. Did check it today and it's perfectly closed. 

       This is an LT1 engine with fancy cooling system. Again, I am not loosing coolant. Please someone enlighten me because I am at a loss.  

[Bruce Nunnally]

is it possible the radiator fans are coming on too soon, or  running on high all the time?

[adallak]

2 minutes ago, Bruce Nunnally said:

is it possible the radiator fans are coming on too soon, or  running on high all the time?

Hi Bruce! Nope, the fans are fine, acting as they should. 

[cdgrinci]

Perhaps a bad temp sensor?  Your thermostat has tested correctly so it should warm your engine to the set reading of, pretty close to, 180.

[adallak]

23 minutes ago, cdgrinci said:

Perhaps a bad temp sensor?  Your thermostat has tested correctly so it should warm your engine to the set reading of, pretty close to, 180.

Unfortunately, I do not have an infrared thermometer to veryfy the actual temperature, but something tells me the sensor is fine. If the reading was wrong and actual temp. was about 180, the system would be pressurized, the upper hose would be hot and stiff, and opening the coolant reservoir cap woulld  be a catastrophy. Would not it? 

[BodybyFisher]

Hi Armen, I got your PM.  I initially felt that your stat was open till I read this thread.   I tend to agree with cdgrinci, I would pull the connector off the engine temp sensor and check its resistance.  If the sensor resistance drifted it would be reported wrong to the PCM and the PCM would report the temp wrong to you.  Even a little corrosion on the contacts could increase resistance.  If you have the service manual the resistance number should be in there, get your ohm meter out and test it at the proper temp shown in the manual.  Also test it at operating temp.  Mike

Hello everyone I hope all are doing fine.  I am eying an XTS/CTS coupe, so I may be back one day soon.  

[adallak]

Thank you, gentlemen. Checking out the sensors never hurts. I wish the one associated with the diagnostics display were easy to get to. I'll update if I find out something. 

[Göran W]

Hi BbF. Don´t be a stranger!

[BodybyFisher]

3 hours ago, Göran W said:

Hi BbF. Don´t be a stranger!

Hello Göran, I am currently driving a Jeep Library and it's painful need to get a Cadillac asap.  I have become an F1 racing fan and am thrilled Cadillac is planning to get involved.  I better stop by more, the system has me tagged as a rookie 😉🤣 , thanks

This sounds awesome >>

 

 

[BodybyFisher]

3 hours ago, adallak said:

Thank you, gentlemen. Checking out the sensors never hurts. I wish the one associated with the diagnostics display were easy to get to. I'll update if I find out something. 

The coolant temperature sensor is hard to get to?   It wouldn't need to drift much to throw you off 10-15 degrees. That small of a drift might be below the threshold to set a code.  I am not sure if increased resistance from corrosion would increase or decrease the indicated temperature maybe the service manual would provide some idea.  

I can't imagine anything else that would cause a legitimate drop in temperature, so it has to be a false reading.

[rockfangd]

Welcome Back.

I suggest replacing the coolant temp sensor. I say this in reading the original thread and replies that followed. Hot and cold swings over time, bumps and bangs, etc... can have an effect on a sensors ability to be accurate. Ie resistance value slightly off. Do not go with aftermarket if at all possible. I have not had good luck with them being accurate

[adallak]

21 hours ago, BodybyFisher said:

The coolant temperature sensor is hard to get to?   It wouldn't need to drift much to throw you off 10-15 degrees. That small of a drift might be below the threshold to set a code.  I am not sure if increased resistance from corrosion would increase or decrease the indicated temperature maybe the service manual would provide some idea.  

I can't imagine anything else that would cause a legitimate drop in temperature, so it has to be a false reading.

The LT1 has two such sensors. The one on the block is relatively hard to get to, but it seems to be connected to the idiot light. The other one is easily accessible. I'll experiment a bit more. Often you replace the original part only to realize it was actually better than the replacement. ))

Just another sign the sensor is fine - the heat I get through the vents is something rather related to 167 deg than 180deg. That's for sure. The upper radiatot hose feels colder as well. I am not at home to play with boiling the stats and checking their actual opening temperatures, unfortunately. 

On 4.9 engine you could watch sharp drop of the coolant temperature when the thermostat opened. This engine is different - no drop at all. It is almost impossible to tell when the thermostat opens. 

[BodybyFisher]

Yea, I hear ya, but you replaced the thermostat with a 180.  A 180° stat begins to open at 180°.  If you are getting 167, the stat should not be open, causing the temp to continue to climb.  Are you sure it doesn't take a 190° and not 180° stat and the old one was hanging open?

One other thing could be possible, is a locked fan clutch in combination with the cool ambient temps.   This might be supported by your temps increasing when you blocked radiator air flow.

So it seems that you feel that your temp is actually low based on heater output and the upper radiator hose.  You are in Massachusetts?

[adallak]

6 minutes ago, BodybyFisher said:

Yea, I hear ya, but you replaced the thermostat with a 180.  If you are getting 167, the stat should only be partially open, causing the temp to continue to climb.  Are you sure it doesn't take a 190° and not 180° stat and the old one was hanging open?

So it seems that you feel that your temp is actually low based on heater output and the upper radiator hose.  You are in Massachusetts?

Yes, Mike, the OEM is 180 deg and yes it really feels like rather 167 than 180. That's one the reasons I am reluctant to replace anything. Every time you touch something on this 28-years-old girl, you break something! Just imagin still playing with your 1994 DeVille! LOL. Yes, in Mass. 

[BodybyFisher]

I just edited my comment reread it regarding the fan clutch

[adallak]

The fans are fine, they turn on as they supposed to do if I let the temperatures climb. The cardboard is on the other side of the radiator. 

[BodybyFisher]

3 hours ago, adallak said:

The fans are fine, they turn on as they supposed to do if I let the temperatures climb. The cardboard is on the other side of the radiator. 

Ok, so you don't have a fan clutch.  You have electric fans.  Are they turning on 100%, because of a fault in say the AC compressor?  Some faults cause the fans to default on when they shouldn't be on at all for safety.   Can you pull codes? 

[rockfangd]

There is not a whole lot that should cause it to run cool. Hot maybe, but not cool. I agree about not wanting to touch what might not be broke. Scratching my head here. Maybe the engine is self cooling lol. Have to think some more on this one

[sonjaab]

I would replace the 165 thermo. with a 180.

Or whatever is the act. required thermo?

• I have had cool heat issues with my 93.

Changin core didnt work.

New 180 thermo and bang!

Cheap and easy..........

These new junks aint running in the mfr. required range the computer goes nuts!

 

[adallak]

40 minutes ago, sonjaab said:

Sonjjab, 

It is a 180 stat or at least that's what I have ordered. 

 

 

[adallak]

13 hours ago, BodybyFisher said:

Ok, so you don't have a fan clutch.  You have electric fans.  Are they turning on 100%, because of a fault in say the AC compressor?  Some faults cause the fans to default on when they shouldn't be on at all for safety.   Can you pull codes? 

Mike, the AC has been deleted by me years ago. The fans act based on the temperatus from PCM and they do properly. Nope, fan do not run during trips at all. 

Coukd air in the system create all this chaos? I do not know how air would get into the system since I have done nothing to it. Will bleed it in a few days. Bleeding an LT! is a mess just like the entire cooling system I never liked. 

[adallak]

13 hours ago, rockfangd said:

There is not a whole lot that should cause it to run cool. Hot maybe, but not cool. I agree about not wanting to touch what might not be broke. Scratching my head here. Maybe the engine is self cooling lol. Have to think some more on this one

The only thing I may suggest is that the new thermostat is not really 180. It came with that Jiggle Pin Weep Hole and was made in Israel. Never saw a part made in Israel before. 

[BodybyFisher]

Yea the easiest thing to do would be to buy an ac Delco thermostat to eliminate that possibility.   

Air in the system will cause bad heat and overheating if anything.  

[rockfangd]

I completely agree on the delco tstat. The quality of so many things has been so bad that words cannot describe, and what's worse is nobody seems to care. I have been trying to find and use old stock whenever I can

[adallak]

Thank you, gentlemen. I'll update if/when I find the problem. Nice to be  back to the board.