92 Lesabre boiling coolant in the overflow reservoir

OptimistPrime

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I've got a problem with my 92 Lesabre, where it hesitates at full throttle and sometimes gives a check engine light. I popped the hood to look at it after a good long drive, and heard the curious sound of boiling water inside the overflow bottle. The coolant must be hotter than hell to make it boil like that. So now I'm trying to diagnose. The water pump is fairly new, and nothing is leaking. I'm thinking maybe the thermostat or coolant temp sensor. Has anyone experienced these issues before?
 

imidazol97

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What code do you get from the engine light. The early code system isn't as good as 95 on however...


Is the pressure cap good? Cleaned underneath to remove gunk with a toothbrush?

Is the radiator full when the car is cold?

Are the radiator fans working when the car is being driven? And are they
working if the AC is on? The radiator fans should kick on when the temperature gauge goes up?

What does the coolant look like? Orange and clean. Or brown and full of crud?

To check the thermostat requires a scanner a step above those that can only read codes. And may require a special cable to connect to the pre 95 cars...

Many inexpensive scanners can read the coolant temp.

Or try an infrared temperature "gun."

Are you using any coolant, that might indicate you've got a head gasket leaking. That gasket leak would continue to put exhaust into the coolant while the engine is running.

Determine if you're actually overheating, then you can start looking for why?
 
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Regal LTD Coupe

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Feel the hose on top of the rad going to the thermostat housing. If it feels ridiculously hot after the motor up, the thermostat isn't opening and the coolant therefore isn't cycling through the engine.
 

Homer Jay

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Could be the coolant mixture, check using a hydrometer tester.
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Thunderhawk09

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one of two common things one is just a thermostat stuck or two you have blown a head gasket seen this many times A, t stat stuck though would show up on temp gauge a blown head gasket you will see some loss of coolant from the radiator. The boiling is a sign that the compression is being lost on one or more cylinders and is blowing past head gasket back into the coolant system
 

OptimistPrime

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Thanks for the help, guys. The car isn't losing coolant, radiator is full when parked. The coolant is cruddy brown, so I'll be changing it next. I don't know what code it gives because I don't have an OBDI scanner. Temp warning light doesn't come on, but this model doesn't have a proper temp gauge with numbers. So I have no idea how hot I really am. The car drove fine on the way to work today, but started giving me fits on the way home. It seemed sluggish, similar to how it behaved when one of the coils went out, and when I opened the hood to check them, that's when I saw the boiling. Maybe they aren't sparking well enough and causing blow through due to compression loss, like Thunderhawk said. I will go drive it around and feel that hose like Regal said to do. I just replaced the rad cap, the other one looked pretty beat up.
 

OptimistPrime

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Oh, and I forgot to mention that the AC has never worked on this car. But god, how I wish it would.
 

2007LucerneCXL

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Just another item to consider if other things don't seem to be the solution is get a combustion leak tester. It can check the coolant for exhaust gases which would lead to a possible head gasket. But thermostat, coolant system flush and fresh coolant which was already mentioned, are simple next steps if they are past due.
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OptimistPrime

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After taking a drive, I felt that hose, and it was hotter than hell. I'll be putting a thermostat in next.
 

imidazol97

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The hose on top of the engine from the thermostat housing to the radiator is the exit route for coolant after the thermostat opens.

Let the engine cool completely. Start it and keep feeling that hose. It should be cool at first and as the engine warms you will start to feel some warm water move up the hose bleeding past the thermostat. But when the engine hits the thermostat opening temperature then that hose will become warm and keep warming as the flow rate from the thermostat increases.

The coolant cools as it goes down through the radiator to the lower hose. The lower hose goes to the water pump which sucks the coolant from the radiator back into the engine.
 

imidazol97

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Isn't this the era where two certain terminals on the assembly line diagnostic connector can be connected with a paperclip, and the check engine light flashes patterns to read out the numeric number for the error code. I believe it would flash a 1, pause then 2, and do that 3 times. Then it would flash the two-digit pattern for the error code 3 times, and at the end it would give the 1 and 2 code 3 times.
 

imidazol97

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Do you know if the coolant is the proper mixture, roughly 50 / 50? If it's actually more water, it will boil at a lower temperature than it's designed to operate at under pressure.

It would be great to have an infrared temperature gun to read the temps on the radiator from top to bottom.
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OptimistPrime

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Ok, after driving it around with the new thermostat I can see it still has the problem. Not quite as bad, but it's still there. The check engine light didn't come on, but it started hesitating after about 20 minutes of driving. That pipe on the top of the rad is still hotter than hell. I can see the fans spinning and the coolant mixture is a fresh 50/50 mix. It's a 180 thermostat, they didn't have a 160. Could that be the issue?
 

agaric

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Get a compression test to confirm whether you have a blown head gasket or not.
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Regal LTD Coupe

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The AC likely has no freon though one of the previous owners of my car who probably had it 20 years said he had to have the ECM replaced because the engine would just up and die on a hot day or the AC would just go out. Would start with the simple things though. Don't think head gasket issues are very common on the 3800.
 

Frampton

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The AC likely has no freon though one of the previous owners of my car who probably had it 20 years said he had to have the ECM replaced because the engine would just up and die on a hot day or the AC would just go out. Would start with the simple things though. Don't think head gasket issues are very common on the 3800.
Actually, head gaskets are quite common.
 

Regal LTD Coupe

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Actually, head gaskets are quite common.
Have owned three of them and never got that impression through various perusings over the years nor experience. Even when I thought the motor was a goner in my first one after changing the oil the first time and finding milkshake, the oil never looked like that again after any other oil change. Have never heard of the 3800 as anything other than about the most robust of motors to be obtained so to hear this claimed now is shocking and almost laughable to be honest, but sure there are exceptions to the rule. Maybe I've just been lucky but my words aren't solely anecdotal.
 

imidazol97

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The upper radiator hose should be hot after the engine has been running and the thermostat has opened. That's where the hot coolant goes on its way to the radiator to be cooled. Upper radiator hose should be at 195 deg. F. That is hot to the touch.

The car should have a 195 degree thermostat in it. Putting in a lower temp thermostat does nothing other than make the PCM work to compensate for the cold engine.
 
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