I have a 1977 Grand Prix ... I am not a novice mechanic but this problem has me buffaloed...I have put a OEM 3 core radiator, water pump a 180 degree thermostat, new radiator hoses and new clutch fan also. The problem is when the car idles with a thermostat it runs hot very quickly. When the car is idling without a thermostat in it, it hits about 165 to 180 and goes no higher. No matter how long it idles. I've clean the radiator inside and out, doesn't seem to be stopped up. It start circulating fine when the temp hit 180 with the thermostat in it but keeps on going up to boilng. I don't have any white smoke coming out of the tail pipes, no oil on the dipstick or under the radiator cap. New radiator cap changed the plugs no water on them either. So what can cause a car to run fine without the thermostat and overheat with one. Also have checked the compression and all cylinder are compressing to 120. Any information would be appreciated

 

So is it a Camaro? Or a Firebird?

 

Thermostat installed backwards?

 

It's a 77 Grand Prix with a 400 small block engine.

 

The thermostat is installed correctly.

 

Sounds like a bad fan clutch to me. It’s slipping excessively, and not moving enough air.

 

Thank you for your reply Galaxie500..I forgot to put it in my post, but I did replace the clutch fan and yes it was slipping but it will take the hide off your finger now..

 

Ok, here is one more guess - wrong rotation water pump.

 

try putting in a good 180 degree thermostat from mr. gasket, and not the cheapy parts store ones, they look different and better built, I have had really good luck on 2 chevy 400 with them and both never got over 190 with mechanical fan and stock radiators, only other suggestion is to check your timing, if not advanced enough it will put extra heat into engine and exhaust system real quick if even a few degrees retarded.

 

...Mr NoEmissions84TA... I didn't know you could get one of those.. Didn't know they made them like that, but hey I'll check it and see...Thank you for the idea and reply... anyway to tell if it wrong without taking it off.

 

I will check the timing 2knight and see and get a better quality thermostat....It seems to work ok when it does hit 180 degree but it heats up so fast when I have it in like maybe 2 or 3 minutes and she's going up. which I know is not normal ... not that fast anyway. Like I said it take a good 7 to 10 of idling minutes to even get up to 165 with out it. I was leaning toward a head gasket but all or any of the symptoms of having one blown are not there... Thanks Mr 2knight for your response and answer.

 

No problem, I had a motor not advanced enough and the temperature rose really fast at a high speed idle, It was running only 5 minutes then overheated the headers which started the plug wires on fire, anyways lesson learned. I never knew timing made that much of a difference so something to check out for sure. How long has the problem persisted? or was anything changed before this problem started?

 

2knight I bought the car a couple months ago as a project car and it has been dong this way ever since I got it. Bout to drive me crazy not being able to fix it or findout what the problem is.

 

Gotcha so who knows what changes were made, I would check all 3, and all not too hard to do, check timing and keep in mind balancer may have slipped and be off, power time it where you advance it where it runs the strongest, back off timing if it pings when hot and accelerating or if it cranks hard when starting it after it's been drove, check the water pump, I don't know if you can identify reverse rotation by not taking it apart, maybe someone else can help with that, also change out for good mr. gasket thermostat, there made for high performance engines and more accurate opening temps. Don't give up on it should be a simple fix, is heater core hooked up? If not is there still a bypass hose running from water pump to intake?

 

Is this a Chevy 400 or a Pontiac 400?
What's the milage and condition of the engine?

What you are describing is impossible based on what you have told us. If the engine heats normally with no stat, then overheats like mad with a stat, then the stat is not opening, period. Mr gasket makes garbage and I don't care where it came from or what it looks like. I would start there, buy a quality stat from acdelco or equivalent and start over.

It's very unlikely its a reverse pump as it would always overheats, and that's a part for a Chevy motor not a Pontiac so depending what you have you can probably rule that right out.

Without the stat, can you drive the car without overheating?

And is the coolant boiling over into the overflow tank? How do you know for sure it's overheating? The factory gauges are never very accurate.

Does the radiator get hot or does it stay cold?

What radiator cap are you using and what is it's pressure rating?

 

I have to agree with everything that 86TA says, I was thinking those points as I was reading.

This is a super long shot - is the stat housing the correct one - could it be somehow contacting the stat enough to bend or deflect or limit the stat such that it would bind instead of opening? This is super unlikely but I am otherwise, as you say, buffaloed (I lol'd at the term) too.

 

86TA... I has 92,000 miles, It's a Pontiac 400 small block. It has a 16PSI radiator cap, Replace the temp sensor and gauge with a new one. The coolant is not boiling over into the reservoir. When it reads boiling, radiator does get hot and so do the top and bottom hoses. Thanks for your reply and advice.

 

Bow-Tied.. it has the original thermostat housing. I will take it out and check the temp in a pan of water with a thermometer in it also...Thanks for your reply and suggestions also.

 

So it doesn't sound like it's overheating. You say it reads boiling, what does that mean exactly? A factory gauge will probably read 220-240degrees as a normal operating temp and that's fine. Remember the coolant is under pressure and it's boiling point in much higher as a result. Just because it has a 180 stat doesn't mean it will always be able to maintain a true 180 degrees, it's just the temperature when it will start to open.

Does the car have the proper fan shroud installed, is the fan the correct distance from the radiator, and is the fan installed so it pulls air through the radiator not blowing towards it?

 

86TA... The car is as near all original as it can get as far as the engine components...It has the factory shroud and fan..I did change the clutch on the fan out and it was bad. The temp gets to 230 to 240 degrees on the gauge Only have drive it a short distant just to see how it was running and it ran fine... Would a laser temp check on the hoses help to determine if the gauge is reading correct or where should I check to get a true laser reading of the engine temp while its running? I never have used one of those. Thanks for your reply and help.

 

Ok thank you 2knight I will.. Thanks for your help and replies

 

An IR temp laser will give you an idea of what's going on, and it's a handy tool to have anyway.

I would take it for a longer drive and see what it does temperature wise. I don't think the car is overheating, but it's running warmer because it's not moving. The fan move a good amount of air but driveing at speed will move more air through the radiator.

These 3rd gen Camaro/firebirds supported by this website/fourm will have factory fan switches that don't even turn the fans on until 238 degrees from the factory for emmisions reasons.

So long as both hoses are hot and the upper hose is not swollen and ready to burst, everything seems fairly normal to me. It's also possible the cooling system may have a.little air trapped in it with can cause it to run a tad warmer. It will take some time for it all to work out. Just make sure the radiator cap is in good order and the overflow tank is vented.

 

Ok I will giver her a spin and see what happens and let you know ..Thanks again for your time and help.

 

I'm going back to the beginning to re-read this.
I just remembered a problem Ja85z28 had and am now wondering if it applies to your situation.


Edit: nope, not the same problem. Here was his: https://www.thirdgen.org/forums/cool...ml#post6131122


I still don't trust your thermostat. Do the pot of boiling water on the stove test.


Also, your thermostat will only work if it is submerged in coolant. If your top hose is full of air, the thermostat has not opened, or not opened yet. Squeeze that hose to try to push any air out. You should see bubbles in your overflow tank when doing so, and when you release, coolant from the bottle will be sucked in to replace that air. Your overflow bottle is there and operational, right?

 

NoEmissions84TA...I will check on the hose but they are brand new but will check them and make sure they're not collapsing..I am goin to do the boiling water test today and burp the engine and see if that helps...Also gonna check the timing and make sure that isn't off either. Thanks for your time and reply..

 

While your thermostat is out, drill one 1/8" hole in the flange.
This helps with eliminating any trapped air.

 

Thanks NoEmissions84TA, I've never heard of that but will try it.

 

Most modern stats have small crimped spots around the perimeter that will allow air to bleed past. If not, sure drill a couple small holes.

 

 

NoEmissions84TA...I checked the thermostat in a pan of water and it opened around 180 also drilled 2 .. 1/8th inch holes in the side of it and it did seem to help. I ran it around the block about 7 times it hit 185 and held for awhile and then started climbing to 200 . 210 and 220, 230ish ..I ran it about 20 minutes and then came back home when it hit 220-230..Pulled it in and checked both top and bottom hose both were hot No overflow, no steam. I'm hoping its a faulty reading on the temp gauge but I am getting the original gauge fixed and goin to reinstall it with a new sensor. Thanks for yalls help and if you fellas have any more suggestion I'm open for them... never to old to learn something new.

 

Bow_Tied I did pull it in the shop and jacked up the fron end and added more water about a gallon. Then topped it off when the water fell again and waited till it started creeping out of the neck of the radiator... I haven't had it cranked in about 2 days.. I had a 76 back in the day with a 350 in it. and it was a awesome car..