The engine is in a vette, but I've recieved great info through this site, so I'll just ask here. About once out of every 15 starts or so, I have this problem. The coolant temperature normally comes up to between 205-220, then rapidly goes down to 180-189 and stays there no matter what, however, it rarely goes up all the way to 260! before rapidly coming down to normal. This is really scaring me, it only happens for about a minute or 2, but it can't be right.

I checked the coolant resovior and it was low, so I added some and will monitor that, the radiator is full though. Engine doesnt show any signs of being overheated, oil temperature never comes over 185.

I have aluminum fast burn heads, so this is really bugging me, they don't take heat like iron heads.

Any ideas? I hope I don't have a head gasket issue begining to form, but I'm prepared to do whatever it takes to save the car.

 

One more thing, the three times it has done this, it was after a letting the car sit for a while (overnight). Maybe the thermostat is sticking? Well, hopefully its just a goofy gauge, but I can't be that lucky.

 

No ideas guys???

 

hmm, kinda a overheating problem people gets.

First is this engine in a camaro?
(kinda assuming)

your thermostat could be going out, maybe replace that.
Im thinking maybe what you can do is put in a lower heating thermostat, and put on an Air Dam.

The air dam seems to be alot of people's problem..

When I got my car, it over heated like yours is doing, was getting kinda tacky, me and my dad had to replace two thermostats, new hoses, new water pump, and ready to put in a new raditator, but a friend told me I was missing an air dam, and that Sovled the problem.

if you dont know what it is (you may know, or not, I can be wrong)

The air dam is pretty much a plastic board that is bolted on underneath the raditator, and when you go down the highway or road, the air dam forces the air up to your raditator to breath, the camaro grills werent really that great having air going into the engine.
this board can be found at Hawk's third gen auto parts for $80 (where I bought mine.... that is pretty pricy)
Its cheaper to go to Classic Industeries.. they have one for $30 if I remeber.

if you want a pic, you can search it up on this board, of other threads, they got a couple pictures and you'll get an idea what it is..

well.. if that's not it, then it can be a bad sensor just going nuts like you hoped, that can also be the problem.

Hoped this helped.
Tim

 

Engine is in my 85 vette, so I don't know about the air dam thing. I saw it that the coolant overflow tank was low, so I added coolant and havent had the problem in a few days, hopefully I was just low on coolant.

 

That could be it too.

hopefully you dont have the same problem I have with my engine.
I would fill the coolant up, and about a few days later, it be almost all gone.
I check the raditor and everything, and I cant find the leak, but I do find a good puddle on the pavement in the morning, and I checked the whole car, and cant find the leak...

but I dont think corvette's had air dams... so I guess my advises are pretty useless :-[

 

Something all of us with MiniRams have to deal with....

https://www.thirdgen.org/forums/alte...ck-issues.html

 

Well, last night I guess the thermostat went out. I noticed the temp come up to 260 again, but it didn't go down, so I pulled off and found coolant had blown out of the overflow tank. Mechanic came and picked it up, put a new tstat in, and everything is fine now. Now I'll be interested to see if it ever gets up that hot again, hopefully it was just sticking before.

 

Either the thermostat wasn't the problem, or this one is bottoming out worse than the other was. I drove home from the shop just fine, but today its temperature has went up everytime I ran it and never came down.

Could drilling some holes in the thermostat fix the problem?

 

Just to throw my 2 cents in, you've said you ran low on coolant. Have you bled the air from the system? Air trapped in the system can cause temp spikes like you described. Although if is getting hot and staying hot now, there may be another issue. Have you checked/replaced your rad cap? Is your gauge accurate? Are you relieving pressure into the overflow after the engine shuts off? Do you hear it boiling? How is your coolant mix?

 

The radiator cap is brand new, and the gauge is accurate, when the temperature comes up the water level rises in the overflow and will overflow if hot for too long. No boiling sounds though, so hopefully no headgasket or cracked head. No coolant in oil or steam out of exhaust, car runs too well for this to be a major issue.

I don't know the coolant mix exactly, my best guess is 40% antifreeze, 60%water.

All the hoses are in good shape, no leaks anywhere. I think the thermostat is just bottoming out and isn't allowing enough coolant to flow. I'll try drilling the holes and if that don't work then I'll

 

Update:

Tried to "burp" the system today, but didn't get any air bubbles, just wasted a bunch of coolant. I'm assuming that there is an air bubble of large size under the thermostat and will not allow it to open at all. The thermostat is not bottoming out in the miniram intake either, its a newer style.

I'm going to drill some holes in the tstat tommorow and see if that corrects the problem.

 

hmm... I guess that could work, or if you feel for spending about maybe a little more for a new thermostat (I can tell your probly spending alot of money on figuring this, I know money is an issue x.x) you could get a "High-Flow Thermostat" from jegs, I put that in my car, didnt really help the heating problem, until I put the air dam on, my point what that does is, I think the high flow will let it flow more so it doesnt let the car warm up, because my temp gauge never moved an inch, even on the hottest days, still be down below the 100. untill it hit winter.

well... other then that, I dont know what to say man.

 

Drilled the holes in the thermostat today, and the problem is solved. Car never got over 183 degrees and held between there and about 175. I guess I just had a nasty air bubble.