My Trans Am boils the coolant in the reservoir after a long drive. The car doesn't run hot at all, around 180 while driving and 220 when at a stop for a while. If I press down on the radiator cap, the boiling stops. Any ideas what might be causing this? There isn't any white smoke out of the pipes either, even with a gutted cat.

 

Tried changing your cap?

 

 

I did. I'm thinking maybe the top of the radiator where the cap screws on is effed up. I changed the cap already, and put a slight bead of silicone on it to help it seal better. It seemed to work for a bit, but now it's acting up again.

I just hope it isn't a headgasket, because if it is, I'm gonna blow a headgasket.

 

To check for an internal intake/head gasket leak, you are looking for combustion gasses which can build up pressure in your cooling system. With the engine cold, take cap off and start the engine....let it run for a little bit and it doesn't have to get up to operating temperature either-if you see constant little bubbles or (sporatic large ones)appearing in the radiator, then yes I would say you have an internal leak-usually its a head gasket issue but I wouldn't rule out an intake gasket failure.

 

screw the cap on all the way? you'll have to push down and turn.

sealant isn't a solution

 

It is.

 

Ok I'll try that thanks.

 

Sealant isn't a solution. You already said so yourself.

If the cap is new but still won't stay on, the neck of the radiator is prolly wore out or cracked. Sounds like radiator time.

Not a head gasket for sure; not an intake gasket for even surer.

 

That's just what I needed to hear. A head gasket is no easy task. I really don't want to have to do that, and I won't let a shop touch it.

 

You said =( I changed the cap already, and put a slight bead of silicone on it to help it seal better. It seemed to work for a bit, but now it's acting up again. )

If that worked in even in the slightest way it could be the seal between the cap and neck.

Use a fine toothed flat file to level the top of the fill neck just "A LITTLE" .

(There could be more than 1 problem)

 

Rent a pressure tester from any decent parts store, put in on your radiator and see if you can pressurize the cooling system manually to determine whether or not you have a leak. I know from experience that a failed head gasket will induce more pressure into the cooling system...that and I've diagnosed quite a few internal leaks this way over time.

 

Forgot to mention this happens when the car is shut off, don't know if that matters.

 

Is there water or coolant in the radiator?

 

I think it's mostly coolant at this point, but at one time i was in a pinch and had to put water in it.

 

Someone mentioned this earlier but you should rent a pressure tester and see if there is a leak somewhere in the system. A leak would cause a loss of pressure build up and cause a lower boiling point for the coolant. Go to your local advance auto parts they always have one to rent.

 

I'm going to do that tomorrow. I have one at my shop.

I got an action shot of the coolant in the radiator.


Doesn't seem to be any bubbling.

 

50/50 or straight coolant? That stuff looks pretty green. Run more than 50% coolant and it actually hinders cooling efficiency.

 

I think he already knows there's a leak and where it's at.

 

Car held 12 lbs of pressure in the system with a Snap-On pressure tester. Had the gauge on it for the better part of a minute and it showed no signs of bleeding down.

I'm thinking the neck of the radiator is just a little worn. Seeing as there are no signs at all of a head gasket leak, no white smoke, held pressure, no milky oil, and doesn't run hot.

 

Did you check the thermostat?

 

I had a similar problem, and here's what I did to make it go away

Fix broken air dam
Add thermostat (none in the car when I bought it as it turns out)
Flush system
New radiator
Fresh coolant
New hoses

So far so good

 

Thought I'd update this. The radiator cracked a couple days ago and spewed coolant all over the place. I put a new one in (easiest rad I've ever done), and the boiling has gone away, probably from the new neck. Looks like I do need a head gasket though, you can see the constant stream of bubbles, that's with the thermostat open. Guess I'll just take it one step at a time, and hope I can keep my sanity. Gonna have the heads gone through while I'm at it, checked for straightness, valve job etc.