Does this appear to indicate a blown head gasket? My 02 Coupe is overheating to 255*+ although no white smoke from the exhaust or loss of power(though I haven't driven it hard since it first overheated). The oil on the dipstick appears ok but I checked under the fill cap and found this.

 

How's the coolant look?

 

What happened regarding the overheat? Any work on the car? When/ where does it overheat, what are the circumstances? Do the fans come on? Not low on coolant?

 

The fill cap can get CONDENSATE contamination easily..

Overheating:

When does it over heat??
Traffic?
Sitting Still idling??
Highway speeds???

Provide the info. Here are some things that I would check:

AIR FLOW: Look at the air inlet under the nose for blockage/trash!!

Remove the plastic shroud under the air bridge (between the radiator/AC Condensor and make SURE that there isnt any CRAP between the two.

1. Are the FANS coming on when they are suppose to?

2. Have you BURPED the coolant system?

3. Do you have PRESSURE in the system when its at NORMAL Operating Temps??????



Change the T stat if in doubt!

BC

 

for what its worth, I had an almost exact same build up on my c5 corvette which had been sitting for a year or so. I was real scared I had a blown head gasket.

I had a mechanic do a block test and compression test and it turned out to be nothing more than condensation build up.

So I wouldn't jump to any conclusions based on that white residue on the cap until you have done some proper diagnosis on the overheating problem.

 

Hasn't the temperatures gone south in Illinois over the past couple of weeks? That might be the source of the condensation. As recommended, check the typical sources of overheating especially the condenser and radiator for junk. I only got to drive mine 1,000 miles this year but one of my winterization rituals is to vacuum the condenser, and there was plenty of stuff up there in only that short amount of miles including leaves.

 

Thanks for the replies, guys.

The car will overheat at idle or during in town driving. During highway driving it will hold about 200-205*, granted this is in cooler weather now this time of year. I have replaced the thermostat, coolant temp sensor and water pump. I removed the radiator and ensured it and the AC condenser were both clear of obstructions. I laid the radiator flat on its back and filled it with water and it came up equal on both sides so it seems like the radiator is not plugged up. I have made sure I purged the air from the coolant system every time anything is removed. The fans appear to be working properly coming on low at 226* and high at 236* according to the DIC. However they seem to have basically no effect. This is especially evident while the car idles as you can obviously hear the fans kick up to high at 236* and the temp just continues to climb. The car is essentially stock with only a dual cone intake from a previous owner and a GHL catback installed about a week prior to the overheating beginning. I am beginning to run out of ideas. A friend of mine suggested my cats may be clogged but I hadn't heard of that causing overheating on these cars and I imagine it would throw a code.

 

I think the radiator can have a lining of deposits in the tubes which will impede heat transfer yet still pass the test you performed.

Did you test the new thermostat in boiling water to make sure it opens fully? I never used to do that but do now. Ask me why.

You did not say whether the system pressures up-

If the coolant air bleed ports, tube or hose is blocked or partially blocked there could still be air in the heads. Being an '02, it only has the front ports connected, so it is important to confirm that the air is OUT. In my view, the only way to make sure the air bleed pipe and ports are open and the air is out is to vent the air bleed hose into a container on the garage floor with the engine running and system at pressure.

To do this, you need to cut the air bleed hose and put in a 1/4" barb- barb hose connector so that you can bleed the system into a container on the floor and plug the hose end going into the radiator (temporarily). Below is a picture showing the barb- barb connector on my car:




Below is a picture of the cobbled up rig I use to bleed. The clear vinyl portions of the hose are so you can see the bubbles coming out:




The short piece with bent over end is to temporarily plug the hose going into the radiator while you bled the heads. I know it is all kind of half- assed, but it works:




The last time I bled the heads on my car, it took nearly a QUART of coolant coming out before the bubbles stopped. When you are done, reconnect the air bleed hose at the 1/4" barb- barb connector and pour the coolant in the container back into the surge tank.

Don't let the surge tank get too low before stopping and refilling!

 

Do a block test, relatively easy and cheap to do and will remove all doubts of HG issues.

 

You can borrow/rent a block tester from AutoZone -- though be sure it comes with or buy good test fluid.