Probably have a bad radiator cap, but want some confirmation. While the car is running, no issues. Runs till it reaches ~220 and the fan turns on. Cools down a bit and the fan turns off. Heater works and water flows. Car hasn't had a cooling problem since I bought it a few years ago and has always been in warm climate (California and Hawaii). HOWEVER, when I turn off the motor, the overflow tank starts bubbling. Start the car and it stops bubbling almost immediately. I did this three times to make sure my hearing wasn't as impaired as my vision.

New cap will be installed tomorrow, I just need someone to explain why this is happening. I've been a shadetree mechanic for about 20 years, but have not encountered this problem? yet.

By the way, I checked the compression as a precaution and they were all between 170psi and 183psi with the average at 176.5psi. No blown head gaskets! Good news story: the miss I had prior to checking the compression is now gone. Must have been a loose wire!

 

When you shut off the car, the water pump stops turning and coolant stops circulating. The coolant inside the block and heads is still absorbing the heat of the engine, but it isn't being circulated through the rad to cool it down. It gets hot enough to boil, and the resulting pressure forces coolant to vent out the cap. When you start the car again, the water pump starts turning, the coolant starts flowing through the rad again, and the boiling stops.

 

Sounds like a logical explanation. I guess I can consider this normal? This is my third 3rd Gen and I do not recall any of them doing this. Thanks.

Mike

 

It's somewhat normal, if the rest of the cooling system is working properly, but you could be overheating, or your radiator cap could be weak.

 

It has never overheated. To be sure it wasn't, I let it idle until the fans kicked in and the temp immediately started to drop.

Mike

 

a bad radiator cap can definately lead to this. a radiator is a pressurized sys tem, like a pressure-cooker. thi higher the pressure the cap can maintain (safely), the higher the boiling point of the fluid is...something a chemistry student is very familiar with. If your cap isn't holding the right pressure, the fluid boils more easily, causing the bubbling noise you're hearing.

 

Radiator Cap. Replaced it yesterday and all is good.

Footnote, it had a 15 psi that I put on a few years ago in accordance with the books at the auto parts store, but the place I went this time suggested a 16 psi. Probably not a big deal, but different none the less.

Mike

 

one pound difference won't make a very big difference. Ideally you should go for what the manufacturer had originally. more is better, but the rest of your system has to be able to handle the pressure (hoses, etc). Radiator cap pressure testers exist, I'm sure that your local shop, or even parts store would be able to test it to see how much it's holding.

 

Yeah, my camaro has dat problem also... I just replaced the radiator cap... But I noticed crap in my coolant... And i replaced the coolant when i installed the water pump... I should have flushed it after i put the new water pump...

 

And as evidence, theres sludge residue in my reservoir tank...

 

sorry to somewhat hijack the thread, but....
Having contaminants in your coolant can be a sign that you've got much bigger problems. A cracked head or blown head gasket can allow oil or combustion residue into the coolant, among other problems. To help diagnose those problems you should have a compression test done on your motor to see if any cylinders have low compression.
If the sludge is oily or floating in the coolant, this is definately a very bad problem you're dealing with.
Additionally, coolant should be completely flushed out every couple years, regardless of if it's clean. All the additives break down that help stop corrosion (very bad, and a high likelyhood for causing your sludge) and lubricate the water pump (you mentioned a pump replacement), among other things.

hope this helps...
~Erik~

 

I dont know exactly where to go where i can get a radiator flush because i dont just want them to replace the coolant but i want the damn thing to be cleaned as well... Thanks for the suggestion

 

You can flush it yourself easily enough.

 

if you're really interested in getting everything totally cleaned out, here's my suggestion: empty our your cooling system (take the old coolant to somewhere that can recycle it), and refill it with clean water. Run it until the thermostat opens (to flush out the engine too), then let it run for a few minutes, and drain this water. do this a few times, or till the water is much cleaner than the first flush. If you're really going for super-clean, take your radiator to a radiator shop and have them boil it out. after a few flushes, refill your cooling system with fresh, properly mixed coolant, making sure you top it off again after the thermostat opens, as all the air bubbles in your motor will work their way out.
~Erik~

 

I plan to give my radiator a super flush. Using that prestone super flush. I did it to my other camaro and the damn thing worked, after several putting in the water, then let it flush till the rust went away.

 

Actually, I used the super cleaner from prestone. I bought it at Autozone today... Oh my *** did dat radiator had shyt on it. IM suppose to drive it for 3 to 6 hrs... Ill drain it tomorrow and make sure it cleaned my entire water thingy system or something. But I didnt realize what catastrophe my engine was going through.