Ok I have an issue that is confusing me. My Camaro (1984 auto vortec head 355 street demon carb) constantly has bubbles blowing into the coolant reservoir whenever it runs. It’s been doing this for a while and didn’t seem to have any other problems. Replaced the radiator cap and no change. Oil is fine (no coolant in it), no leaks, and didn’t overheat until recently. After it cooled down I checked the coolant level and it was of course way down. Filled it back up and did my best to bleed the air out. Replaced the cap again just to be sure (how good is QC on a $5 part lol). Still no change. I didn’t think I was losing any coolant until this past time when it overheated. Now I know it has to be going somewhere, albeit very slowly. My paranoid mind is going straight to head crack or gasket, but there aren’t other symptoms (oil is fine and not regularly overheating). Is there something easy and simple I am missing?

 

It does sound like either a head gasket or cracked head. The breach is likely between the cooling system and the combustion chamber. If the leak is small enough, it will just burn off the coolant and won’t show up on the oil or vice versa. Pull the plugs and see if there is one that looks different than the others. Compression test might tell you something as well.

 

when I bleed coolant system, I just bring the car to temp with rad cap off and watch for it to cycle thru the coolant a few times. not saying that is your problem tho. sounds like to me you may want to run a coolant pressure test and see what comes of it. you be surprised what you might find.

 

Thanks for the info, I hadn’t thought about a leak being there that wouldn’t allow it into the oil. I believe I’ve read that Vortecs are prone to cracking, just not sure where the weak points are. Guess I’ll do a bit of research then pull some plugs. Maybe it will at least point me in the right direction before I jump to a compression test. What might a plug in that situation look like?

 

Thank you, what I did was similar. Had the cap off and ran it until the coolant started pouring out a bit. I’ll try locating a coolant pressure tester and see what happens. Appreciate the reply!

 

It may not show anything, but if there's enough coolant going into that cylinder, the plug may look cleaner than the others.

 

Compression test to see if there is a weak cylinder. Do the compression test with all the plugs out and examine all the plugs while they are out.
With all the plugs out, crank the engine over to see if any coolant sprays out a plug hole.

Cooling system pressure test with the plugs out and you may hear or see coolant going into a cylinder however 15 psi coolant pressure test may not be enough pressure depending where the compression is coming from. At least a compression test should have much higher pressures.

 

OK I’m hoping this is resolved. I took it out today and drove for quite a while to make sure that it was fully warmed up and stayed that way to see if it was going to overheat or show any other problems. Temp stayed rock solid regardless of whether I was driving or stopped at a light for any length of time. Ran and idled really nicely except for a slight knock but only when it dropped into OD at low speed (I will be playing with the timing to get rid of that). When I got home I popped the hood and didn’t see any bubbles in the overflow. The only thing I saw was that it looked like a little bit of coolant spit out around the radiator cap and it was a touch loose. I thought I had tightened it properly but maybe not 100%. I’ll be doing this again tomorrow after checking the radiator coolant level when it cools down this evening.

 

That’s a bit promising. Drive it a few more times and don’t open the radiator cap. Let the coolant expand and contract in and out of the reservoir and work out any remaining air (it may take some more coolant from the reservioir as it works the air out). If after a few more heat/cool cycles, the reservoir cold level stabilizes and it doesn’t overheat, then you may just be ok. Then, just keep an eye on the reservoir long term and watch for loosing coolant.

 

Its possible you didn't build enough pressure to invoke the problem, since it sounds like pressure was escaping via the radiator cap. I had a small coolant leak that I could not find until I pressure tested. it was tiny, a 1/2 turn of the clamp was all it took to seal it. have had same experience with other cars as well, tiny, hard to find leaks, that leave no trace.

 

OK more good advice, thank you. I’ll not touch it and drive, check, drive, check and see what happens. Guess it was a good idea to replace the replacement radiator cap LOL. 🤞

 

I drove it more and longer today than I had in the recent past. I do know that this cap fits more securely than the previous one, which is part of why I wanted to replace it.
Those tiny leaks can drive you crazy can’t they??

 

This is a little pricey but if your problems persist this will tell you for sure if you are leaking exhaust gas into the coolant

Lisle Combustion Leak Detector 75500 | O'Reilly Auto Parts (oreillyauto.com)

 

OK spoke too soon. I believe you were right LiquidBlue that the cap not being secure allowed any air to be pushed out the cap instead of into the overflow. After driving it more (with the cap secured) it was bubbling like crazy and the level was low when I did finally open it. Refilled it and still bubbling. Took Vinny’s advice and got a combustion gas tester from Amazon ($22, why not?) that will be here tomorrow. Wish me luck, I’ll report back when I get a chance to test it. Thank you all!!

 

Not great news, I got the tester and set it up in the radiator. After running the engine for a few minutes the indicator fluid looked like it was starting to turn from blue to green when I shut off the engine. Coolant spit out of the radiator and through the tester so I couldn’t verify it changed color. Tried it again with the tester in the reservoir but there was not enough pressure to push the gases through the fluid until I shut off the engine when it bubbled through for a couple minutes. When it was done the fluid was for sure more greenish than the deeper blue color it was. I’ll test it again later tonight but it’s looking more like a bad head gasket or cracked head 🤬

 

Retested it and it definitely seems there is a problem. Took a before pic:

And now the after pic


So is there anything else that can allow exhaust gasses into the cooling system other than a bad head gasket or cracked head?