Boiling the coolant out of overflow. Everything else is fine.
 

My NA8 is losing coolant by boiling it out of the overflow after the car warms up and then I stop and turn off the engine it starts gurgling and losing coolant out of the coolant overflow tank the coolant all goes into the overflow and when that fills spews out coolant.

The car doesnt overheat at least if the gauge is to be believed and drives fine.

I have bled the system and replaced and flushed cooling system multiple times.

New radiator. New thermostat. New rad cap.

Old rad cap tested fine under pressure as well as the new one I got just to be sure.

Entire cooling system passed pressure test.

I have tested for combustion gasses in the coolant and all tests negative.

No other leaks can be found after adding dye to the coolant.

My only other solution is to replace the head gasket. I haven't thought it was the head gasket because the combustion gas tests in the coolant were all negative there isnt any leaking around the head or steam out of the tail pipe or any other symptoms I can find no oil in coolant or coolant in oil.

My question to you is there anything I am overlooking before replacing the head gasket?

TLDR Coolant loss from boiling overflowing the overflow tank no other signs head gasket is bad or other leaks. Is there anything else I have missed?

I had this and it was the head gasket. There was a small carbon trace from the cylinder to a water jacket passage. In street driving I didn't have any issues. On track, I would start bubbling coolant out after about 10 minutes. There weren't any other head gasket signs.

I didn't do a combustion gas test, so I don't know if that would definitely show this failure. All that's needed is enough pressure to overcome the radiator cap, so I'm not sure that there is enough combustion gas getting into the coolant to be detectable.

thanks for your reply this gives me confidence I will be able to solve the problem.I thought it was really wierd the gasket would fail but show no symptoms except the boiling over when stopped. Doing the job isnt hard but I didnt want to have the car unable to drive if It was something else.

I did a gas test about 4 or 5 times. trying to get a positive but I couldn't either the test fluid was contaminated by coolant or I would just get a negative. It was wierd because there was lots of bubbles coming out of the radiator neck but maybe there just wasn't enough exhaust gasses.

Its possible that only when the motor gets hot that it really started leaking and then when it stops the heat causes the coolant to boil out of the overflow.

What happens is that you overpressurize the coolant system with the leaked cylinder pressure. This causes coolant loss through the radiator cap and also introduces air pockets in the cooling system. The air pockets result in localized boiling/overheating.

I struggled with this for a while. At first it was just mysterious coolant loss with normal temperature indications. It finally got bad enough that I could see flickering overheating indications on the temp gauge and when I got off track the coolant would continue to spill from the overflow for several minutes. That's when I swapped the gasket and found the carbon trace.

Should it be obvious once I pull the gasket? I will get started on this tomorrow. WIsh me luck!

I had that happen after our car overheated and warped the cylinder head, so hopefully its just a gasket.

I wish I had taken a picture. Basically, there was a dark line from the cylinder to one of the water jacket passages (on #2 in my case). It was evident on the engine block and on the steel cylinder pressure ring embedded in the composite HG (this was on a 1.6). It wasn't huge, but definitely there.

With a MSL gasket, it can be harder to see and cracks in the head can also be a possibility.

Well got the head off it wasn't too terrible but lifting it off the block was pretty awkward.

I can't see anything wrong with the head gasket. It isnt like a composite gasket thats for sure. I cant really see any things wrong or what cylinder might have had coolant in it. Its possible it just wasnt enough to notice anything funny with the spark plug or the valves and top of the combustion chamber of the head.

One of the head bolts did come up with a bit of coolant not sure if it from the head being loose or leaking coolant to a head bolt.

I checked the head with a square I know its not as accurate as a machinist straight edge but I didn't look bad at all a .005 feeler gauge fit in between obiously I will be getting it checked by a machine shop.

The only odd thing I found was on one of the cylinders in the middle two of the head bolts we looser than the others. Not super loose but enough to tell the difference between the others.

SO far my theory is this was the problem.

Hopefully the head checks out fine with the machine shop or just needs a shallow cut and the head gasket failed but I couldnt see the failure.

I just want to fix this thing and be done with this problem.

What is odd about the whole thing is the head was completly rebuilt and has less than 30k miles on it.

When I had the problem, there was no leaking of coolant into the cylinder, only leaking of gases out (under high pressure/track conditions). With street driving, there was no leakage whatsoever.

Take pictures of the head and block surfaces. Maybe we can spot something.

Heres some photos guys. Hopefully you can spot something I can't because it looks fine to me.

Absolutely no idea if it is significant but the gasket impression in the head seems to be washed away a little between 2 and 3 on the exhaust side (the very middle hole), but not into to hole however.

But I might be trying to make something fit with your notion that the bolts there were looser.

I'd have to agree. Gasket wasn't sealing on the exhaust side between 2 and 3. Both head and block look abnormal there.

I think I see it now. Are you guys talking about the brown rusty looking areas?

The blue cat or the red cat?

Attachment 234858
This fuckin' guy :laugh: :laugh: :laugh:

I'm of very little use here posting from my phone, but I'm looking at the blue

So what do I do differently now we have a likely cause besides continue with getting the head checked and/or machined and put a new gasket in?

220grit emory cloth and heavy flat sanding block. Use a good straight edge and feeler gauge to check for warpage side to side front to back and across both ways. If all is good use a fine wire wheel to clean all the steel bits, and throw it back together. If its warped it needs to go to the machine shop.

What constitutes a good straight edge? I don't have access to dope machinist rulers.

I think I might go the chemical gasket remover and plastic scraper route instead of removing material.

Get an extension, the longer the better. I find 1/2" seems to be better than 3/8" but that may just be me. Find a glass table or a mirror and a set of feeler gauges. Put the straight edge (socket extension) on the glass and roll it. If it clicks, its not straight. If it does not, rotate it around the glass and use the feeler gauges to check for low/high spots. Once it sits flat (where you can't fit your smallest feeler between the glass and extension) use a sharpie or a paint pen to mark the "top" of the straight edge (extension). In theory, the underside will be flat. Obviously the square end needs to hang off the glass.

Good luck and godspeed.

Edit: obviously this should not be used with the sandpaper...

What is the extension for?