So whenever i take off the rad cap to check my coolant, it will kinda release pressure, not alot, but a little bit.
After checking the coolant ill go to start it and itll have the exact symptoms of flooding. It almost starts but wont.
I have checked to see if the coolant seals are blown, i do not think they are as when i crank it with the egi and ignition pulled,
nothing comes out with an open rad cap, if that makes sense.
Also the coolant does not seem to smell of combustion gasses or have any oily film.
This problem has been annoying me for a while, i first thought it was a blown coolant seal, but iv'e began to doubt it. The car is an 86 gx n/a.
Thanks

 

Forgot to mention that this is on a cold engine, one that hasnt been started for a day.

 

Confirm your add coolant sensor works, if it does then no need to remove cap. Next check compression.

 

I check the coolant regularly because i have a problem with the overflow not going back into the system and the buzzer goes off. Does a conventional compression tester work or does it need to be modified, i remember reading somewhere that you had to remove a check valve or something.
thanks

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/public-service-anouncement-pinhole-radiator-leaks-825792/

Check out my thread.

Also, you may have stop leak in there and either forgot about it or a previous owner added it. Anyway, from my experience, even with other vehicles, remocing the radiator cap or squeezing hoses can actually unplug any holes stop leak has sealed. It's amazing it can hold up to 1 bar of pressure inside the very hot cooling system, yet not be able to take any sudden pressure spiked.

By the way, that wasn't pressure being released, but vacuum in the system being relieved.

 

Im sure it was pressure as the cap literally popped up, the thing is it wasnt a singular occurrence, every time i remove the rad cap this happens. The cars away for the winter so im just going through it and getting rid of some of these problems. Maybe its time to get the turbo swap on the roll...

 

It popped off? Strange, the cap is supposed to reliece pressure at 0.9 bar. If you have enough pressure to pop a cap off, and it be just AIR, then I'd be suspicious of the cap.

Any more details exactly on the cap popping off? Did a bunch of water come with it? It was the morning with the engine cold right? The system should have a vacuum then.

 

That's the weird thing, it wasn't high pressure, it didn't go flying or anything, but there was pressure in there for sure. i don't see where the pressure would be released from this cap as there is no hose feeding to the overflow tank on the filler neck. The hose comes off a separate rad cap in front of the rad with a small hose leading to it. It doesn't match anything i've seen in the FSM...

 

So today i pulled all the rad hoses to check for leaks and the fluid in the resevoir has brown chunks in it, not a good sign. On piston engines this usually means blown headgasket iirc, Would this be a symptom of blown coolant seals? The other thing is i dont know when the coolant was last changed, but ive never seen something like this happen from old coolant.

 

not maintaining coolant causes rust, rust damages the coolant seals.

 

I just vacuum tested the cooling system and it did not hold vacuum, there is a pinhole in my rad somewhere. this would explain why my overflow tank isnt draining back into the system. It seems to hold vacuum cept for that hole.