Blown Head Gasket?

[ms!3]

Got my car back together a couple of weeks ago. Pulled motor, replace all gaskets, clutch, and mounts.

heres the thing. when i first got it running it was fine for about two days. Then it started overheating on me. So i took out my thermo and it ran fine. Stopped overheating. Now my problem is Pressure buildup. Since i removed the thermo it doesnt overheat but builds up pressure. I have to let it out after every drive through the rad cap. Got lazy one day and didnt let the pressure out and the pressure split my top rad hose. system has been bled properly too.

Now its doesnt smoke, water doesnt mix with oil, no loss of power, comp reads 180,180,175,170. But its constantly builds up pressure and there are constant bubbles floating to the top of the rad when you let it run like a blown head gasket would do.

my water pump is fine, my rap cap is fine, not using a thermo at the moment so that doesnt even matter. I flushed my block, and rad when they were out of the car so there is no blockage that i know of.

The only way i can think of all this pressure build up is a blown head gasket. But i dont have any other symptoms. This is a tricky one, Im stumped. any help?


edit: also keep in mind im not using the right pressure relief valve bolt because i lost it. Im not sure that is the reason tho.

[DDSR240]

did you make sure that you bled ALL the air out of the cooling system bc thats what it sounds like to me hope it helps.

[ms!3]

ive been bleeding it for about 2 weeks now. let the pressure out through th cap all the time. let it idle with cap off alot. Even did it the right way one time where you jack up the front of the car, remove rap cap and let it idle.

Mabey im justing doing it wrong. i dunno.

[georgesal]

there is a tester that can test to see if you are getting pressure from anyone of your cylinders in you coolant. the tester changes colors in the presence of exhaust gasses.

[ms!3]

yea ive heard of that. mabey autozone will do it. did alittle more research on bleeding the system so hopefully that will fix it all. thanks

[69datsun510]

You need to put the thermostat back in. You can test the thermostat in pan of water. Then bled the system make sure you put the heater on hottest setting and high, squeeze the hoses. The radiator is designed to have pressure between 8-14 lbs, stated on the cap, and the cap should vent above that pressure, if it's not, it's bad. The pressure raises the boiling point of the coolant, so some pressure is always present with a hot motor. Hence, the warning not to open when hot! Your radiator can not work correctly if the coolant doesn't stay in it long enough, by removing the thermostat, the coolant circulates to fast and not aloud time to get cooled, and compounds your heating problem. You need the thermostat in to fix your problem, if the head gasket hasn't blown yet.
If you bleed the system correctly, the coolant should be all the way at the top of the neck during the whole procedure, loosen the small 10mm coolant bleed screw and the reservoir tank filled to the correct level. You didn't say if you have a reservoir or not, they tend to crack and leak. If so, get a replacement tank, you need to run one with this system. You have to make sure all of your hose connections are tight, including the heater hoses. Check your timing, to far advanced can cause the motor to overheat. Good luck