excessive coolant pressure problem!

[the t3d]

i've run into a dilemma...my car was perfect before all this. i just got my aluminum radiator, so i decided to install it this weekend. i figured i would replace my thermostat while i'm at it. i ran some flush through it and then i flushed a hose through the motor to clean all the nastiness. i didn't have any coolant issues or overheating or nothing. i put all together and filled it up and let it run with the cap off to let the air out and coolant just started spilling out of the radiator like a geyser. so i just shut off and top it off again. i put the cap back on and let it run and pressure built up some much that it started leaking out the cap and started to overheat. so i shut it off again, let it cool down. checked the level, topped it off and let it run again. no overheating at all. it's almost like the new thermostat didn't open the first time. but now after i drive it out alittle, it's fine, but when i stop and turn it off, coolant pressure builds up spill out again. none of this happened...ever until i did this. my motor is fully built and fine with a MHG and all that jazz. i have just about 1400 miles on the motor. this is pissing me off. i'm thinking maybe i really didn't let the air out of the system and it's just that. my heater control valve doesn't seem to be working, so i'm probably just going to bypass it to eliminate that. i'm just looking for possible ideas. i'm going to a block test JUST to make sure, but i doubt that's the problem. i'm also gonna pressure test it and what not, but like i said, i'm looking for possible ideas of could be causing this just after what i have replaced

sorry for the long story...i just wanted to give as much info as possible

thanks, t3d

 

[grimreaper]

so the cap is leaking? wheres it spilling out of?

 

[the t3d]

it seems like it's spilling out of the cap and the overflow bottle

 

[max-89supra(t)]

possibly a bad thermostat??

i bought a new one from napa and it went bad on be in a week, it was pissing me off cuz i thought it was good, i learned my lesson the hard way and only get thermostats now from toyota, by the way the toyota ones are almost twice as big which surprised me at first

 

[grimreaper]

You should be able to tell if the seal on the cap isnt holding. is the top of the radiator wet with coolant ?

 

[bfr1992t]

I've had similar problems. My car will boil the coolant without the rad cap on - no pressure increase to raise the boiling point. Second problem is you likely did not get all of the air out especially w/out the heater core circulating. You can open the valve by hand and use a zip tie to secure it if the dashpot has failed. Also as others noted use only Toyota t-stats.

I'd recommend you top it up while it's cold, put the rad cap on and squeeze the top hose, then top it up again and work as much air out through the top hose as you can. Fill the overflow 2/3 of the way. Make sure the overflow hose from the rad all the way to the float in the overflow is in good shape. Go drive it easy, you will most likely see the temp gauge spike once or twice when the t-stat opens (air bubbles passing through). Shut it off, check the overflow (without uncovering the float from the coolant, you don't want to introduce air back in to the system), it will likely be full. Let it sit for a few minutes, fill it back to 2/3 if needed (remember don't remove the hose/float from the coolant), restart and drive again. Repeat as necessary. Be sure to check the overflow before you start it the next day and for 2-3 days after. You should be able to let it settle in between the hot and cold lines.

This is the method I use on several Supras and it works every time. I've tried just about every other method and always end up having to perform the steps above to get the last bit of air out.

I cannot stress this enough, do not pull the overflow hose out of the coolant as this will allow air back in to the line. You're just chasing your tail when this happens.

 

[the t3d]

well, i haven't had the chance to get any work done on it yet. work is pretty busy and i'm eating lunch now. the first time pressure built up, it forced itself out the top of the radiator cap.

yea i don't the HCV is opening up at all if anything. i'll see if i can do what was mentioned to keep it opened up manually. i'm hoping it's just a bunch of air. i just don't to ruin my nice, new motor. yea the thermostat i put in it was a Stant...

 

[supra*13]

Did you put the thermostat in the wrong way. the previous owner of my mk3 sold it to be because he said it had a bhg. but the thermostat was in backwords and bad radiator.check if is in the right way.