Ok. I have recently swapped a 96 block/head into my s13. did full manifold swaps, etc.. for about 3 days, it ran just fine, no problems at all. now when i got back from a little road trip the other day, the car started running a bit hot. I got back to my garage to find out that there is coolant spitting out of the overflow. Thinking that it might just be air, i take the cap off, top off the coolant, and let it run with the cap off expecting to see some air come out of there. after the car got back up to operating temp, it was like the coolant was just boiling out of the radiator. so i grab my lower radiator hose, perfectly cool temp. so then i think that maybe my thermostat isnt opening. so i took the thermo out, put it in some boiling water, and it opened right up. after that, i put the thermo back in(with the jiggle valve facing up), and proceed to bleed the system again. same result; boiling coolant and cold lower radiator hose. so i watch in the radiator, and it seems like the coolant is not circulating. maybe water pump? so I swap water pump with another know working pump I have sitting there. once again, same result.

after all this, with a cringe, i think maybe the headgasket is leaking, however the car is running fine and not smoking at all. so i throw a compression tester on there, and get 155-160 across the board(i know, a little low, but according to FSM min: 151 max: 170). so from what I can tell, the headgasket is not leaking, so for now i ruled that out.

what else could i possibly test? i cannot figure out why it ran fine for a couple days with no heating issues, and all the sudden the whole system seems screwed.

another thing: I have the heater on high when trying to bleed, and the heater is blowing hot air...so there has to be some sort of circulation.

so now my only thought is that since the lower radiator hose is not hot at all, maybe the thermostat is bad, even tho it opened in boiling water?

I cant figure out what the hell is going on for the life of me...been trying to figure it out for 3 days now. Thanks guys.

 

Did you remove the burp hole screw and fill the system untill water came out of the burp hole? ( burp hole screw is located on the intake where the upper radiator hose connects to the intake.)

 

sorry, forgot to put that. yes I did.

 

umm, try jacking the front up when you bleed. also make sure the thermostats isnt blocked or wedged in so it can open. last thing id check: take off the cap and start the car. see if the water moves when it gets hotter. if not its probably your water pump.

 

well, i did swap water pumps. no change. so tonight im going to take out the thermostat completely just to see if i get circulation. if the water moves then, that tells me bad thermostat.

 

like re037 said, tkae off the rad cap, start the car cold, and then wait until it getsvup to about where it usually is on the temp gauge and then look and see if the fluid is flowing, if not and you have already replaced your pump, then its probably your thermostat..just go buy a cheap thermostat from autozone or whatever to see if it fixes it, and if so then you could always buy a nice one like nismo or billion.

 

then again there is the possibility of a stopped up radiator... it does not take much to stop one up... material from when you scraped off the old head gasket could have gotten into the water passages and plugged the radiator a little or a lot... if the thermostat removal does not work i would suggest having the radiator boiled and cleaned... 45 bucks here at a radiator shop and they usually make it as good as new for you...