Overheating frustration

[elpiar]

I have intermittent over heating problem. I have done the following:

- New thermostat (twice!)- Waterpump 10k miles ago- Refilled and get rid of air using various methods (jack up the car, bleed screw, etc.)- Leak down test show no head gasket leak.

What should I do? how do water pumps fails?During over heating, if I step on the throttle a bit (in parking) raise up the rpm, the temp kinda go down a bit. So weird.

Help?

[94_240sx]

Did you touch both upper and lower hoses when car was running and thermostat was opened?

[elpiar]

Yes, everytime it overheats, the lower hose seems to be colder than it should be (when I'm not overheating). This is why I replaced the thermostat twice. The first one was autozone, this time it's the OEM nissan part.

What are some reasons that thermostat does not open other than failed unit?

[elpiar]

any other input?

[Ekinchheng]

Check your heater core, if the return hose is cold then the heater core is clogged. Is your carpet wet or moist? How's the heat when you turn it on

[SHIFTVAX]

Believe it or not the second thermostat might not be workin, is your coolant moving or setting still?

[elpiar]

i believe it's moving. cause most of the time, it works and i'm sure the water pump is working.

[elpiar]

Check your heater core, if the return hose is cold then the heater core is clogged. Is your carpet wet or moist? How's the heat when you turn it on

the return hose is cold-er, not cold. heat is good. i just put in radiator cleaner liquid. we'll see how it goes.

[24j0hn]

its probably the thermostat... ironically... thermostats are crap and are a hit and a miss... the thermostat is opening and closing randomly making the heat go up and down randomly.