Eric

I've noticed that my coolant indicator will rise if the truck sits at idle for more than a couple of minutes (it won't overheat in the time of a normal stoplight)

If the heater is on, when the temp starts to rise, the air blowing out of the HVAC will start to blow cold. This makes me think that the water pump is not moving enough water to cycle through the engine and Heat exchangers (radiator, heater cores)

Is this a common problem on 3.0's? are there other places to look besides the waterpump?

Juggalo

Have you recently changed you coolant? I remember when my 240SX did that after getting fresh coolant put in, because I had an air buble in the coolant. That could be it but there's plenty of other reasons as well.

Someone will chime in with better advice I'm sure

Eric

I've checked the coolant, but not changed it. are these systems real picky about pressure? I know on the RX7's there is a little dance that is involved in all the processes to put coolant in the car

MTL_4runner

It seems like these overheating problems may be due to a leaking headgasket (exh leaking into the coolant). This is not always the case but it seems to be a recurring theme on these 3.0 motors. It has been suggested to also put a T valve in to bleed the air out on a heater hose (ie open until full, then close).

Eric

I'll poke around with it today when I'm finished with work.

although I wouldn't rule out the head gasket, it was replaced in the last year. I didn't do the work, nor did I own the truck at the time, so I cannot comment on the work performed. what's the common practice on checking the HG? compression check? look for bubbles, or air comming from the coolant resivour tank?

mike_d

could it be something as simple as the fan not running? i know it doesn't explain why the heater would blow cold air, but i've had fan clutches go out and everything would be fine when driving because you get enough air in the radiator to keep it cool, but at stop lights it'd start heating up.

Nam

Sometimes it may be the case even though it has nothing to do with the "heater" problem!

Good luck,

Nam