Chevrolet Repair: Cooling Problem - 97 chevy Venture, coolant level, chevy venture

Question
Hi Van,

I have a problem with the cooling system in my 97 venture. Normally the cooling system works just fine, keeping the temperature gauge at 1 o'clock position. That's normal behavior.

The problem is that sporadically, it just start overheating with the temperature close to the red line. Every time it happens, I check to see if the cooling is low(not the case, it's almost full) and I already replaced the thermostat but the problem seems to appear now and then.

Every time the engine start to overheat I turn on the heat to see if it helps, but the air coming from the heater is not hot at all, so I might think that the water is not flowing correctly.  When I'm lucky, the cooling system starts to work just fine after a few minutes driving.

The other weird thing is that the overflow thank is almost allways receiving water, is it normal? Sometimes it gets full and actually looses some coolant, not much actually.

What should I check besides the thermostat that was already replaced (about one month ago)?

Why can this happen so sporadically and sometimes get fixed without any intervention?

Why when it's overheting the heater system stops working too (blowing only cool air) and when there is no overheating problem the heater is working normal?


Thanks in advance,  

Answer
Hello Juancarlos,
Sounds like the thermostat is sticking, or the water pump is not working.
Since you have replaced the thermostat, that just about narrows it down to the pump.
I have seen impellers come loose on the pump shaft.

I assume you have checked the coolant level in the radiator, and not just the recovery tank?

If your water pump is good, something else is restricting coolant flow, but even if the radiator is completely plugged up, I would expect enough coolant to circulate to operate the heater, so therefore I would suspect the pump, or the drive belt is way too loose.

Van