Montanna Overheating

[studentmechanic]

I have 2 pontiac montannas that are doing the same thing. One is a 2000 and the other is a 2002. On the 2002 I replaced the lower intakes and they were blown. On the 2000 I replaced the thermostat. Now both of them will overheat when I drive down the road. If I park them in the shop just idling they will heat up to normal and throw warm air out the heater but as soon as I take them out on the road the temp will begin to fluctuate and within 1 mile they will be overheating. If anyone could help I would be so thankfull! Thanks alot, Matt

[LMP]

BLown head gaskets. SOrry for that. You have listed all the symptoms.
Intake gasket problem on the 3.4 is in addition to the head gasket problem.
Common.

[Judysvan]

126,000 mi have not replaced intake gaskets yet. It does lose about a cup of coolant a month, but thankfully not into the crankcase. Have replaced the thermostat and water pump at 80k. After start + about 7 miles, the temp gage goes right up to 210, then drops back to about 160-170 degrees (middle temp mark between 100 and 210). You might try to make sure the t-stat is not sticking or the waterpump is still pumping.

[drgrac3134]

I have a 99 montana with 125,000 miles on it but mine is doing the opposite. When let iddle to warm up then drive the temp guage will go to 210 or higher. If I bleed the air out on the thermostat housing it seems to work fine after that. If I just start and go no problems at all. I was wondering if the water pump might be going out? I dont know if that would cause air pockets inthe cooling system or not? Doesn't use much if any coolant.

[rockwood84]

i have seen the dexcool sludge up the waterpump so bad it can't pump as the blades are full. check this ......also do not put a t-stat made in mexico in as they won't open.