Overheating problem

Our 2001 Montana, 3.4 lit. has been overheating recently, pulled over, checked upper rad hose, it was hot, lower rad hose cool, fans working, changed thermostat (what a job!!! @#$%) bleed the system, drove for a day and a half no problems, then it re-occured, could it be a blocked rad, water pump or cracked head? Is there any way to check or test to see exactly what needs replacing? Any input would be much appreciated, we like the darn thing!:confused:

Did you properly bleed air out of system after t-stat change?

Yes, we parked it on a slope to allow all the air to rise to the top, kept bleeding them out until there was no signs of air left.

Thanks,

So when you said you bled the system, you actually turned the little screws to release air right? If you start your vehicle in the driveway, A/C off and open the hood and just let it run, all the time keeping your eye on the temp guage inside, do your cooling fans kick on when the temp gets up around 12 or 1 oclock? (I'm assuming the guage is like it is on the 1998). If your fans never turn on, there is a problem there. Turn on your A/C and see if they turn on then. If they do turn on, is the air coming off of them hot? You said that the upper hose was hot and the lower hose cool. This to me means that the radiator is cooling all that goes through it. But it might not be much flow. That would point to your thermostat, which you just changed. What do you see that tells you it's overheating. How's your trans fluid look? How about your engine oil?

The overflow container has bubbles coming out of it, the engine oil is not creamy, normal. When the engine overheats, the gauge climbs very quickly to the top, and the computer light comes on(high temp), there is no loss of dex-coolant, heater works, and fans kick-in after it passes half-way on the gauge, where it should. Transmission fluid is good as well. Just not sure where to go from here. Hope this extra info. helps, thanks.

I just replied to your other post. If your oil is clean and you're not losing coolant, you probably don't have a bad head or head gasket. I think you don't have all of the air blead out of the cooling system. There is a tool ($$)that can be purchased that draws a vacuum on the cooling system and then fills the system when it is under a vacuum. Using that method there is no place for the trapped air to hide. These vehicles are known to be very hard to bleed under normal circumstances. Air gets trapped in the heater core which is higher than the rest of the system. I would put forth a concerted effort to bleed the system once again to see if you can get the air out. I would say that having the van on an incline may not help with bleeding since that would then put the bleed ports at an odd angle. The bleed ports were designed to be used on a level surface.

BE Careful. We had similair issue and had to rplace the entire engine. The thermostat quits working and the engine block cracks. It is a common problem with the Montana and there is current litigation I believe.

By the way, it is a PAIN to replace the thermostat.

gameman73, I think you mean head cracked, not engine block. There is no common problem with the block cracking on the 3.1 or 3.4 engines. There are known issues with lower intake manifold gaskets and a much smaller percentage of head gasket failures. If you let the intake manifold gasket leak go for too long it can lead to a head gasket failure which can cause a severe overheat and possibly a cracked or warped head.

another thing is was the t-stat you put in made in usa or made in mexico. if it was made in mexico then it ain't opening. been there done that. you can take 25 t-stats made in mexico and drop them in boiling hot water and two of them might open then again all 25 might not open.if the temp just keeps climbing then it sounds like a mexican t-stat.and when you use the bleeders to bleed air out with the heater on then drive it a day then bleed again.

We took the engine apart, 2 cracked heads and prestone was all over the engine, one of the cracks reduced compression and the other was overheating. Many thought we were crazy doing this job ourselves, all we've spent so far on 2 rebuilt heads, gaskets (set) and bolts, $1100.00, we had a few estimates done before we decided what we were going to do, anywhere from $2000, to $3000, so it made more sense that we try ourselves, good thing my husband knows quite a bit of mechanics, he purchased the Haynes book, and the garage that sold us the re-built heads included all the specs and the torque wrench we needed. It is now warrantied for a year, don't think we'll ever buy another 3.4 after this one.

PS: almost all together now, we'll give you an update :)

Thanks to all those who replied to this thread, all the input really helped!