Van overheating

Hi, we have a 2003 Chevy Venture van. Apparently the good folks at GM decided that it would be a great idea to engineer this van so cheap parts (such as the thermostat) would require removal of half of the car to get at.

Now that I’m done ranting, I’ll tell you what I know, and hopefully I can get some help!

Our van had been leaking coolant for a while and we just got the water pump replaced, which fixed the coolant leak. We didn’t do anything silly like throw Bar’s Leaks in there, but we did keep it topped up with Dex-cool (What a wonderful invention! ). A few days later, we drove about 5-10 miles on the interstate, with no problems. I exited on the right, that looped back around over the interstate, and as I did, the temperature gauge spiked. We got to a safe spot and turned off the van and waited for 5-10 minutes (it was about freezing at this point). I thought the fix didn’t take and that the coolant leaked all out - but no dice, there was no coolant under the van, and the reservoir was full. Next time I tried adding coolant to the radiator it started to spill over almost immediately.

But the van still overheats after about 7-10 miles, even at 52F driving at highway speeds.

With the heater on full blast sometimes it would blow hot air, sometimes cold. When it blew hot air the temperature gauge would go down, though sometimes it would go down even when the heater was blowing cold.

When I stopped to check, the radiator was cold to the touch (not even mildly warm), though the return hose was hot - I had to pull my hand off within a second or two.

Our initial thought is that it might be the thermostat, but due to the engineering mentioned in my rant, the thermostat is located under the throttle body, behind the engine - not a quick fix for a $10 part.

I think that’s all the information I have - does it sound like a thermostat problem, or something else like a clogged radiator?

Thanks for any advice!

There could be air in the cooling system. It should have been bled out when the water pump was replaced, but sometimes it doesn’t get done properly and an air pocket remains.

This would also explain the lack of heat. If there’s air in the heater core instead of coolant you won’t get any heat.

It sounds like the coolant is not circulating. It sounds like you changed the T-stat as a “fix” when perhaps the problem was elsewhere in the system.

Since the water pump and T-stat have been changed, the possibilities that come to mind are a clogged radiator, a collapsed inner liner in a hose, an sir pocket, and (since you mentioned cold weather) perhaps an ice blockage still existing from water resting somewhere from the prior work (I’ve never heard of this, but it cam eto mind anyway).

I’d suggest starting by flow checking the radiator and the engine with hoses. Perhaps I’d test the hoses in hot water to see of the inner liner is collapsing.

Another test you’ll want to do, sincethe engine has been repeatedly overheated, is a compression leakdown test. There’s a very good chance that you’ve blown a headgasket. That may be your single biggest problem.

If the upper radiator hose is getting hot then the t-stat is probably working. If the upper hose is hot and radiator is not then the radiator is probably clogged. Yes the t-stat is an enormous PITA so its not something you just change out on a guess.

You do want to worry about the air. You should have a couple of bleeder screws to work with, though that system should actually bleed itself of air given the overflow design.

But the cool radiator is a pretty big top off. Don’t be afraid to change over from DexCool. I have an '00 Silhouette that’s been on universal coolant very happily for a couple of years & 20K miles or so.