2005 GM 3.4L overheat issue

[John Williams]

Hello, I have a 2005 Chevy Venture with the 3.4L and 225K miles on the clock. While driving down the highway yesterday the temp gauge started climbing very slowly but definitely above normal, I kept a close eye on it but after another 20 miles it was way above the normal range ( rough guessing I say around 220 Degrees F ), so I pulled over to look things over and I noticed that the upper radiator was extremely hot while the lower hose was cold. I let the vehicle cool off for an hour and drove it 30 more miles home with the temp gauge staying in the normal range. I know that a stuck thermostat should show the opposite hose temps than what I had found but didn't know what else to do so I went ahead and changed out the thermostat . I have since put about 20 miles on the vehicle and things seem normal so far with both upper and lower hoses being close to same temp. I am not 100% convinced that the thermostat was the issue as I tested the old one in a pan on the stove and it operated fine and opened at the correct temp. I was possibly thinking a head gasket but the vehicle never loses coolant and while idling I see no bubbles in the coolant and the system doesn't over pressurize. After the thermostat replacement I did pressure test the system and it held 15 Psi for about 45 minutes.
I am looking for thoughts on other possible issues I need to check or does the stuck thermostat theory make sense??

 

[TollKeeper]

The 3.4/3400 Can blow a head gasket, and not lose coolant.

The 3400 is a weird beast in that in can blow a head gasket, and run for another 30k miles.

2 things are the biggest problems with the 3400 cooling system, before you dive into the head gasket.

Making sure you are using a good, name brand, thermostat.
When replacing the thermostat (and if it comes to it, the head gasket), you vacuum fill the system. Differing parts if the cooling system are above the bleeder nipples. So it can be very difficult to bleed it correctly.

 

[John Williams]

The 3.4/3400 Can blow a head gasket, and not lose coolant.

The 3400 is a weird beast in that in can blow a head gasket, and run for another 30k miles.

2 things are the biggest problems with the 3400 cooling system, before you dive into the head gasket.

Making sure you are using a good, name brand, thermostat.
When replacing the thermostat (and if it comes to it, the head gasket), you vacuum fill the system. Differing parts if the cooling system are above the bleeder nipples. So it can be very difficult to bleed it correctly.

Thank you for the tips. Im all about quality parts and wanted to use an AC Delco thermostat but couldn't find one one quickly so I put in the best one Napa had. I ran the vehicle around town today for a couple of hours including some Highway miles and all seemed normal but Im still a little skeptical.

 

[TollKeeper]

If everything is running good for now, just keep going, but keep an eye on it.

The 3400 does not like running hot, ever.

So if no damage was done, than you should be good.

 

[John Williams]

If everything is running good for now, just keep going, but keep an eye on it.

The 3400 does not like running hot, ever.

So if no damage was done, than you should be good.

Thanks for your help and solid advice, I really appreciate it.
I've got 50ish Miles on it now since the repair and all seems normal so far.

 

[mrrsm]

Another Excellent Forum dedicated to Everything Under The Sun about GM-GMC 60 Degree V6 Motors:

60º V6 Family Tree - 60DegreeV6.com

This is the top level CMS page that shows all categories that hold the articles on this site

www.60degreev6.com

 

[John Williams]

Another Excellent Forum dedicated to Everything Under The Sun about GM-GMC 60 Degree V6 Motors:

60º V6 Family Tree - 60DegreeV6.com

This is the top level CMS page that shows all categories that hold the articles on this site

www.60degreev6.com

Thanks for the tip, I'll definitely check them out as I'm still running around with a couple vehicles with this same engine.
I came to this site first as I've had really great help from some of the folks here in the past.