As some of you may know, I am an auto technician in St. Cloud. I am currently working on a customer'* 96 Bonneville N/A and he has the same issue that I have in my 94 N/A.

With the vehicle in gear, stopped (say, in traffic), and the A/C on, the car will overheat. It takes 10-15 minutes, but it does overheat eventually. I just replaced the thermostat in the '96 with a 180, I'm still running the 195 in my 94. It seems like this issue got better in my 94 after I replaced the lower intake gasket, but it'* tough to sell a $500 job to my customer without having some hard facts to convince him that replacing his intake gasket will solve the overheating problem.

Does anybody have any insight into this? I appreciate any prompt repsonses, either posted or PM'd to me. Thank you.

I love this forum. 10 minutes after my first post, I have a response with a lot of information. This is so much better than the DSM forum I used to frequent when I had my 95 Talon TSi AWD.

So anyways, back on topic:

I let the car get to 250 or so, then took it out and drove it, and the temperature slowly drops back down to the proper temperature. The issue only appears when the A/C is on so both fans are already running, and my 94 has a brand new water pump as of October and had this exact same issue in May of this year...seems hard to believe I'd have an impeller issue after 7 months.

I'm starting to think possible restricted radiator, but I'm open to any other ideas.

Assuming an unkown age on a water pump, I'd flow-test the radiator, and if it was good, consider changing the pump. There'* also the possibility of a thermostat not fully opening, and I've seen this happen before (more than once) on a new thermostat.

You're in an interesting situation, working on someone else'* car. You can't simply start drilling holes in thermostats and tricking cooling fans with a switch. Perhaps a full cooling system flush is in order? Imagine a blocked passage restricting flow in the heads. Perhaps from old thermostat housing gasket debris. Even a good pump and free-flowing radiator wouldn't be able to overcome a blocked passage.

You've got it wilwren -- when it'* somebody else'* car, your options are severly limited. If it were mine, I'd just start drilling and modifying electronics until I was satisfied.

I've recommended the next step for him is a full coolant backflush, and if that doesn't solve the problem, a new radiator. With the A/C on, those fans are pulling the heat from the condensor through the radiator. If the radiator isn't as efficient as it should be, the heat from the condensor is overwhelming the radiator, which leads to overheating.

We'll see where this one goes, I'll probably see him in a week or two for the same issue.

Thanks for all your help, and if you have any more suggestions, post 'em!

Since we're spending other peoples money here I'd like to charge him for a set of new radiator hoses and a new radiator cap(if that hasn't been done in awhile). I hope you resolve your customer'* issue(*).