howdy

engine temps creeping pretty high at idle (not all the time). soon as i start moving it comes back down. cabin air heat also drops while at idle. water pump or thermo?

thanks

 

Have you recently replaced the coolant? Have you done a used oil analysis since the problem started?

Pull the cap and smell the coolant. Maybe it is due.

 

Your radiator probably has a hairline crack in it. Go rent a free pressure tester from autozone. These cars are old and have plastic radiators. They live under the hood where its very hot and thus theyre very brittle now and any bump can cause a leak.

 

The same thing happened to me a couple of months ago. 06 Coupe 47k miles. A friend of mine is an Infiniti tech, I was overheated on the side of the road so I gave him a call. He had me feel the upper and lower rad hoses for a drastic temp difference. And there was. He told me to turn on the heater full blast and drive to the dealership, (which was only about three miles away). We replaced the thermostat, overheating issue solved. Hope this helps you.

 

The fact that your cabin heat temps drop at idle tells me that it is not the thermostat, since the heater core flow completely bypasses the thermostat (ref: FSM page CO-2, it should flow the same whether the stat is open or closed), so it would seem that the water pump would be the more likely suspect then. I haven't heard any reports of water pumps going out on these though, but they are aging so I guess it's possible. If your noticing of the heater temps dropping at idle was just a fluke or a misinterpretation, then yes, I'd be looking for a thermostat or an inoperative fan, both of which are easily verified.

If you start the car when it is cold, and then feel during the first 5 minutes (or so) whether the upper radiator hose gets too hot to hold or not (i.e. coolant flowing through radiator), you can tell if the thermostat is opening at all. Also, you can see and hear when the fans kick on or not after the coolant start flowing through the radiator. They won't come on right away; it should take a few minutes after coolant flows through the radiator.

Good luck and let us know what you find either way.

BTW, it is always a good idea to replace the radiator cap too. It plays such an integral part in the cooling system (by maintaining proper pressure), but it is often overlooked/neglected. They are a wear item and should be replaced periodically.