Is my Thermostat bad ?

[turbotaone]

My car usually runs between 160 to 170 degrees, but once
in a while the temperature goes up to around 240, like when
I'm sitting in a drive-thru line or waiting in traffic. It only does
it now and then, but the last time that it happened I turned
on the heater to try and bring the temperature down and I
noticed that it was blowing luke warm air and the gauge was
showing 220 degrees. Is this my thermostat going bad ?

Thanks James

[1badTTA]

Sure your Headgaskets are good? I had one blow out after I was seeing the same thing you are seeing. Do a compresion test with the rad cap off and engine warm, it will show a leak into the coolant passage.

Hopefully that isn't the problem, you should also check to see if your fans are coming on when they should. If you are running an emmisions style chip, it may have the fans set to a rather high temp to get the engine hot for emissions. Had that problem with my thumbwheel chip (I didn't order it so I don't know what each setting is for)

You probably have a pocket of air in the coolant that you need to get rid of also, run the car at temp with the rad cap off and heater on, also helps to be parked up hill.

If all that doesn't help, I would go ahead and replace the thermostat and flush the cooling system really good.

[tta583]

The compression check is a good thought, just in case. I would expect, however, that you would have some other symptoms and that it would always overheat, not just from time to time. Never knwo, however.

I would do as 1bad mentioned and double check the fans and make sure you are full of coolant. 2 stories on myself here. I had a older Formula with a heater hose leak, a little pin hole deal. I was low on choices and had to drive it a distance till I could fix it. When it got low enough the temp sender was exposed to HOT air, not coolant. The gauge would about peg itself. Add more water, and it would drop down to normal. No "excess" block heat, just super heated air. Second, had an old Ranger a few yeard back. The last winter I had it the heater was luke warm at best. At a stop you could goose it a little and hear the whoosh then the heater would work well for a few minutes. Long and short, low on coolent, air bubble in the heater core.

Brent

[turbotaone]

Thanks Guys, I'm going to take a look at it tonight.