JimV8

I replaced the rad as I was concerned that routinely the guage was sitting at the top white mark, except in really cool weather. I was in stop and go traffic last week, and the dial was way up so I hit the defrost button and magically the dial dropped to the second mark within 30 sec. I'm guessing that my thermostat is not opening properly?

TheMAXX

I am guessing that your thermal switch in the radiator is the problem and your fans aren’t turning on. But when you hit the defroster, which I assume, turns on the AC it forces the fans on. Thus cooling your car.

M758

This is actually normal. The last white line is like 210-215F or so. Not really that hot. In normal operatation the temp will increase to that point then the fans kick in and should lower the temp. The easiest way to hit that temp is to run on freeway at speed then come to stop light. The cool air at speed causes the fans to shut off and t-stat to close to maintain proper temp. When you stop the flow of cool air stops and temp increases. Once it hits this last white line the fans kick in and bring th temp down. Now anytime the A/C runs the fans turn on no mater the water temp.

If you exceed the white line and fans don't turn on you have a problem. Really the car "normal" range is between the two white lines on late gauge or between the first and last white lines on early 3 line gauge. Most new cars have dampers in the temp gauges designed to simple not move as many folks think and change in temp is bad thing. Really all cars run within a temp range an the actual temp fluctuates within this normal range. The cooling system is designed to keep it in that range, but keeping things at 190F all the time is near impossible. In 944 these gauges move as the real temp moves.

JimV8

Thanks Joe, that makes sense and I notice that the dial doesn't go higher than the top mark and, yes, thats when the fans come on. So I guess everything is AOK.

lleroyb

You might also still have a little air in the block (head).
Lou