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Old 08-19-2000, 01:23 AM
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RunningTooHot RunningTooHot is offline
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Join Date: Aug 2000
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First, I want to thank all of you guys (and gals ?) for your help! This site is GREAT. I hope that I may be able to contribute in the future, but for now I have a problem / question.

I have a 1980 450 SL (US spec, about 240,000 miles - never had the heads off) that runs way too hot. It has a new thermostat (First thing I checked, but I still have the same problem). The fan clutch is working properly (it disengages at about 3000 rpm). The coolant temperature sender is good (I checked it against the one in my other 450). The belts & hoses are good. I am running a 50/50 mix of Havoline extended life coolant (no aluminum radiator to worry about).

I just flushed the system to make sure that the internal surfaces are as clean as possible (for good heat transfer) and the flushing agent came out perfectly clean – there is no rust (the car has been meticulously, no, make that FANATICALLY maintained its entire life). What came to light in the process of flushing it was this: Even when it was being fed cool water directly into the radiator, the temp gauge still read just above 100 degrees (centigrade, obviously)!? I don’t get it – And yes, the new thermostat works (I checked it in a pot of boiling water, with a thermometer.

The gauge is reading accurately, as the auxiliary fan comes on at the proper temperature (as read on the gauge), and it runs at about 82-83 in the mornings, once it is initially warmed up, but before the heat really builds up – then it goes up, up, and away.

The water pump is putting out a good volume of water flow, and the top of the radiator does get very hot to the touch. It feels like the air coming off the fan is warm, so there is heat transfer taking place (maybe not enough?). I am completely out of ideas. Well, except one – is there a possibility that an air bubble in might be causing the temperature sender to read too high? And if so, (but it seems unlikely) how do I alleviate the problem? I have never had this problem before, and I have changed the coolant many times before. Plus, this problem just arose spontaneously, before I even flushed the system. (I flushed it Because of the problem).

I thought that I knew a fair amount about auto mechanicals, but now I’m feeling pretty dumb & helpless. I hope that someone might be able to clue me in.

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