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Finally got the 77 out for a shake-down this morning to go to the grocery store. It seems to like to run between the 3/4 mark and the red mark. I have a fresh single pole sensor in it, not the one from the 89 donor. I ran the heat to keep it from getting hotter, lots of warm air. I believe I even re-cored radiator a few years back so that should be good. I have a spare manual transmission model to try. Aside from the possibility of a bad stat, were there different ranges of single post temp sensors that could be tripping me up?

Ron,

I watched the BMW dealer use an infrared thermometer to compare the temperatures of the upper and lower radiator hoses to diagnose a faulty radiator and thermostat on my 540. Have no idea if consumer versions are accurate but seems like a good tool to help in situations like yours.

My 81 has 2 sensors. One for the dash guage and one for the fuel injection. You could get the car warm, and use a dvom to meter the Jetronic one. There is a data sheet on page two of this link. http://www.bosch-motorsport.com/media/c ... 739pdf.pdf

How new is your fan clutch?

My car, has a bad fan clutch. 70 degree day stop and go traffic I surpass the 3/4 mark. I also know the Thermostat was removed by P.O. to maximize the Cooling, which in hindsight can allow the coolant to pass through the radiator too fast and not cool as effectively.

All winter has sucked without the thermostat (car never got into closed loop on days below 40), but did still produce enough heat to be comfortable in the car. I'm wanting to throw one in and get an electric fan kit soon.

I think you'd want to make sure that it's really running that hot or if it is an issue with the sensor. There are a lot of subtle way to get tripped up. One non-obvious one is that there are at least two different versions of the thermostat (aside from the temperature spec) that seem to correspond to new/older versions of the thermostat housing casting.

Borrowed the temp tool from the shop after having the radiator tested, it was fine. Turned out the thermostat was stuck shut from being dry for 5 years. I popped it free and now everything seems to run a lot cooler. 180 at the neck now.

Just need to get the Hc levels a little higher to cool the exhaust down.