On my 95 945 with 75k miles... I have noticed low temp on temp guage that has always measured in the middle. The car performance is normal so I suspect temp coolant sensor is ok. Heat is ok although not quite as hot as usual. 5 months ago I changed the hoses and heater control valve but the thermostat is the original. I assume this is a bad thermostat.. If so any "pearls" on what not do when replacing it?? Ill check the Faqs on this also. Thanks JOHN. Oh could a faulty heater contol valve give an abnormally low temp reading on the guage?? Thanks JOHN

Yes - probably the stat. They tend to fail "safe", ie: in the open position so the engine is overcooled. Proof will be a merely warm upper rad hose after the engine has gone a few miles on a cool day. A problem with the heater control valve would not affect engine temp. The standard stat for 940 non-turbos is 92C and for turbos it's 87C. Available from FCP Groton on the web for about $8 with new sealing ring. When replacing, look closely at the machined recess in the cylinder head where the sealing ring (gasket) seats, and make sure it is completely clear of scale and crud or you will have leaks.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

I bought it and received it from FCP today. They sold me an 88 degree #273459
Vernier for my non turbo 95 945. Sounds like they sold me the wrong one. Any problem with using this one?? close enough?? JOHN

This is the one for turbos but will work OK (ie: close enough) on yours.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

I agree with the others that it is a stuck open or broken thermostat. When you buy the new one, be sure to get a new rubber sealer ring which sometimes has to be purchased separately. When you put in the new thermostat, be sure the little air bleeder valve is in the up position. The FAQs show this clearly, take a look at them. BTDT

My bet would be on a thermostat that is opening too soon or sticking open. I've had terrible luck with thermostats for the last couple years for just this problem. Seems like both my Volvo and the wife's BMW only lasted a little over a year. PITA!
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'96 965 with 16' wheels at 110K. Had '85 745 Turbo Diesel for 200K.

You could measure the resistance of the coolant temp sensor and compare it with the resistance table.

32ºF - 7300 Ohms; 68ºF - 2800 Ohms; 176ºF - 300 Ohms; 212ºF - 150 Ohms.

You could also clip lead a 150 Ohm resistor in to the harness side while you're there and see if the gauge reads about 5/8ths full scale as it should.

By that time you should know if the problem is the thermostat or not. Replacing the thermostat every couple of years is still a good idea in any event. You might do it while you're checking the sensor/gauge function as it is right there.

Sounds like a stuck open thermostat to me. Been there done this one..
JJ