so i am now the proud owner of '94 90cs quattro. when i got the car, i had the dealer replace water pump, timing belt, tensioners, and the thermostat. I had noticed on the test drive that the temp guage never went above cold while driving. if the car sat and idled, the temp would rise and the fans would turn on. and the heat worked just fine. so most of the cooling system seemed to work ok. now that there is a new thermostat, the temp now rises to the first mark above cold, but still seems a little low. is this normal, and if not what should i look for? thanks for the help.

mike
1994 90 cs quattro

 

little mark or the 1st big mark?, which my seems to hang around the latter most of the time. if your air temps are low, or you're not driving far or being hard on it, then that sounds normal.

 

well there are three little marks right near c, then up a little is the first mark, then after that sort of a major one. mine is sitting at the first little mark after the three at cold. normal driving conditions....

 

during the summer with the a/c on and off. the outside temp really affects the engine temp since cooler air is coming into the engine compartment. i wouldn't worry about it being too low, just too high.

 

NORMAL....assuming air temps below 50F!!!

 

How to tell if your engine temperature is proper, is your real question. A working thermostat will keep the engine approximately 180 to 190 degrees, depending on which thermostat you've got installed, and this is the desirable operating temperature. This will happen, I think, regardless of outside temperature, including sub freezing weather, once you give the car time to warm up
Other than the gauge itself there are other ways to evaluate engine temperature
1 : when you idle, there's no movement of the car which will produce wind to cool off the radiator, so the engine and radiator temperature should rise as the radiator becomes hotter and hotter. The electric fan should turn on, since it is temperature controlled, and it will run until it cools off the radiator. The guage reading at the moment the fan turns on is the temperature that is a little too hot. Your desirable temp is a little lower than this reading
2: you can try touching the engine to see how hot it is after it's operated for a while. A properly hot engine will be much too hot to put your finger on, even for a moment.
3: the car heater should produce plenty of very warm air, if the engine is properly heated up .
In the summer, esp. w ac on, the engine will heat up a bit more, and the guage will rise a bit.
If you're vehicle passes these above tests, which indicate the engine is hot, I wouldn't pay too much attention to where on the gauge the needle is pointing, and probably your vehicle is fine.

 

If by "major" mark you mean the thick line pointing at about 11:30 or so, this is 90 degrees centigrade (C), or about 194 degrees Fahrenheit (F).

In looking at a diagram in the factory manual, the guage's thick line at the far left is 50C. Moving clockwise (or from C to H), the thick line is followed closely by the two other lines you are talking about.

The thin line which you call the "first mark" between the three at the far left of the display and the major mark at about 11:30 looks to be about 70C (or 158F), although the diagram in the factory manual does not label the mark.

The major mark at about 11:30, labeled as 90C, is followed by two minor marks, then another major mark at about 2:00, labeled as 120C (248F) in the diagram. I would assume, then, that the two minor marks are 100C and 110C.

When it's cold out (below 32F), my 93 90S would usually get close to but not go past the 90C mark if I was driving on the freeway or on other fast-moving roads. So I think what your car is doing is normal.

 

http://www.12v.org/maint/cc.html
51 Engine Coolant Temperature (ECT), in Celsiu