I posted about this in the diesel section, but this is not necessarily a diesel question but is a tech question/problem.

This morning There was a bit of ice on the windshield. We live in Atlanta so it wasnt much below 32F. I know folks drive these cars in really cold weather so i am thinking the car should get warm at this temperature.

At any rate the temperature gauge which has 5 marks, three of which have a designated number, never got above the second mark during my 65-70 mph drive through the city.

The marks are mark (100), mark (no designation), mark (175), mark (no designation), mark (250).

I think my thermostat must be stuck open. Or, is this normal?
Does anyone know what the temps should be for the temperature gauge? The marks aren't uniform space apart or I could venture a guess.

Is the second mark considered minimum operating temp?

Are there more than one thermostat temperature for this car?

 

Hi,
Can't rely on what the engine temperature guage says however I would expect the car to run circa 90C. MB's usually run with 5 C of this even on the guage.

Diesels emit much less heat than gasoline engines and therefore take "much" longer to reach NORMAL stabilised operating temperature. This is why many diesel cars in Europe have additional fuel burning or PTC heaters to complement the heat coming from the engine during the warm up stage. Once the car has warmed up...give it 5 mins on the highway at 60mph or so....your inside guage should be reading about 90C if the outside temp is only 0C. If not I suspect that it is NOT the thermostat because at this speed there should be sufficient heat coming from the engine that the thermostat should be open anyway.
If it is still running "cold" try placing a piece of cardboard in front of the radiator matrix and see what difference this makes BUT makesure it doesn't cause the engine to overheat should you forget to remove it for the Summer or start towing a caravan etc.

It is quite possible that your stat is stuck open but these things are pretty reliable.. If you conclude this is the problem you need to remove and place the termostat in a saucpan of water and measure the temp at which it opens as you warmup the water with a thermometer placed in the pan.

Of course the engine may be up to temperature but the electronic valve which lets HOT water to the heater matrix may not be functioning correctly. I believe this defaults to CLOSED in the absence of power.
0C shouldn't give you any real problems. Most European cars are now tested in Canada and Finland in temps as low as -40C....Just in case we get a real cold snap!
Stuart

 

Hello and thanks Snanceki.

Yeah I had a feeling this weather should not be a challenge to the car. I in fact did get some cardboard and cover about 2/3 of the radiator from the passenger side toward the driver side. I did not cover the oil cooler. The temp came up about half way between the second mark and the 175 mark last night and again this morning with the cardboard.

Since I have the cardboard in place and the gauge still indicates less than 175f I now wonder if I need another temerature sending unit.

I have found that if I turn the blower off and set the heat levers outward that I will have heat and defrost while the car is moving. When I get to a stop light I again have not heat and no defrost. If I then turn the defrost blower on I get cold air from the side and defrost. Is it possible the air direction gates within the dash are vacuum driven? If so I need to get a diagram of the vacuum connections.

Now I do see the water hoses that go through the firewall and I am assuming these are to the heater core(s). There are 2 valves and each is operated by a cable. Again I do have heat with out blower while in motion.

I was looking on the web for thermostats and I ran across something interesting. There is a wide range of temperatures for thermostats. From 174F-195F and a couple that were rated at 80 with no designation for celcius nor farenheit. I am thinking 80C which equals 176F.
So, following that the lowest thermostat setting is about 176F and I am not seeing even 175F per the gauge I think I have either a bad sensor or a bad thermostat. On a warmer day at about 60F ambient, I know the gauge went up to 175. Im betting the thermostat. I will open it up this weekend and see.

 

Quote....so i am thinking the car should get warm at this temperature.

Does the interior of the car get warm or is it just the guage that is worrying you?

If the inside gets nice and warm it is unlikely the thermostat.

 

Both, actually. At first I wasnt able to tell that there was any heat in the heater cores and because of this I began watching the temperature gauge closely.

Currently 1) I am not able to get forced warm air into the car, and, 2) I am concerned the operating tempurature indicated by the gauge is low.

Is there more than one fan? The fan will run when the AC **** is turned on a bit.

I have the owners manual and the heater/defroster is not working as described.

 

Afraid I'm getting a bit confused now and I don't have any specific knowledge of your model.

Modern cars have only one blower motor for both the heater and A/C.
Older cars often had two dependent upon whether the A/C was a simple add-on system (which many were back in 75) or an integrated part of the heater A/C unit.

All I can offer now is to check whether the pipes connecting to the heater matrix are HOT. Unless you have an electric thermometer it will be difficult to decide what is HOT. They should be sufficiently HOT to make it difficult to keep holding them (once the engine is warm). try to find a bit of the pipe which is metal rather than rubber. If they just feel just warm then the engine coolant is likely running cool and the engine temp guage may therefore be reading correctly.

Stuart.