617 Engine Temperatures
 

Around August of 2006 I replaced the thermostat on my beloved 1985 300D. After the new thermostat the temperature gage would stay just below 90C.

At the end of December I replaced the radiator and thermostat on my 1981 300D. The radiator that I installed was not new, however, the core was very clean on the outside and as much as can be seen on the inside was as good as a re-core. The day after I drove this car on a local bypass and I kept the speed at 70-75 for about 30 minutes. The temperature ran around 95C. The next day I was on an interstate at the same speeds the temperature was again around 95C. (When I filled the mpg was 27.0!) In my day to day driving (25-55 zones) I have noticed that the temperature is 90-95C. These engine temperatures are in ambient temperatures of 30-45F. My concern is if I am likely to have engine temperature problems when it gets warmer.

Any thoughts, experience, or words of wisdom would be appreciated.

I used to take my temp guage very seriously.

Now that I've had several of these cars and read tons of posts, I just allow for the guages to be off. I've never had one overheat and I've had guages reading well into the danger zones.

15, 123's later, I just don't trust the guage, but I do trust the indestructible 617's

diesel don

my 617 right now stays around 100C no matter what and I tend not to believe it either...FWIW I have a new thermostat in hand and am waiting to replace it.

is there a definitive way to test that temp readout?

I bought a cheap meat thermometer from Wal-Mart I stick in the fins of the radiator..... or you could try something more modern like an IR laser reader. these are pretty cheap now. I saw one on the counter at Pep Boys for around $40.

is the temperature taken from somewhere on/in the radiator? Would it be fair to stick a thermocouple between the fins?

The most accurate way I know of is to replace the factory sending unit which is in the block and has contact with flowing coolant with an aftermarket one which is calibrated. Sometimes they come with adapters and you can make everything fit with out much modification. A good temp. aftermarket guage with sender is not very expensive and will give you a absolute temperature within a few degrees.

One thing that is good about the 'new' temps. on my 1981 is the MPG at highway speed.:D

It would be close in the fins of the radiator but the best place is in the block and in the coolant. That is where you really care about the temperature so you can pull over before engine damage occurs.

Mine reads around 90 C usually but has gone up to 110 C on a hot day.

replaced the leaking rad and temps rose 10°C
replaced the encrusted temp sender and they dropped 10°
??

Just for your peace of mind, try changing the VDO temp sender and also check the earth of the vehicle, these two have been known to give heartburns on these vehicles from time to time.

Thermostat
 

For you folks who are unfamiliar with British English......Earth is Ground in American English.......makes sense though, block ground would have an effect on the reading of the Temperature sensor.....

I just changed my Thermostat a couple of days ago......because I had begun to notice that my temperatures were increasing from a base of 95 C about 4-5 degrees or so when going up a long hill.......I paid high dollar for an official MB part from the dealership, because I wanted to know, absolutely that my thermostat would be operating in it's proper temperature range......now car runs at 90 C, but still fluctuates when going up a long hill.....

SB

Changing out thermostat
 

Just in case you haven't access to MB shop manuals......and if you have a factory thermostat......there is a little arrow stamped into the thermostat, around the edge.......this arrow points up......

The Thermostat that I removed was manufactured by MotoRad of West Germany.....and it did/does not have the arrow.......

The new one is part # A 617 200 18 15.....and it does have the arrow......

SB

This makes a lot of sense. I think my car has some funky electrical issues anyway. Will do this. Thank you. Does the speedo work electrically as well, or is it purely mechanical?

Shorebilly - Thank you for the tip. I got the Behr tstat from Phil. is that what you got from MB as OE?

dd

Don't know for sure.....
 

The OEM part had a BBE (I think) mark on it......bid not say Behr or any other company that I am familiar with......did have the star and the part number stamped into it......cost me $25.00:eek: and because I decided to do this project to the MB spec....I also paid $19.50/gallon for MB antifreeze.....have not added the new antifreeze....yet.....am still flushing the old, improper, green stuff from the system......need to run over to the dealership and get a new radiator drain plug, today......old one broke, partially......it's plastic with an "O" ring.......still works, but I want to feel secure......so I have filled, run the car, and drained the radiator 2 x so far.....when I do refill with the proper antifreeze, I will use distilled water to top up.....my well water has a good bit of calcium in it, and is mildly alkaline......

SB