Since the guage on a MBis in C,what is the acceptable running temp(summer) for a 83 300SD? Seems the guage is close to 120 C.....
Thanks in advance......BTW...the oil pressure as well mine is @ 3 (top of scale) when driving and stays @ 2 @ idle.......

The thermostat is rated for 87C so 120C is definately too hot. I'd be suspicious of the t-stat and radiator. The t-stat may be sticking and is the cheap easy to replace part so you should start by replacing it first. Given the age of the car it is very likely that the radiator is partially corroded and clogged internally. With a known good t-stat you can chek the raditor by feeling for cool spots right after a high speed drive with an immediate shut down.

If the car will cool down when running at high speed then you may have a failing fan clutch that isn't moving enough air when in stop and go traffic.

Maybe I shouldn't have said 120C it was firly close though. But since I just purchased it,I'll be checking what you suggested...forgot to mention,that was with the A/C on...if it matters......
Thankyou!!

That matters a great deal and changes the diagnosis...the question now is do the aux fan/s come on in front of the radiator when a/c is on ..and does the car NOT o-heat with a/c OFF ?????

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A Dalton

Will have to check & see...didn't hear the fans but looking is better than listening!! Thanks

The aux fans come on when the a/c high side presssure starts to climb up there...so, with no additional airflow to combat that extra thermal heat burden, the radiator gets passively heated from the a/c condenser and the engine o-heats..usually at low rpms or traffic.
Here is the switch that activates that circuit and there is a simple test I use to verify that circuit in the event that you do in fact find that you have no low fans w/ac ..

http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FG17RJ3A2FK1BPDOF&yearid=1983@@1983&makeid=MB@@MB@@X&modelid=300%2DSD%2D002@@300SD&catid=R@@Climate+Control&subcatid=R1055@@A%2FC+Temp%2E+Switch&mode=PA&subcatid=R1055@@A/C%20Temp.%20Switch&applicationid=000024786&source=www.peachparts.com&clientid=catalog.mercedesshop

You will notice that it is referred to as a temp sw , but in reality it is pressure sensor type sw and monitors the high side refrig pressure .
So, the test:
If you have no low fan w/ac On and a good hot ambient temp condition, you peel back the insulator sleeves on the pigtail end of that sw [ it is located at the reciever/drier ]. and jumper there with anything ...a screwdriver blade is fine... low fan/s should come ON ..if yes , the circuit is verified ...if NO, you have a fuse or relay problem ..or even a bad fan motor..
Now for the tricky part...
There is a time when the fan circuit passes the jumper test , but it still does not come on with the a/c on...the reason for this is usually b/c the a/c system is slightly low on refrigerant..not enought to trigger the fan,but still enough to give you a/c [ altough not max] ..so you wind up with no fan , a moderate a/c output, and an O-heated car....tricky diagnosis that fools many a seasoned guy. Just a few ounches light of refrigerant will bring on this condition, so something to watch for if your fans are not comng ON , but they do pass the jumper test..
Of course, you could also have a bad sw...but the refrig level is always the first suspect b/c they seep over time ... no matter what.

Check the fans.........

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A Dalton

Also change the temp sender, the VDO is notorious for going out of whack and make sure the ground connection is good on the car.

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