85 300d cooling issues Help
 

the thermometer in the console indicated the engine was running consistantly at
100C. it was quick to heat up, ~5- 10 min to reach 100.
last thursday i replaced the thermostat with a behr 80C t stat.
took it for a road trip last weekend.
engine ran consistantly @ 90C on thermometer. occasionally it would rise just above 90 and then come back down. this was at speeds of ~70 -75 mph. it would also drop below 90 at times to maybe ~87. this is all assuming that the scale between 80 and 100 marks is evenly distributed.
what else can i look at to lower the T closer to 80, short of replacing the radiator. or is this good enough?
many thanks
cliff hubbard

Do you believe that the operating temperature should be the same as the thermostat rating?

Sounds fairly normal. The block is going to be warmer up around the head area anyways in my opinion and the temp sender is there. Also you might want to check that the gauge and sender are on the money by a thermal readout device if still concerned. Both are probably not quite new. Overall if it does not overheat on hot days I would be happy enough. We are not talking the temperature sensitive 603 engine here as well.

cliff,

FWIW I just replaced the t stat with a Behr one on my 82 300D that had the same symptoms as yours and my results are *exactly* the same as yours.

from what I have been reading here this is acceptable. I plan to do a citrus flush when the winter ends up here and Ill see if that affects temps.

but even as is Im not worried about it, as long as the temp stays consistent and doesnt spike.

dd

do you have good operating pressure? I found a bad expansion tank cap was a problem on mine, and a new cap (along with a replacement radiator) took care of mine.
John

the rubber on the cap of the expansion tank still seems pliable.
don't seem to loose any fluid anywhere, either.

Mine is consistently running 90-100C on the highway, by the dash gauge as well. I had opportunity recently to check it with an IR thermometer and it said 85 at the sender and 80 on the Tstat housing when the dash gauge was reading about 92. I'm breathing a little easier...

i think that most of these older benzes have inacurate dash guages, its bound to happen with heat and time...

Not to worry.....!!!
 

Your thermostat mixes hot water exiting the block with cool water from the radiator in order to supply water entering the block at 80*C.....after the water circulates through the engine it exits the block roughly 10*C higher than when it entered, or about 90*C......this is good!!!:D

If you have an MB Service Manual, see section 20-005 "Coolant Circuit and Engine Cooling"......this will give you a nice write up on how your cooling circuit works and what to expect from it....

And FWIW the Behr OEM Thermostats have a little arrow stamped into the edge ......this little arrow points up.....

SB

Where ya at??
 

I use the handle "Shorebilly" because I am from the Eastern Shore, originally.....my mom still lives in Berlin, and I visit several times annually.....next trip scheduled will be in June for the NASCAR Race in Dover....

SB