85 300TDT engine temp is high with all new parts - Page 2 - PeachParts Mercedes-Benz Forum

tobybul · #1 09-17-2006, 11:21 AM

Quote:

Originally Posted by jrgslg

If you removed the thermostat for troubleshooting purposes would you be able to rule it out as a culprit ? You coud take the thermosat and put it in a pan of water then heat it up and then verify when it physically opens with a thermometer . I also have seen high temps at highspeeds caused by a bad lower radiator hose,the springs were damaged and allowed the lower hose to collapse and waterflow was restricted to the water pump (lots of money and parts were replaced instead of a 5 dollar hose).good luck,Johnny

Good point on the bad hoses... it does happen.... just replace them...

squaredealz · #2 09-23-2006, 08:18 PM

A replacement fan clutch dropped the temp down to normal range. When I shut off engine, old fan clutch spun a bit to long before stopping. Put one in from my donor car and that seems to have fixed the problem. Thanks for all the input & help.

stephenson · #3 09-23-2006, 08:48 PM

If it ran cool without a thermostat, but hot with a thermostat, why would a new fan make a difference? Thermostat sets the minimum temp, right? Without tstat no minimum temp, so runs cool ... add a tstat and runs hot ... but with new fan runs at tight temp?

After having a spate of bad thermostats in the early 1980s on a 2002 BMW, I learned from several of the BMW club that they consistently drilled small holes around the perimeter of the tstats disk (internally, of course :-)). I think the logic was that you allow some flow of warming water which helps the tstat open ... have done this consistently since then on most tstats - I suppose it will, as a side effect, slow the warm up cycle, initially?

Maki · #4 09-17-2006, 11:59 AM

I've had a couple temperature gauges in OM617.952 W123 diesels read 10 or 15 degrees high. Cleaning the grounding points didn't seem to help -- the gauges were just consistently off.

I had to repair the instrument circuit board on my '82 wagon last month and temporarily swapped clusters from my parts car. The temp gauge from the parts car indicated 95-100C while the original gage read 85-90.

The parts car was my daily driver before it got rear-ended a few years back, and it almost always registered an engine temperature of 100-105. As a test I once removed the EGR thermo switch from the front of the cylinder head after warming the car up (the pressure cap was loosened but even then the coolant surged out a little -- be careful) and put a candy thermometer into the water jacket. The thermometer read between 170 and 180 degrees, as I recall -- not the 212f (100c) indicated! So that's a poor man's infrared gauge for those who don't mind spilling a little coolant. JUST MAKE SURE THE COOLING SYSTEM ISN'T PRESSURIZED (pardon the caps). And wear rubber-coated work gloves to prevent parboiled fingers. I'm probaly stating the obvious, but playing around with hot coolant can be very dangerous

One more cooling system anecdote: I remember reading a theory on Rich Sexton's old mailing list by a guy who was convinced that the thermostat housings on 617 diesels could erode slightly at the thermostat bypass valve seat. The erosion, he theorized, allowed some coolant to bypass the radiator at all operating temperatures and thereby raised the engine temp to unhealthy levels.

His fix was to drill two or three holes into the outer ring of the thermostat. He claimed that it forced the thermostat to open wider and seal off the bypass circuit. I forget why he said it worked that way -- probably increased the flow of heated coolant through the stat -- but it's an interesting theory.