hot but not overheated, now temp is 110: 83 300D
 

(Apology for duplication...I mistakenly placed this first in diesel performance section).

Hi forum friends. I've had great success here in the past, hoping for some new clues.

I have an 83 300d with 309K miles. Runs great (especially since fixing idle problem in December). Typical running temp is around 82-85c. For years.

This weekend, I had a quick drive from Norcal to SoCal. Checked all fluids in advance. Over the grapevine headed south on I5, car got hot. Almost 120, but not overheated. Then back down, but to about 110 and stayed there.

Next morning before driving back, checked fluids again...full coolant. Drove home on I5 (avg around 80 MPH), and mostly at night, with heat on and windows open to ensure no overheat. Made it back with the temp gauge at 110 the whole ride.

Now for the past 2 days, the "new normal" seems 110 v previous low 80s. Went here in the forum and saw ForcedInductions recommendation to clean radiator (done), and also did a coolant flush and oil change. Still running 110 or so. Was able to rev the car in the driveway with AC on full blast to get aux fan to come on at 115...which it did.

Any suggestions why car is running warmer or what next trouble shooting steps might be?

Thanks in advance, BD

Thank you Forced Induction...was hoping you would have responded.

So, after a quick drive this morning, temp was 100. Checked the radiator as you suggested and it's definitely hot.

In addition, on the drive, I also noticed the fuel gauge "flickering". Am now wondering if:

- problem is the instrument cluster connection for fuel/temp/oil psi
- fan clutch
- if not the thermostat, isn't there a separate coolant thermostat sensor that might be awry?
- some combination of all these things

problems solved!
 

A big thanks again to Forced Induction for all the insights with my tempature issues.

Here's the happy resolution, with my temp back to the "old normal" of 82-85c:

- replaced the fan clutch (was bad)
- replaced the thermostat (was also bad - and the original with "made in Germany" stamp)
- confirmed expansion tank cap is proper (already 140 rated)

As for the flickering of both fuel and temp on the cluster...it's a tight connection from behind the console. Since the flickering is relatively minor, and now that the temp issue is fixed, I'm going to kick this can down the road. Particularly since I fill my tank based on trip mileage rather than relying on the exactness of the fuel gauge. So, if I stumble on a cluster from an 82-84 300d, I'll address this then.

Not sure if the fan clutch/thermostat failure is related to the long drive, or just the age of the car.

In any event, I wanted to share this for fellow forum members who may have similar issues down stream.

Best to all, BD

More good news...I was able to find a left gauge cluster on Ebay. The seller didn't know what year MBZ this came from, but it looked right and was pretty inexpensive so i bought it. When the cluster arrived with an "85" stamp on the back side, I figured this was from an 85 300d. With the help of a friend who has the tool that releases the full instrument cluster from the dash, we replaced the left cluster this morning. And, the flicker on both the temp and fuel level are gone!