Unexpected high heat on 300D

[cmac2012]

My car, ‘84 330D, 146k, has been running pretty well lately. I’ve had to fix numerous items, but miraculously the cruise control still works. It will pull very nicely up to 90, I’ve never tried to go past that, even going 90 is probably pushing it I would think.

I finally got my temperature gauge working. Combination new sensor and a better instrument cluster which coincidentally had 2k less than on the odometer than the original.

Last night I had a brush with mortality perhaps. On a 10 mile freeway trip, temp started going up a bit much. Same thing on the way home. I checked at midway, coolant and oil are both fine.

I’ve never overheated it, but this is how my blown head gasket behaved in my SDL about four years ago. In addition, I could swear I’m hearing a different noise, a slightly ragged note added to the mix.

One small item in my reality concerns me. I’m living in a charming, secluded house in Orinda, California. Not sure how a working stiff hippie like me landed in such an exclusive zone. Well, I am sure how it happened, but nonetheless, it’s a puzzle. The small problem is the driveway is rather steep, about 30 yards long.

The small road leading from the main arterial to our house is a gentle incline and aims right at the driveway - the street we are on approximately perpendicular to that stretch. I can’t build up any momentum on that one, so I usually take a right turn go up a quarter of a block, turn around then I have a slight down hill leading up to the driveway, I can get the RPMs up and cruise nicely up the incline.

Sometimes I avoid that step, if I hit it right, it will kick into the elusive granny gear and go up pretty good. Last night I tried that, and it would not go into granny, stayed in second (as God is my witness this is a four-speed tranny). It was lugging up the driveway. I’ve got to avoid that, can’t be good. Unlikely that it’s causing this overheating thing, but who knows.

[greazzer]

Did it come and go or did it stay higher than expected? That’s not super high. Have you tried driving around without a thermostat?

[cmac2012]

From above the midway point of both segments of the trip it stayed right around the hundred degree mark, I assume that mark is 100. The thermostat is perhaps 10-15 thousand miles old. That is a good question, I could try taking it out for awhile if the situation persists.

I was relieved that it didn’t go any higher, but the memory of my SDL is hard to ignore. It hovered around the same mark for about a week, and then started billowing steam, eventually dying completely.

This car is turning into a real gem. Still has numerous small problems, I don’t have vacuum door locking yet, I still shut the engine off with a Mityvac sitting on the floor in front of me. The heater motor fan assembly needs to be replaced, pretty sure, it’s making a hell of a racket, a thumping vibration. Other aches and pains, I could go on.

But the handling, the brakes, the engine and tranny are basically outstanding. I finally got good vacuum going to the brakes, I’ll seal the rest of the system soon enough. I have been getting optimistic, thinking I might have 100 K of really reliable driving ahead. And I still may. I’ll watch it closely. If indeed it comes down to being a head gasket, that’s not too daunting, I’d be willing to give it a shot.

There is one more issue that could use attention, it leaks oil and tranny fluid, enough to be a pain in the ass. Another PITA I would love to make some improvement with is being able to get the tranny to do what I want it to. I gather this is a common issue. I have read other people wondering why they cannot start off in first gear. I sporadically start in first gear.

[greazzer]

If you pull the thermostat the only real downside is no heat. Your oil canister’s thermostat is invariably seized. Without a thermostat you should never go over 60 C*

[Sugar Bear]

Quite likely a failing thermostat, I'd replace it. It would be good to confirm the operating temps with an infrared thermometer to confirm gauge accuracy.

[cmac2012]

Good advice. I am doing a work trip with my van right now, I’ll drive the Benz again in a few days. First off I’m going on take the thermostat out and see if there’s any change.

I recall Brian Carlton saying that if there was a way to make your engine run slightly hotter, it would be good. So who knows, maybe I should go with this. But on the other hand, I don’t like mysteries.

[87tdwagen]

I would recommend that you double check the gauge readings vs the Thermostat with an IR Temp reader to verify before pulling the T-stat.

Have you noticed this only at night, or is it the same during the day too? If it reads higher at night, you may want to check your gauge cluster's ground, or better yet add a new ground wire from the cluster to the chassis. Given your recent work with the temp sensor, wiring and cluster, this would be my first goto area for diagnostics just to be sure.

Best of luck in resolving.