My coolant temp gauge seems to be locked at the 80C degree mark. It never seems to move. I replaced the coolant temp sensor (at the front of the head) and that did nothing. I suppose the thermostat could be stuck open, but even then, I would think the gauge should still move some as the engine warms up from totally cold to hot. Am I missing something? This is starting to worry me as I certainly want to know what my temps are!

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'81 300TD turbo <<sold 12/05 to another diesel nut

Sounds like it's gotcha worried!

Maybe there is nothing wrong at all with it and it is telling you the truth!

Anything is possible and guages can die, or give false info!

Wonder if you could take a temperature reading with a thermometer at the reservoir to confirm, or deny?

If I am reading your post correctly, the gauge stays at 80 even when the engine is dead cold, is that correct? If so, unless you live in Death Valley, I think the gauge is lying to you.

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Keep everything as simple as possible-but no simpler--Albert Einstein

I re-read his post and ya, it sounds like it is stuck at 80C! Not right! It should return to zero when cold!

That's right, the gauge always reads 80C, even when I first start the car in the morning. That wouldn't work even in Death Valley, because that translates to 176F.

Is there any common failure with this gauge or the wires feeding it? I've checked all my fuses and that isn't the issue. All the other gauges work.

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'81 300TD turbo <<sold 12/05 to another diesel nut

I'm well aware of the conversion. I figured assuming 130 degree ambient, full sunshine, black car, 176 may be attainable. Certainly wouldn't be outside the realm of possibility for the interior with no windows down.

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Keep everything as simple as possible-but no simpler--Albert Einstein

Pull the cluster (not too hard to do) and pull those gauges out and move it with your finger..... might just be stuck and that might loosen it up. You have to disconnect the speedo and the oil pressure line to pull the cluster out along with a couple lights for the brake and glow plugs, the tach and speed sensor thing on the speedo..... and of course the big plug for all the gauges on the left side. Sounds like a lot but just the speedo and oil line have to come off with it still in the dash. I just did this and it takes maybe 10 minutes at most.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

I took a close look at the gauge this morning and found that the gauge needle is dragging on the gauge face. Looks like the needle was bent by some ham-fisted fool maybe while reinstalling the gauge cluster. It's bent so bad, the needle's shaft is actually off kilter. So I gotta get in there somehow and unbend the needle and maybe my problem is fixed.

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'81 300TD turbo <<sold 12/05 to another diesel nut

....chuckling....I DO live in Death Valley, and my guage still starts at the bottom when 'cold'. Had our first 120 day yesterday. Won't be brushing teeth with cold water for a couple months. Benz seems to be running great...

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1983 300D- silver blue, tan leather, 205,000.
1975 Datsun 280Z. Stock, ready to restore.
1983 San Juan 23. Dry docked.

Fixed! I pulled the clear cover off the gauge cluster (it popped off really easy, dunno if that's normal) and bent the temp needle carefully away from the gauge face with a piece of paper. It bent into shape very easily and now swings free and seems to be reading temperature now! :p

Rhino: Glad you can laugh about that heat! I'm west of you in the Central Valley and we broke 100 the past two days. That's enough for me!

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'81 300TD turbo <<sold 12/05 to another diesel nut