My 1985 300D has some gauge problems that may or may not be causing the temp gauge to read ambormally hot. Untill i know for sure i need to trust that its right. When im cruising steady state at 80MPH the gauge gets as high as 106C! Is this correct? Where should this engine be running at? The radiator gets hot and its between -10 and -5C outside right now so i cant see why it wouldnt be able to shed its heat.

Well, 106C isn't where it should be. You should have a thermostat that starts to open at 80C and is fully open at about 94C. I would expect your "normal" temperature to be in the 80-85C range with cold ambient temperatures. Hopefully, you just have an instrument problem.

If the radiator gets hot but is not cooling then airflow path is likely obstructed by leaves, bugs and dirt in the fins.

Go to a carwash and use the pressure washer to blow out the radiator and A/C condenser. Be sure to wash it from both sides, not just the front.

Sounds like a bad radiator.

If your temp is lower when running at more sane speeds, then it's either external blockage as suggested above, or internal blockage.

T-stat problem would give you a high reading at speed or in town.

Should be in the 80-85C range, once warmed up.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles

Check your ground. Also replace your VDO sender if its old.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT

I suspect a radiator issue too. Feel the radiator at the top portion and the bottom portion after it is up to temperature. Is the heat evenly distributed?

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Jim

Fixed!

It was a bad ground in the cluster that was causing the temp and fuel to both read high.