Coolant temp is not moving from 40* on the dash. If i ground out the sender wire, the dash gauges pegs to "full hot." I assume this is expected behavior and i simply have a bad sending unit?

Thanks!
Alex

What are you working on? It is always at 40 when the wire is connected or it never goes above 40?

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

300TD. Needle hovers around 40* while driving (outside temp around 10c.

Although, I did a bit more investigation with an infrared thermometer and head temperatures are staying around 45-50c, so I am thinking I may actually have a stuck open thermostat. Plan to remove the temp sender and stick it in a cup of hot water to isolate the issue.

If it reads colder temps and only goes up to 40 the thermostat is bad...been there several times. The sending units have a rather low failure rate and thermostats have a higher failure rate.

__________________
"Rudeness is a weak man's imitation of strength" - Eric Hoffer

I replaced my sender unit and it did the trick. The old one was rusted up pretty badly. I guess it’s only brass plated, not solid brass, perhaps it’s some kind of bi-metal.

Mine also pegged full hot when I did the ground test.

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1986 300SDL, 362K
1984 300D, 138K