When I start my 300 SDL, it pegs all the the way and pretty much stays pegged! Is this normal? Plenty of oil in the car. Also the coolent light will come on for no reason every now and then. This is used engine in the car and it is not running hot at all. I think these are just quirks of a 20 year old car. Any thoughts?

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1987 300 SDL
Working on the engine!
It's up and running!

Pegged oil pressure gauge is normal. The oil pressure regulator is set at 7bar, the gauge only reads to 3.

Coolant light may mean the level is slightly low.

If the coolant level isn't low, clean the contacts of the level sensor in the reservoir.

Sixto
93 300SD 3.0

At idle, once the car has warmed up, the oil pressure should drop to about 1.5 bar. If it stays pegged you may have a sensor or gauge problem. My wife's '87 had a similar problem -- the gauge pegged as soon as the switch was turned on and stayed pegged. The sensor was bad.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
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"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

on my '80 sd it stays at 3 all the time. probably the blowby putting pressure on the gauge..? (the engine is really bad)

Blowby will not affect oil pressure.