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So I've got an oil pressure question. The operating envelope for pressure seems to match expectations on the board - always 3bar when on the gas, can drop to 2 bar at idle when stopped.

However, on longer drives (+1 hour), I sometimes get a fluctuating read, with a quick frequency, i.e. at idle fluctuating between 2.00 and 2.20 really fast. When it hits the stopper at 3 bar, it buzzes until I'm on enough throttle to pin it there.

It this likely a signal / sender problem (pressure gauge getting warm?), or a real fluctuation in my oil pressure. Anybody else seen this?

1984 300TD
 

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1985 300CD Turbo coupe, 2006 E320 CDI sedan
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It this likely a signal / sender problem (pressure gauge getting warm?), or a real fluctuation in my oil pressure. Anybody else seen this?

1984 300TD
Sounds like you're simply down a quart

//greg//
 

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W-1-2-3 Go!
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Do a search on oil pressure flickering. There was a topic on this and MB has a solution to insert a small "pin" in the oil line to dampen the pulsations.

Some have mentioned to remove the oil line and clean out the sending unit at the oil filter housing.
 

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Discussion Starter #4

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1984 300D
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If this was happening to me I would want to know what the Oil Pressure really was. This would require setting up a test Gauge. Unfortunately there is no easy way to set one up.

When I wanted to check my Oil Pressure I drilled a hole center top of the Oil filter Cap and tapped it for 1/8 inch pipe threads.
The drilling can be done by removing the long tube from the Oil Filter Cap. The tube is just pressed into the Cap.

The other way would be to use make an adapter fitting to screw into where the Oil Pressure Gauge Tubing connects at the bottom of the Oil Filter.

(Also there is a valve at the bottom of that tube that can stick. If that valve sticky it might cause that variation in Oil Pressure; you can blow air down the tube to clean it out.)
Oil Filter related. Might just change the Oil Filter (or do a complete Oil Change) and change the 2 O-rings at the bottom of the Oil Filter Tube to see if that corrects the problem.

If you have done the above stuff and the Oil Pressure is still fluctuating you could have an issue with the Oil Pressure Relief Valve in the Oil Pump.

Those are some of my thoughts.
 
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