Oil Pressure lowers when car warms up

On my 190e, my oil pressure seems to go down as the car warms up. This I think seems to be a fairly new occurance. My car was somewhat overheating due to a bad water pump. I just recently replaced it and the car doesn't
overheat (stays around the 80-90 mark) but my oil pressure seems to go up & down. Oil level seems ok. What could this be?
Thanks
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It is normal, at any given engine speed, for the oil pressure to be lower when the engine is fully warmed up than when the engine is cold. Do you notice this at idle speed, or at all speeds?
If you believe the engine ran for any length of time at above normal temperatures, and you now have concerns about oil pressure, the first step would be to change the oil and oil filter if you think the oil was damaged or contaminated in any way.
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Ditto. Could just be that the motor oil is old and diluted. Also make sure the shop you take the car to uses the correct weight motor oil. A too thin an oil can easily cause your oil pressure to drop too far when it gets hot, and some of those quicky-lube places seem to have their own ideas about what oil to pour in, rather than what's actually specified in your owner's manual.
- Logic316
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The simple answer is that oil this much thicker when cold and thins out as it gets warm. My oil pressure pegs at idle when cold, then after it takes about 20 minutes to warm up and will drop down to about 3 bar (or half way).
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You have to watch out now... I used to own a 190E 1993 and got rid of it a year ago... My situation sounds very similar to yours..
I first changed my water pump as it went kaput, then head gasket, and then my idling speed keeps fluctuating so the mechanic got me to change the fuel regulator and after changing the regulartor, didn't fix the idling problem and hence my oil pressure kept going up and down while the engine is hot, but fine when start from cold... and then my cam shaft broke due to faulty install after head gasket fix (LONG STORY)...
After over $6000 of work over a period of 4 short months, I've decided to get rid of the lemon. Watch out.. it just seems like the same problem.
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