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I have an 89 Mercedes 300 SE and recently the oil pressure needle has been stuck at the highest point when I accelerate. The values on the gauge are 0 to 3. When I take my foot off the gas the value goes down to 2 or less.

There was some knocking shaking sound this morning but after I turned the volume way up on the radio I couldn't hear it any more (bad joke). Also, if I let it idle for a minute or two it seemed to go away, no knocking or much less.

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  • Do you change your oil and filter often? Maybe restrictions or sludge in the valvetrain or a gummed up filter?
    – Mike Saull
    May 1, 2013 at 2:57

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Assuming that the Engine Oil Level is OK then you're gauge readings should resemble the following.

At idle, the gauge should be between 1.5 and 3 depending on how long the vehicle has been sitting and the temperature outside (there are some other things that factor in here. Just trying to not complicate things too much.)

Accelerating / Driving, the gauge, for the most part, should always peg at 3.

The gauge reading you're asking about seem to be correct. The knocking you're hearing is probably due to either using the incorrect oil weight (you should be using a 20-50 oil in that straight-6 or something like it. Also, Please double / tripple check to ensure that oil level is correct. And if needed, get your oil changed by a trustworthy mechanic.

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  • My Acura manual states a minimum grade gasoline and going below will cause engine damage and knocking. Could that also be a possibility here to explain the knocking?
    – Andy
    May 4, 2013 at 19:35
  • Yes. The "will cause engine damage" is a bit extreme. But, it will without a doubt knock and eluminate the Check Engine Light.
    – cinelli
    May 29, 2013 at 8:47

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