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Proud owner of an Blue-Black (Charcol Gray) '91 420SEL
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704 Posts
Discussion Starter #21
Well I am a very very poor owner.
I was 3 quarts low on oil.
Topped it of with Rotella 15W40 oul.
At idle and warm the oil pressure is pegged out per the factory cluster.
Have not been able to locate a gage to plug in to verify pressure.
 

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Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,528 Posts
Hey Jim,

Thats really GOOD news actually.

The orange/yellow light was due to a low oil level condition.. so we know that warning system works fine..

You've reported the oil pressure gauge works normally.. Thats just great!

While not an optimal series of events, I don't think any damage was done really.. as you know these V8s hold 8.5 Qts I think.. And the RED oil light never came on indicating pressure loss..

It probably needs an oil change, I'm guessing.. especially if its been a while, you know?

Thanks for connecting the dots here, Jim.

Stay Safe man.

M.
 

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Proud owner of an Blue-Black (Charcol Gray) '91 420SEL
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704 Posts
Discussion Starter #23
I have about 5,000 miles on the oil but this is the 2nd filter.
I normally do not run this many miles on oil and new oil and filter is being done this weekend if I can find that Wix filter locally.
 

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Premium Member
1991 560 SEL
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98 Posts
Glad that the main part of the mystery is solved!

And, FWIW, if you're still puzzled by overly high readings of oil pressure: sometimes the sender unit fails in a way that over estimates the pressure. I had my (likely original) sender fail and, in a moment of weakness, I bought one of the cheap replacements. (Very cheap.) It worked for a bit, but failed rather quickly and gave an overly high reading - 1.5 bar before even starting the car! So if you never find the oil pressure gauge to test with, and you're still concerned it's reading inaccurately, just replace the sender with a new - but not cheap - one.

Have fun!
Robert

Sent from my moto x4 using Tapatalk
 

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Proud owner of an Blue-Black (Charcol Gray) '91 420SEL
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704 Posts
Discussion Starter #25
I installed a $75 Bosch replacement unit. It did not change the pressure reading in the factory installed cluster.
I still need to find a wet gage to plumb into see what the actual reading is.
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,254 Posts
Why do you think it's wrong? The gauge should be pegged pretty much all the time, unless you're idling, at which time, the hotter the oil is the lower the reading will be. Cold oil will be close to if not at the peg, too.

There's really not much that could cause high idle oil pressure, save some catastrophes, like tight bearings.
 
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