Oil pressure: varying readings - PeachParts Mercedes-Benz Forum

mikeyfev1 · #1 11-01-2010, 11:53 PM

I just got home from a five mile drive in my 1985 300D KaliKar and I wanted to verify that the oil pressure readings that I see during operation are acceptable--I assume that the oil pressure is marked in bar units (0-3)...

Code:

 RPM    bar
===========
 800   1.75
1000   2.00
1300+  3.00

Does this look typical?

bustedbenz · #2 11-01-2010, 11:54 PM

Perfectly normal.

mikeyfev1 · #3 11-02-2010, 12:15 AM

OK, because I was watching YouTube videos of cold startup on W123s and I notice that they idle more slowly (mine is at 850 RPM; they seem to be in the 500-700 range) and even at slower RPMs they had oil pressure readings of 3. They all pegged the oil pressure needle even at idle.

Mark DiSilvestro · #4 11-02-2010, 12:42 AM

Quote:

Originally Posted by mikeyfev1

OK, because I was watching YouTube videos of cold startup on W123s and I notice that they idle more slowly (mine is at 850 RPM; they seem to be in the 500-700 range) and even at slower RPMs they had oil pressure readings of 3. They all pegged the oil pressure needle even at idle.

Yes. On a cold engine, oil-pressure readings will usually be much higher, often reading max at idle until the engine has been running for awhile.

Happy Motoring, Mark

bustedbenz · #5 11-02-2010, 01:15 AM

Quote:

Originally Posted by Mark DiSilvestro

Yes. On a cold engine, oil-pressure readings will usually be much higher, often reading max at idle until the engine has been running for awhile.

Happy Motoring, Mark

X2. Cold oil is thick and harder to pump. The pressure is significantly higher. When the oil gets hot and thin, the pressure is lower.

This can also be seen at the other end of the spectrum. If you drive at 60 mph up a 10% grade for 5-10 minutes, without overheating anything, then when you get to the top, that oil is absolutely toasty. If there's a stop light and you stop immediately after that climb, when every temperature is much higher than normal (but still safe) the oil pressure will sometimes drop down to 0.2 or 0.3 bar. Under these circumstances, the oil can get so hot and thin and the pressure can drop so that 1500 rpm is only making 2.5bar instead of 3+.

This is relatively normal. It's not "the best" for the engine... but it's simply what happens. All engines show it some, and all older engines show it a lot, no matter what. Just keep going and after 10 more minutes of cool-down time after that exertion, you'll be back to 3-bar pegged oil pressure above idle and 1.0-2.0 bar at idle.

vstech · #6 11-02-2010, 09:04 AM

your idle is high though. it should be in the 5-700 rpm range.