Hi everybody, long time no post.

My question is regarding oil pressure readings at idle with Mobile 1 5W-40. I helped a friend change his oil and filter on his '82 SD, and on his way home he was a bit alarmed at the low pressure readings when his foot is off the accelerator. I assured him that a little fluctuation is normal, but he said the readings were near the bottom. I don't remember seeing readings that low on any of my diesels, should we be worried?


Thanks

__________________

At idle its normal for the pressure to drop to about 1 bar(15 PSI), but must rise to 3 bars(45 PSI) at about 1300 RPM.

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg

Got it!

__________________

Did you guys change the 2 little O-rings at the bottom of the Oil Filter Stem?

Also, what RPMs is the idle set at?

__________________
84 300D, 82 Volvo 244Gl Diesel

No we didn't. I noticed they were pretty flat, but they didn't come with the filter so we were stuck leaving them on. You think it has something to do with the low pressure?

I'll ask him about the idle rpms.

Thanks

__________________

Replacing those 2 O-rings (size 6x10x2mm) has cured the low idle Oil pressure for some members but not all. If Oil goes by those O-rings it goes back into the Oil pan.
Also iside of that long stem itself is a Check Valve. If you have access to compressed air and an Air Gun at the top of the stem there is a little hole. Blow compressed air through that little hole in a short burst to clear anything that might be trapped under the Check Valve and keeping it from closing (one member said he pulled cotton that had come out of the filter from the Check Valve).


In the above picture a small amout of Oil passes through the upper portion of the Oil Filter (the bypass section of the oil filter) and goes into the small hole at the top of the Oil Filter Stem.
The Oil travels down the stem and goes past #19 the Check Valve.
After going through the Check Valve the Oil continues down the stem past #20 and #21 (these are the 2 O-rings, when you order them you get 2 that are the same size).
The Oil goes out of the stem into passage C and back into the Oil pan.

Another thing I forgot to ask is if the oil he had in the car before had a higher viscosity?
Meaning that if the old Oil was thicker it could have a higher idle pressure than the new thinner Oil.
Also, if it is still there; there should be a tag up near the Radiator that has the proper Idle Speed for your year and Model written on it.

__________________
84 300D, 82 Volvo 244Gl Diesel

Thanks for the great info Diesel911. I'll definitely be getting the o-rings and add clearing the stem to my oil change routine.

We have no idea what the last mechanic put in his car.

__________________

The Oil change Lube-and-Tune type places sometimes put a little sticker on the door frame of the car saying when the Oil was changed and what Oil they used.

You need to remind your Friend that no matter who does the Oil Change he needs to know what Oil and was put into his car in case he needs to add a little later.

__________________
84 300D, 82 Volvo 244Gl Diesel

Although I usually put Chevron Delo-400 15W-40 in my '85 300D (W123, OM617), I have used Mobil-1 5W-40 and I don't recall any significant difference in oil pressure at hot idle. The factory says anything over 0.5 bar is OK at idle but the pressure must climb to 3 bar at engine speeds above 1300 RPM--as was said in an earlier post.

Definitely change those little o-rings and make sure the inside of the pipe isn't clogged. You can also squirt Brakleen or whatever cleaning solvent you use into the pipe. Because the exit hole is so tiny, you have to give it time. I rigged up an adapter for my air compressor that allows me to attach a piece of heavy plastic tubing to the end of the pipe. With the air pressure set to about 5 psi I can go away and let the old oil and crud gradually ooze out of the little hole until nothing comes through but air.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Someone mentioned the "O" ring closest to the cap is a 7x11x2, I believe 'em, yet have been using 6x10x2's. If you find any 7's, let me know.

Attached Thumbnails

 

__________________
83 SD

84 CD

This O-ring kit I bought at Autozone for about $8 below has 24 of the 6x10x2 O-rings (the size you get if you order the O-rings for the stems) and 24 of the 7x11x2 O-rings. Dorman Value Pack Metric O-rings part #799-450

Attached Thumbnails

 

__________________
84 300D, 82 Volvo 244Gl Diesel

Thanks.

__________________
83 SD

84 CD