I'm looking at one 240D on Ebay and I noticed on one of the pictures the oil pressure gauge is pegged at 3 while idling with coolant temp at about 90C. In my car the gauge would be between 1 and 2 in this situation and I know that's fine. Is it possible to have so much oil pressure that it would hurt the engine? Or is this a case of a defective gauge? Or neither?

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

When I bought my SD, the oil pressure gage would be pegged anytime the key was on, weather the engine was running or not, weather idling, or cruising the freeway. I found out that the wire to the sending unit was off. Hooked it back up, and it works fine now.
Not sure that a 240D would be the same, but just an idea.
Oh, yes. It will also be pegged now when the engine is cold and idling. As the engine temp goes up, the idle pressure goes down. But my engine is pretty fresh still.

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past MB rides:
'68 220D
'68 220D(another one)
'67 230
'84 SD
Current rides:
'06 Lexus RX330
'93 Ford F-250
'96 Corvette
'99 Polaris 700 RMK sled
2011 Polaris Assault
'86 Yamaha TT350(good 'ol thumper)

FWIW my 240D with 145K miles reads 2.5 bar at idle with the oil fully heated up (like after running for an hour). I haven't paid attention but its possible that it reads 3 bar at 90 degrees coolant temp before the oil is completely heated.

Rick

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80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

240D's also have a manual idle adjustment knob on the dash and many owners are not familiar with its purpose. When cold they like to have the idle speed increased, and then when warm it can be lowered. If the owner just leaves it high you will likely see the oil pressure gage pegged at 3 atmospheres as the "idle speed" is not truly set at the correct rpm value. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

That's not necessarily an indication of an engine problem. That could simply mean that the O-rings on the oil filter cannister lid (the ones on the rod that sticks down in the filter) are bad, which is a common problem. My oil pressure gauge fluttered at times before I replaced the O-rings; now the gauge's smooth as silk.

Thanks guys for the replies. I too suspect it's the idle adjust knob. By the way, here's the image. Can someone tell me what setting the knob is at?

Attached Thumbnails

 

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I don't think you can tell what setting the knob's at by looking at it; I think that it's made to make many revolutions to do what you need, as opposed to only turning 90° or 180° or whatnot.

I would say play with the knob until it sounds about like your 300D does, and see where the needle is then. If the needle's still pegged, it might be worthwhile to get one of those cheap-o mechanical oil pressure gauges from Kragen just to verify what the dash gauge's reading (there's a remote possibility that the internals on the dash gauve could be bad). If it's still reading high, I wouldn't seriously worry about it...better to be high than low, as long as it isn't too horribly high. Even still, as was mentioned, if the oil pressure's really that high at low idle at that coolant temp, it's probably a bypass or whatnot...

Good luck!

DDH, I like that idea...in fact, I still need to replace the O-ring that's on the dipstick. The ones that were on the stem were hard as rocks! I had to break them (depressingly easy to do) to get them off...

My '72 is always pegged. Hot at idle, during the summer, in the sun...ect. My gauge works properly, as it takes a moment to rise on start-up, but it is always pegged. My $0.02.

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1992 500SEL 25K
1995 E320 40K
1995 SL600 120K
2002 JX8 Sport 43K
2005 Volvo S40 95K
2006 Isuzu NPR 304K (Frankencamper)
2007 Crown Victoria 150K
2014 Smart Electric 20K

Ditto Antony. daBenz came off the peg once, when I lugged up a big hill and was watching the scenery instead of the gauges. Caught it when coolant at 200F, downshifted and ran 45mph, coolant went down and oil pressure pegged again.

I think you'd have to temporarily install another "good" pressure gauge and block off part of the radiator to get things good and hot in the garage, if you really want to test things. 220D/240Ds have big radiators.

To adjust the knob: you want no effect for the first quarter turn or so. After that you get what you get when you turn it up. Set the low idle first per your engine, then set the fast idle knob at the engine side of the cable. I loosen the cable, turn the knob 1/4 turn, then set the cable, all with the engine off. Sometimes takes a couple of tries. Turning down the idle before driving is the correct habit to get into, in my opinion.

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daBenz - 1970 220D