here's a question...

my oil gauge is measured in lbs. per quare inch from 45 (at the top) to 0 (at the bottom). when i'm in idle or stopped, the gauge rests at the top line (45lbs) but as soon as i start driving, it slowly shifts downward and rests just around 30 lbs (the second line). when i took the car in for an oil change and filter change [thanks MB Motors!], it was hanging around 40 -45 for about a week and then is shifted to around 30. does this signify a loss of oil or is this standard? why does it shoot up to the top line (45) when i'm in idle or at a stop sign?

also... i've yet to take the car out on a long freeway drive (longer than 25 minutes) but i'm feeling the transmission thump when it shifts up. granted, i've been doing mostly street driving but the transmission fluid levels are fine. what does anyone out there think may be causing this gentler thump into a higher gear? anyone think it's time to try a TRANS-X deal? or the "italian tune-up" i hear about alot on these boards? or is this something to be expected with stop and start L.A. traffic?

thanks

All my gauges are in metric bar. The typical range is 1.5 bar at idle rising immediately to the "peg" of 3 bar at anything above fast idle. Hopefully someone who has gauges in psi can tell you what the nominal is for yours. Is your oil level correct- between the min and max marks on the stick?

The transmission, if it otherwise shifts normally, sounds like needs a modulator adjustment. MBZ automatics tend to shift a little harder than American cars. Check the archives and you will get tons of info.

An Italian tuneup won't help your transmission, but will blow the carbon out of your engine.

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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 (??)

Chetbaker,

Not sure about your transmission issue, but I think vacuum is used to control shifting, and it is possible you may have some leaks. Do a search on the subject as much has been written in the past.

The oil pressure issue is peculiar. Sounds more like the pressure gage is failing as higher rpm should mean higher oil pressure. The pump is a "positive displacement pump" and as the rpm speeds up the pump speeds up. This means the pumped volume increases linearly with engine speed. The flow resistance forces the pressure to rise. There is a relief valve in the oil circuit, and it is feasible that this valve is off kilter, openning too soon (too low a pressure) and then hanging open until your flow rate drops at idle. In either case, this would drive me nuts and I would have to fix it as low oil pressure under load is a death sentence for your engine.

Hope this helps. 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)

Chet,

The oil pressure problem you have is very unusual.

You might connect another oil pressure gage to see if it reads the same your dash gage. If they read the same, I would look at the relief valve as being the culprit.

P E H