Am still puzzling over this -- suddenly oil pressure went from 25@hot idle to 5-8@hot idle, and pegged (45) only at high revs -- town running shows about 30lb. I have not checked the gauge against another one because I do not have a spare & am not anxious to spend $20 for a gauge I'll use once for 1 minute as $$ is very tight. The dash gauge, however, acts like it's functioning normally.

I talked to a man with a lot of varied (but not MB) mechanical experience who suggested that my symptoms sound like a check or bypass valve stuck open. This seems to correlate precisely with what I'm seeing on the gauge -- that pressure takes longer to build up at all than it used to (seems like the filter housing is empty every time I start, like after an oil change), and falls much faster when the fuel pedal is released than it used to. And, lower total pressure would be explained by the pump's inability to build higher pressure with the valve stuck open.

The pressure relief valves and check valves seem to be both built in to the filter housing. Has anybody ever played with these .... or should I just try a used housing? (anybody have a spare housing around for sale?)

Any knocking or pinging? Gauge should be pegged by 1500RPM, mine is at 1200.

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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

Have you replaced the two oil filter stem O-rings recently?

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"spreading a trail of obnoxious where ever we go"
1981 300sd w/ 341,500 miles

http://www.wecrash.com/pics/ddda_banner.gif

No, the engine sounds a bit rattly at idle - like it used to at start until the needle pegged - but sounds fine at higher revs. 240s don't have a tach, but mine used to (until 2 weeks ago) peg quickly... now I can run 55 in 5th & it shows 30lb.

I pulled the filter apart when the problem occurred to check if I had left the old O-ring in there, and noted that both centershaft O-rings look OK. They are a year old or less.

Did your gauge ever peg out at 55 in 5th? or is this 30lbs new?

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Also check for oil seepage behind the instrument cluster. Common prob with later version OP guage is they crack at the coil. Seen this on coupla '83/84 MB diesels. It's an insidious problem too, typically folks dont realize the guage coil cracked and spittin oil until the carpet gets soaked.

240D with a 5 speed manual, those are very rare.

__________________
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

Stevo,

Before this recent change, mine never went below 25, and would peg immediately as I came off idle. Now I can be cruising & see 30 lbs. I have noticed no drips from behind, but I'll check tomorrow.

The car was originally sold in France, to the wife of the man who got shot out of the cannon for the circus ... they moved to Venice (Fla) like many other circus folk.

Sounds like the guy you talked to is on the right trail. If you don't have a big leak or high consumption then there is something blocking the oil flow or leaking back the the sump before the filter.

Pull the valve cover and be sure the oil rail is spraying on the cam lobes and not cracked/broken. If that is good then its time to drop the lower oil pan and have a look at the pump, relief valve and shaft bushings.

Sounds like your car has a colorful past

The oil pump is easy to pull if it comes to that. theres just a couple of steel impellers and bushings that can ware. It would be nice if you could swap one in and see if theres any change.

__________________


1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Aren't the relief valve and the bypass valve both built in to the bottom of the filter housing? Mine doesn't have an oil cooler, so there are no outlets for that ... otherwise it looked like late (83-85?) filter housings for 616-617 are the same. Has anybody ever fiddled with these? I'll definitely check the rail in the valve train. I also think I'll tap the filter housing with a rubber hammer & see if the relief valve will unstick.

I don't mind replacing the oil pump ...... but it doesn't seem logical that it pumped fine one day, and much lower the next. It seems more likely that some restriction that used to help build and hold pressure isn't doing so any more.

Estod, it aint unheard for oil pump screen to git trashed with grit. Also seen screens punctured with nut's bolts and whatnot in the sump gettin sucked into oil pumps gears Pulling the sump aint bad idea, specially if its high mileage engine. Then just cleaning the crap will make it worthwhile chore.

Otherwise worst case scenario nobody's mentioned yet - spun rod bearing For this i been told one diagnostic method is check the oil filter for metal shavings using magnetic probe. Heck use the same metal shavings search method prowling the sump to help eliminate this worst case scenario.