300D no oil pressure!

[Dusty-NZ]

Help ! my wayward '82 300D surprised me this morning , by displaying no oil pressure when started up . I checked the oil level (the sump is full) and restarted it , reved it gently to about 2000rpm and the needle of the oil pressure gauge just came off the bottom stop.
There appear to be no odd noises , as much as one can tell in a cold diesel , but I have no idea what to look for ,, we need the car for every day transport ,,
All thoughts on this problem gratefully recieved.

The car has done 350,000 and was working perfectly (I thought) .
Ihave thought about changing the oil and filter , but this has never shown any changes in performance before ,, thats all I can think of,, I hope it is not past it's useby date , we have really enjoyed this car .

I know on cold days my oil pressure needle sometimes sticks to the peg and I have to give the cluster a tap for the needle to break free and register..

But since yours is moving slightly, this does not look like the case. I would check to see if the guage is infact working, then I would start looking for a new oil pump.. Just don't drive the car until the problem is resolved.. you will ruin the engine.

[P.E.Haiges]

Dusty,

I would check the oil pressure with a gage that you know is good.

Run the engine as little as possible to do this.

If the good gage reads also no oil pressure I would start by checking for any oil leaks in any of the external oil lines. Probably a leak bad enough to cause the no oil pressure problem would dump a lot of oil on the ground. If no leaks are found, check the oil pump. It isn't likely to be the oil filter, they are designed to pypass if they get plugged.

Whatever you do, don't drive the car before you have oil pressure. If it has to go to a garage, tow it there. Running without without oil can damage the engine bearings and rings in a hurry. A complete overhaul or rebuilt engine would then be required:$$$$$$$$$$$$$$$$$$$$.

P E H

[P'bert]

I had a similar experience with a 240D I owned until recently. The cause was a small bit of debris caught in the oil pressure relief valve, debris from a vacuum pump which was gradually disintegrating. The oil pressure relief valve is incorporated into the oil pump, which is easily accessed by removing the smaller of the two oil pans.

Phil

[jassz]

We had a Buick once that seemed to have a very sensitive oil pressure guage. If I ever went too long between oil changes, it would start to bottom out. I was told it was likely due to grundge making the guage stick (there's a hi tech term for you! :p )

[Dusty-NZ]

Well , I checked the oil gauge and its ok ,, I guess the pump needs inspecting ,, I shall try and get into that this w/end .
P'bert , please tell me more about the vaccuum pump thingy ,, perhaps thats why my central locking has gone a.w.o.l.
Many thanks for all your helpfull suggestions .

[P'bert]

The incident I was referring to involved my '79 240D, which had the old style vacuum pump.

My first indication of trouble was the loss of oil pressure at idle, though the pressure was ok at higher rpm's. Investigation of the oil pump revealed about a dozen 1/8" ball bearings in the strainer, along with several smaller pieces of metal. Further investigation found some more of the smaller bits in the oil pressure relief valve. Once all the debris was cleared away, the oil pressure was fine, and I certainly was curious where the debris might have come from. Mind you, during all of this, the vacuum was quite ok.

A month or two later, I was driving home from the city when...what do you know, no vacuum boost for the brakes. No engine shut off, either. And no vacuum anywhere. Well, the vacuum pump had failed entirely, probably leaving some more debris in the oil pan, and most definitely leaving me with no vacuum system. That it had continued to work for so long, with its thrust bearing (probably not its real name) half destroyed, is quite amazing indeed. A "new" pump from the wrecking yard solved this problem.

I don't recall which year your diesel was made, so I don't know which vacuum pump you have, but if you've experienced a total loss of vacuum coincident with a loss of oil pressure, then I guess you know what's up.

At any rate: (1) don't drive it; (2) remove the oil pump; (3) clean the screen and the relief valve. None of this is very difficult, especially if you have means of getting your car up into the air.

Phil

[Dusty-NZ]

OK , OK ,, you've convinced me ,, I'll push it from the car port into the shed .
Thanks Phil ,, I will get into it very soon , it's good to know what to look for ,, never been into a merc before ,, just the old Chevy ,,, but they are all just mechanical contrivances (designed to keep us poor and off the road) LOL . .
Man I hate that black diesel engine oil , seems to get every where but a blokes gotta do what a blokes gotta do .

These engines use a chain driven oil pump. It is possible with a sudden loss of oil pressure that the small chain broke.
If you can't find the problem where Phil has said then be sure to look at that small chain. It can be hard to sort out what you are seeing in there, but with the small oil pan off it should be visible.

[airfoill]

Originally posted by Old Deis
These engines use a chain driven oil pump. It is possible with a sudden loss of oil pressure that the small chain broke.
If you can't find the problem where Phil has said then be sure to look at that small chain. It can be hard to sort out what you are seeing in there, but with the small oil pan off it should be visible.

If memory serves, I believe that these engines use a gear driven shaft layout; there should be no oil pump chain. The chains came into the scene with the newer series engines (i.e. 60X and beyond).

Herb
'82 240D
'87 300SDL
'92 300D 2.5 Turbo

[P.E.Haiges]

Airfoil,

The 616 series engines have a chain driven (off the crankshaft) oil pump. Older engines were driven off a shaft that was connected to the injection pump drive. I had that shaft break once and ruined a 190D engine. The gasoline engines had the distributor connected the same place.

P E H

[Dusty-NZ]

Well , I finally got time to get under the car and check this thing out .
I took the front sump off and removed the oil pump, the sump was very clean inside and the pump has no faults , I tried the shaft drive with the 15" screw driver and it seems very secure .
Fitted it all back up , took the plug out of the block ( where the dist would go ) and checked that the pump drive shaft was turning ( it was ) , fitted a new filter and O rings on the filter housing shaft , started it up again ,, yep ,, still no pressure
At about 2000 rpm it holds pressure on the gauge , but below that , nothing is indicated ........
Any thoughts on where I go into it next ??

[kerry]

This may be grasping at straws. On my sailboat engine, there is a plug in one of the oil galleries. If someone leaves that plug out on a rebuild, the engine cannot build oil pressure. Is is possible something like that is occuring in your engine. If there was a leak somewhere, it might explain how pressure can build when the RPM is high. If there is no evidence of an external leak, perhaps someone knows if there is an internal leak that would allow oil to go back into the sump but not build pressure.

All that being said, the typical explanation of circumstances similar to yours is worn main and rod bearings. But the sudden occurence of the event seems inconsistent with this explanation.

Use latex gloves to keep the oil off your hands.

[BIGRED]

From my CD manual it says

"On engine 6125, the pressure relief valve is screwed in or on, respectivley, main oil duct at engine face and on engines 616/617 at oil pump."

"If the is no oil pressure or if the pressure is too low, check whether oil pressure relief valve on oil pump has dropped or become loose. In both cases, coat threads of oil pressure relief vavle with sealing compound, part No. 02 989 94 71 and screw in."

Good luck
Don

[Dusty-NZ]

Hmmm , , well the engine was running just fine , so ,,,,,,,, .
I looked at the relief valve on the pump and it was very tight so I didn't even try to remove it ,, perhaps I should have ,, could the spring have failed ?/