Oil pressure gone to zero
 

1991 350SDL

Driving on the freeway, the oil pressure goes to zero. I coast off the next exit and park. There is oil on the dipstick. After a while there is a small puddle of oil under the engine, maybe a 1/4 cup total. No more is leaking. The car is home in the garage. I am not even going to look at it until tomorrow.

My thinking is that if there is no oil pressure, but the the sump is full, then the oil pump has failed. It is not the sending unit or the gauge, there is no oil pressure. The engine will start and run but it was just starting to get noisy due to no oil.

I have read that some vacuum pump failures can lead to this, but I an not sure if that problem applies to this engine. I will be checking the FSM for the oil pump R&R.

Has anyone else experienced and resolved this issue?

Thanks,
Greg

If you are sure that the sender and the gauge are working and that there is oil in the sump then the oil pump is certainly a suspect. I don't know whether your "rod bender" engine has a side oil pan like the OM603 in the W124 300D; if it does, you may be able to remove it after draining the oil and inspect the oil pump and its chain drive.

The oil pump R&R procedure requires removing the oil pan, of course, which requires lifting the engine a few inches with a hoist. This is an area which I have thankfully had no experience so we need input from others.

I opened the hood and looked around. I noticed that the "stop" lever on the IP is in the "on" position. When I push it down, there is a sound in the vacuum pump area, and the lever returns to the up position when I release it. The key is off and out.

Since no one who has had an oil pump failure has responded, I assume that an oil pump failure is rare.

As mention assuming neither the sender and guage have failed. Could be the oil pump chain has failed! You haven't mention any more leaked oil, a close inspection of the forward area of the oil pan might reveal a cracked or damage pan where the chain piled up.

A vacuum pump failure usually has the bearing coming apart with parts dropping down into the timing chain chase where a hard part gets between a chain and its sprocket. Maybe a ball bearing got between the oil pump drive chain and sprocket.

Running the engine at all is ill advised now, the cam will eat up the head in short order without pressurized oil. There are no replaceable bearings, only a rebore and new oversized cam if your lucky!

I had a 617 oil pump fail at about 350k miles. I pulled off a highway and the pressure dropped to zero. The pump chain was also in bad shape but hadn't failed. I do think oil pump failures are pretty rare.

This sounds like you have stored vacuum so the vacuum pump is probably OK. If you are concerned, the vacuum pump is a lot easier to pull than the oil pan; that would at least tell you what the problem isn't.

Greg, how do you know that the gauge and sender are OK? Not doubting you, just curious.

I was not conscious of anything wrong, but my subconsciousness was and instructed my eyes to look at the gauges. I saw the oil pressure gauge at 3 and then slowly drop to 0; it took about a second. The system was bleeding off the residual pressure. An electric gauge drops faster when it looses continuity.

That gauge had never acted erratically before.

After about 40 seconds the sound of the engine changed, consistent with the loss of oil pressure.

The sump was full of oil.

There was now a small oil leak that I still have not determined where it leaked from.

As soon as the gauge went down I put the transmission in neutral and coasted up the freeway exit. Stopped and then turned into a parking lot. The engine sound changed in the last 10 to 15 seconds, up until then I was hoping it was the gauge or sending unit. I have started to pull the pan and I hope to get it off tomorrow. I hope the problem is then obvious.

You may want to start looking around for another engine:(. It will be interesting to hear what the oil pump chain tensioner "slide" piece looks like.

My 1990 350SDL, Had a bad growling sound in the front of the motor, it turned out to be the oil pump gears were smooth ( NO TEETH ) some how I still had oil pressure.
So, anytime I change the timing chain, I check the chain and gears on the oil pump for wear, they are out of site and out of mine.
Good luck, I hope it turns out to be ok.
Jim

The pan is off
 

The oil pump gear was in the oil pan. The bolt had snapped off. The chain guide, that appears to have been cast into the block, was snapped off and in the bottom of the pan. It put a small hole in the front of the block that includes about 1/4" radius of the front main seal hole. This is where the oil leaked out. There was also a chain roller that was broken off the chain. There were also 2 small bolts in the bottom of the pan. I have not determined where they came from yet, but they may have caused the jam.

So, it looks like the engine has to come out to see if the block is repairable. I don't know how the chain guide could be replaced. I may post photos tomorrow.

I think I will be in the market for a 603.

Ouch! Sorry to hear of the fatality. OTOH, now we have an example of a rod-bender that didn't. Interesting that an oil pressure alarm would not have helped.

“The oil pump gear was in the oil pan.” Are you referring to the oil pump sprocket on which the oil pump chain rides? Or are you refereeing to one of the internal “gears” from inside the oil pump? Did the oil pump come apart or the chain drive which turns it?

“The chain guide, that appears to have been cast into the block, was snapped off and in the bottom of the pan. It put a small hole in the front of the block that includes about 1/4" radius of the front main seal hole. This is where the oil leaked out.”

I assume you are talking about the area directly behind the harmonic balancer? It sounds like the damage is actually to the timing case cover, which is where the front main seal is located not the engine’s block. That is a considerably less than catastrophic issue than a hole in the block. The single row oil pump chain has been destroyed? Or the double row cam/IP drive timing chain?

If you can figure out the size of the two bolts you found that would help figure out where they cam from.

You may simply need a new oil pump chain/sprocket/bolt/tensioner/spring and a timing case cover maybe an oil pump if that has been damaged.

I don't know that the engine will absolutely need to be pulled although you might want to eventually. You’d have to take the timing case cover off to get a look inside and see what might have actually happened. With the oil pan off, you would need to pull the pulley/balancer off the crank, then remove the two 8 mm allen head bolts at the front of the cylinder head's timing chain case opening, then you can with a razor blade seperate the head gasket and slide the timinig case cover off.

If you get to that point and decide to repair what you’ve got, I’ve got most of those parts from a 91 350SD 603.971 engine. Good luck!

Weak Point
 

On the "Newer" series diesels (601,602,603,606) is the Oil Pump Drive Gear
Sprocket and the Bolt that secures the Sprocket to the Oil Pump Shaft.

(I'm not EVEN gonna go on about a SINGLE roller chain!)

I've heard of other OM602s losing that bolt ["Backing Out"](Not breaking off ,yet)
AND I've got a Deceased 602 in the Garage that suffered the Bolt "Back Out" Syndrome.
('Nice People in Montvale told me I'm CRAZY to CLEAN and Loctite the Bolt on
the replacement engine...I put the GREEN Loctite on that sucker.)

There is a fellow here who has not posted lately who has several six o three engines which had bolts from, I believe it was the oil scraper, system fall off into the pan and work their way inside the metal screen over the oil pump pickup and lock the oil pump. Anything metal inside the oil pan, it would seem to me, could do this. Your chain part fits the bill.

If your motor did not lock up the bearings might still be servicable. I would pull whatever rod cap is availaable from under the car and look at the bearings before pulling the motor, assuming the other things you mention look repairable with the motor in the car.

You have a good ear to have caught the change in sound leading up to the loss of oil pressure.

Good luck!

Oil pump sprocket, not gear.

Yes, it is directly behind the harmonic balancer, it is probably in the timing case cover. I didn't even think about that area being the timing case cover. I was sad and tired, so I went to bed.

The small bolts probably are from the oil scraper, but I think that they were just sitting in the bottom of the pan and had nothing to do with this incident.

I still don't know what caused this yet.

The first photo is the parts found in the pan.
The second photo shows the hole in the cover.