616.916 Oil Pressure Too High

[gmog220d]

Car is my '74 240D with 616.916. Ever since I bought the car I've noticed that the oil pressure gauge never drops from max pressure, ever. I can run it balls out on the freeway and get off and at idle the needle will still be pegged. The only way I've seen it come down from max is by adjusting the idle way low.

Today I removed the instrument cluster and installed another stock gauge from an extra cluster and just let it hang out in the dash opening while driving around the neighborhood and got the same results, so it's not the gauge. I don't believe there's a blockage in the lubrication system - engine runs and sounds great and temp stays normal under all driving conditions, and it hasn't seized up or started making "bad" noises in the few thousand miles we've put on it.

I've studied up on the oil/lubrication system and my thoughts go towards the pressure relief valve that's in the oil pump assembly. Could it be stuck closed, not allowing the pressure to bleed off like it's supposed to?

Problem in the filter top? Doesn't seem likely as I can't see how a problem with the oil cooler bypass or overflow valves would cause high pressure.

I have changed the oil and fine filter canister a few times and both filters, including the main strainer screen, are installed correctly. I run Rotella T 15W-40, same as I've used in other Benz diesels and have never seen this problem. I searched the forums and found no matches.

Anybody else ever experienced this?

[greazzer]

My 1982 240D 616.912 did the same exact thing. I have a thread on it if you wish to look at it. One day it stopped being pegged at 3 BAR max. I think because my current car was stored forever, it somehow got plugged up or there was goo in the line, or who knows. Now, I don't drive the car a bunch because of CC insurance, but when I do take it out for a spin, it will drop to around 2+. The pan was dropped and the oil was like Hershey syrup. It's still pretty Hershey syrup like under the valve cover (cam cover) so I am guessing the oil will take a number of changes to flush it out.

[gmog220d]

Link for the lazy to that thread?

I bought this car 3 - 4 years ago, and it had been sitting around for about 5 years at that point. I bet it sat around in a garage before the kid I bought it from picked it up, too. Odometer is at about 99,000, and think there's a decent chance that mileage is for real. No rust, pretty decent original paint, original windshield, pedal pads are not worn that much, etc.

But the inside of the engine is clean, clean, clean. No signs of any mucky build-up. I've had the lower pan off before and it was clean enough to lick. The car was maintained well before I got it. But I too have had thoughts about some muck sticking the pressure relief valve up.

So far, since purchase, I've put less than 10,000 miles on it, most of that around town. The longest trip it's done was the 600 miles between New Mexico and Utah. Maybe the relief valve would free up with some more driving. I think I'm going to pull the lower pan off and check it out anyway. I know from VW experience that high oil pressure is a power robber, oil heater, and can cause the oil pump to wear faster.

[greazzer]

Motor Oil Question ? W123 240D

[gmog220d]

Thanks for the link.

I may hold off on pulling the pan and try the Marvel Mystery Oil trick.

[barry12345]

Since it does drop down with a hot lower idle and if the engine only has 99k it possibly is normal? Perhaps you normal idle is a little higher than spec?

As soon as I give mine just a little more fuel and I mean only slightly more they all peg even on very hot days after very long highway runs.

The worse never drops to less than a two during really hot idle. This is on 15-40 dino oils.

I always gave Mercedes full marks on their lubrication systems in providing more than adequate lubrication in their engines going way back.

I guess if this really bothers you hooking up an external gauge would be required. On a cold engine you probably should not see much above 60-80 pounds pressure if that relief valve is normal.

[greazzer]

I would be careful using any flush or even something which might thin out the oil. Not sure how the bearings would like that. My plan is to drive it 500 miles, then change the oil again, except I need to change out the front crank seal, so I am waiting to do that. Mine was not driven a ton before the 3 BAR peg reading went away, but it did worry me since my prior MBs would peg at 3 BAR at start-up but went away after warming up. They never went below 1.5 BAR. Right now, mine never goes below 2.5 or 2.225.

[gmog220d]

RE: Idle speed. I don't have the tach attachment that's driven off the oil pump/intermediate shaft drive, so I am guessing when it comes to setting idle. It's been a while since I tried lowering idle to the point I saw pressure drop on the gauge, though, and that could have been during winter. Perhaps idle is a little on the high side. I'll lower it a bit and check out that possibility.

Thanks for the responses!

[86-300sdl]

Different Motor...Same Experience...

My SDL with now 432,+ miles went to 3bar at idle after an oil and filter change some 15,000 miles ago. Always had been around 2bar at idle then 3bar with a touch of throttle.

Worried as you are I pulled the Pep Boys Purolator (which I had used often when Mans filters weren't readily available) and replaced with a filter from the dealer ($14).

Oil pressure back to normal.

So I'm not sure we are talking apples to apples but for a few bucks you can rule out filter restriction of some sort.

I change oil every 3k and so I have about five changes since the high pressure scare. Every time I've just got a MB Dealer filter and things have stayed fine.

[gmog220d]

Right on. Barry, you nailed it. I romped the car down to the Slow Reilley's to take some old oil for recycling - got it good and hot. When I got home I dropped the idle a half turn of the screw and the pressure needle just drops down from max now. Sweet. Looks like it was a little on the high side, and may still be.

I've always used Mann filters from Pelican, or ones I've gotten from the dealer (Mann as well). I too change every 3K or so. Just changed it today with about 1000 on the clock since the last change, a year ago this July. Thanks for sharing your experience 86-300sdl.

Incidentally, the gauge in my W115 is in PSI, and it maxes out at 45. 45 PSI = 3.10264 bar. Looking at the specs on pressure relief valves, there's either an 8 or 5 bar valve in the engine, most likely the 8 bar. So the pressure relief valve would not be a factor even with the needle up at 45 PSI.

Sorry for posting a non-issue! And thanks again for all the replies.

[barry12345]

Originally Posted by gmog220d

Right on. Barry, you nailed it. I romped the car down to the Slow Reilley's to take some old oil for recycling - got it good and hot. When I got home I dropped the idle a half turn of the screw and the pressure needle just drops down from max now. Sweet. Looks like it was a little on the high side, and may still be.

I've always used Mann filters from Pelican, or ones I've gotten from the dealer (Mann as well). I too change every 3K or so. Just changed it today with about 1000 on the clock since the last change, a year ago this July. Thanks for sharing your experience 86-300sdl.

Incidentally, the gauge in my W115 is in PSI, and it maxes out at 45. 45 PSI = 3.10264 bar. Looking at the specs on pressure relief valves, there's either an 8 or 5 bar valve in the engine, most likely the 8 bar. So the pressure relief valve would not be a factor even with the needle up at 45 PSI.

Sorry for posting a non-issue! And thanks again for all the replies.

Yes the oil pressure gauge does max out. I suspect the designers decided this was just better than having one fluctuate at the higher values. Your model at low total milage is getting quite rare now.

[gmog220d]

Originally Posted by barry12345

Your model at low total milage is getting quite rare now.

Agreed. I've seen photos of some pretty nice W115s, but this '74 is the nicest I've seen in person. Far from "perfect", but still quite nice for a '74. I got lucky finding it on Craigslist back in Albuquerque. Bought it from the third owner for a song, a young guy who spent a lot of dough on it at one of ABQ's costliest shops and then parked it in his garage. He bought it from the estate of the fellow who bought the car from the original owner back in '75. I got a stack of paperwork with it including the original invoice with all options listed. I have all the original keys. Also got service records up to a few years before I bought it (hence my belief that the mileage is accurate).

Thanks again for your input!

[atmacg]

I have just checked my instrument panel oil pressure gauge OM617 1981 NA against the gauge on my air compressor (using air pressure) and a kit gauge for adjusting fuel pressure in CIS systems. The MB gauge always read higher by about 30%, than the compressor and kit gauges which were very close.
The MB oil pressure gauge behaves in accordance with other posts, pegging at 3 bar indicated when driving and dropping to about 1 - 1.5 bar on hot idle. I presume that MB have deliberately miscalibrated the oil pressure gauge in this way.
It is interesting to note that all three of the w123s I have owned have given a speedo reading 10% greater than actual, presumably to save the owners from speeding fines.