Loss of oil pressure at high revs

[Uberwagon]

Hi all,

My poor 500E is not having fun at the minute. A few car park dings by idiots and now a mechanical headache, just as I was going to give it some money and TLC.

During normal operation in the UK I have 2.0 bar oil pressure at idle, 3 bar as soon as the revs rise and when very hot it only drops to 1.5 bar in drive. So all happy numbers. The engine sounds smooth and is regularly serviced, it's always felt strong and pulls hard in all gears.

5000rpm noticed the oil level fluctuating in quick bursts, down from 3 bar to 2, still flickering and then flickering to 1 bar. I backed off right away and the oil pressure came back to normal, 3 bar on the gauge.

If I hold it in 1st gear and slowly go to 6000rpm I get no oil pressure flickering, only when under high load when accelerating.

I changed the oil and filter and the same thing happened. I have heard of the pickup becoming blocked with debris from broken rails and also of a faulty oil pressure sender. I will fit a new sender first once I get back from work in a few weeks and will order the parts to do the upper chain rails and possibly the chain aswell, for preventative maintenance.

It has done 150,000 miles and is an early 1991 model. I only use genuine parts, filters etc and the engine was fully up to temperature when this happened.

Anyone have experience of this? I will be putting a mechanical gauge on it somewhere to be sure.

I will also drop the sump and fit the newer type strainer cap.

Dave!

 

[gsxr]

Most likely this is caused by either a failing sender, OR the lower wiring harness. If the lower harness is original, replace it on principle, or at least order the harness while it's still available...

 

[Uberwagon]

I'll get a price on the lower wiring harness too. It certainly gives you a fright seeing the oil pressure drop at such high revs and load.

Dave!

 

[samiam44]

I'd think you would hear chain rattling if your rails were broken in the sump. Definitely a maintenance item to clean the lower pump- replace the screen grommet/screen with the larger updated one, new gasket. You are in there- replace the orings on the oil level sensor or replace it.

The sensor is attached to a little metal pipe which attaches to the oil filter housing. Buy new crush washers.

M

 

[Uberwagon]

I only get a light rattle on a first start up as I work 4 weeks on, 4 weeks off. I didn't think a broken chain guide gave any symptoms though unless the main guide lower down on the front was broken. I thought the first signs were when pieces of it were found in the sump?

I'll do the oil level sensor O-rings while I'm in there. I really hope it's just a spurious signal under load as it would have to sit and wait for a few years if it was anything more serious.

Dave!

 

[jhodg5ck]

I've seen some 119's w/ very broken guides and a fairly clogged screen, still no starvation visible on the oil pressure gauge..plus, these all have aluminum main bearings, they don't tolerate a lack of oil for but a few seconds..!

When you drop the pan, I would go ahead and order a new [oil level] sensor, they're cheap and the old ones are typically crusty/wiring starts to degrade w/ a lot of age..that and they don't always like being Touched, so put it all back together and Poof, back in again. I would also recommend a high Quality sealant on the oring to the oil level sender. 99.9% of all M119's start leaking there before anything else.
New orings work for a minute but they invariably Fail before any other of the seals down there.


jono

 

[Uberwagon]

A little update on this....

I removed the lower sump pan and the crankcase looked excellent, nothing at all in the sump pan, 3 small bits of debris probably from when filling with oil and very little lawyering inside the engine.

The pistons I could see had some fine vertical scratches but nothing worth worrying about after 150,000 miles.

I replaced the strainer, fitted the newer type suction rubber, new pressure sensor and level switch.

My lower wiring harness is kaput, lots of cracking, bad insulation etc. I've ordered a new one in the UK but they get made to order now, 1 at a time. It's $400 including tax.

Oil pressure on a hot engine after a run is 1.8 bar, no pressure fluctuations at high load and high revs in every gear, so mechanically it is fine.

I will replace the upper wiring harness and go through every hose and connector I disturb along the way during the winter hopefully.

very happy with the outcome, it could have been expensive.

Accessing the lower pan bolts with the oil cooler lines in place is a real pain, you have to disconnect the pipe and fit a new cooler o-ring to remove all the bolts but the spacer brackets for the pipes still make this very awkward.

Many thanks for the part numbers and advice from this forum!

Dave!

 

[alabbasi]

Check the oil level at the dipstick. Being actually low on oil will also cause this..... NVM, I just read post #7

 

[jhodg5ck]

$400 to fab a harness? I need to charge more..

 

[gsxr]

$400 to fab a harness? I need to charge more..

That's a 500E harness, which is still available new in USA for $310 list, $230 Naperville. Not worth rebuilding these yet, IMO...
http://www.mboemparts.com/oe-mercedes-benz/1245402730

It's the .034 / 400E420 harness that is NLA and I'm sure some folks would pay $400 for a fresh one!

 

[jhodg5ck]

I've built both, but yes...doing a decent number of 034 harnesses.

Debating if I feel like building the upper harness for the SL700...it's available but it's some coin.

That said, if someone needs a harness built or Re-built...ping me out. We've got all the stuffs to do it Right/Right!

jono