W124 M104 Oil Pressure - Where has it gone?

[SNST]

My 95 TE280 sounds very happy. The oil pressure gauge suggests it shouldn't be! Problem has started in last week.

When hot, the pressure at 600rpm showed zero a few days ago. Now goes to zero at less than 1000rpm on idle, but not under power, so obviously the problem is getting worse. I have left it idling for several minutes, listening VERY carefully, but no untoward noises either at idle or under load.

Cam lobes have good oil cover & throw off some drips at idle, much more on increase in revs, so the oil seems to be there in at least adequate quantity.

I know I have an oil leak near the filter housing, but can't see where without significant dissassembly, so I've ignored it for a long time.

Does anyone know how long the engine will put up with ACTUAL zero pressure at idle before noise/damage shows up? Has it already shown that it must be the sender or gauge?

How easy is it to fit a pressure gauge? Is it realistic to fit a tapping to the top of the filter cover?

I'm trying to prove it is the sender, prior to 200 mile trip I have to make tomorrow.

PS Oil is clean & 1st thing I did was fit new MB filter.
204000m on the clock

Any advice & experiences welcome! I will keep board up to date on results

 

[television]

The chances are the sender has failed and usually just screwed into the oil filter housing, I had one doing the same, OK when cold but when hot it was all over the place, you can screw a gauge into the hole where the sensor sits to take an accurate reading.

 

[SNST]

Thanks. I would like to confirm the pressure is OK before shelling out about £80 at MB for a sender!

Is the thread M12? Need to assemble the bits before I remove the sender as I'll be stranded at that stage.

Any other sources of senders? GSF quote £25 ish for "the pressure switch", which I suspect is not the correct component.
The lack of rattle/tap/knock/squeal noises is comforting.

 

[deejaybee]

I have a similar thing with my SL320; guage appears to read correctly when revs over 1000rpm, but below this the reading randomly bounces up and down. I'm fairly sure it is either the sender or a dodgy electrical connection somewhere, but I haven't got around to fixing it so far.

Partsformercedes do a replacement sensor for £32, so that might be worth trying?

 

[television]

Colin at MBS confirmed mine when he screwed in a normal gauge

 

[SNST]

Dave,

I checked the Partsformercedes site & can only find the level sensor. Am I missing something?

The gauge doesn't bounce around, but behaves as though the pressure just collapses as the revs reduceand recovers almost as rapidly.

Since I haven't heard any degradation, I'll take a day or two to check whether the symptoms develop.
I've managed to postpone the 200 mile trip!

 

[spock500]

I took mine out as part of the rebuild.

The pressure hole is very small but I managed to syringe it through with white spirit. As yet untried but will be firing up the engine in the next day or so, will keep you posted.

 

[grober]

Could just be a dodgy electrical connection carefully remove the connector clean it up/ spray with a water dispersant and try again. has your engine wiring loom been replaced?

 

[SNST]

Yes, although I don't know if the leg to the sender was involved - I've seen mention of it as the "positive loom" I think.
Access looks v.difficult. I assume the connector prises off. But low readings are less likely than high readings with poor connection. Tell me if I'm wrong!

There are a couple of wires & the throttle cable obscuring clear access to the sender from the top. Is it better to go in from below?

Is it reasonably safe to assume that if:
a. there is no untoward noise, with probably 200 miles done since the problem started
b. there is quite a substantial amount of oil spraying around the cams

that there is a high probability that the pump is working satisfactorily and the problem is with the sender/cabling/display?

I have to keep my fingers crossed in the short term.

Anyone know of other suppliers at reasonable prices?
I have one ordered from GSF, but I suspect it will not be correct!

 

[deejaybee]

re partsformercedes, you are right, it is the oil level not oil pressure sensor that is listed. But always worth giving them a call as they do parts that are not listed on the web site.

 

[television]

A 0065429417 SENDER UNIT,
Oil pressure gauge

 

[SNST]

I'll post later when I have the GSF kit.

Does anyone have any negative experience of this part from GSF?
The image on their site looks correct.
They will be charging about £21. (& I'm a bit suspicious!)

 

[television]

That is all it is worth

 

[wireman]

The sender presents almost zero ohms at low pressure, the gauge will read full scale if the wire is disconnected or zero if there is a short, from memory methinks its about 300 ohms at 3 bar.

 

[tjamesbo]

Similar symptoms to mine , It was the sender I checked the guage with resistors to simulate the sender

OK the resistors have gone onto the wire, and other end connected to earth results as follows;
10ohms = O bar Checks out OK
180 Ohms =3 Bar Checks out OK
68 ohms = 1.5Bar previous posts suggest this should be 2 Bar although check resistances were not quoted for the M111 engine

All readings Rock steady and same from ignition on to running no variation with revs so Voltage obviously stable .

Conclusion on basis of above favours the replacement of the Sender Now
£35 from Euromerc is favourite .
Access to the 17mm Nut at the back of sender is very poor even a stubby wrench has only about 1cm movement . I have ordered some crows feet wrenches . Hopefully these will fit otherwise I am going to have a job cracking it off ( and tightening the new one ) .

Slim good qualityCrows foot did the job

 

[SNST]

So far....

Prised off connector from top..OK
Cracked joint with 17mm o/e spanner from top. Then undid by hand only from underneath - no spanner required. All easier than I expected.

Fitted pressure gauge, ran engine for 20mins at idle, oil temp in sump 50C,
Pressure 2bar. Quickly up to 5bar with a few revs.

I 'll have to take it out on the road to get oil temp up.

 

[SNST]

Pressure stable at 2-2.5bar, so I fitted sender & all working well. Thanks to all for input.
So far the GSF sender (Topran) has performed satisfactorily. If it fails, I'll post again.

Notes:
Access from both top & underneath needed.
Undo coolant hose at Tee, then clip back out of the way.
Prise off wire connector with flat screwdriver.
Sender joint only needed o/e spanner to crack the seal, then can be undone by hand. No need for crows foot in this case. Easiest access for spanner from top. Similar technique to refit, but initial line-up of sender easier from below.

 

[SNST]

Still performing well after 15k miles.

 

[w124nut]

I had similar problems with my W124 engine oil pressure. The pressure was below 1 at idle but rose to 3 when accelerating etc. I say it was a problem as previously it was normal for the gauge to read 2 to 2-1/2 at idle.

I went to my indy who replaced the sender, checked the oil and oil filter; there was no change. The oil pressure at idle remained low.

After discussion it was decided to check the oil pump, so off with the sump pan and pump. The photos below tell of what was found.

The internal workings of an oil pump, note the scoring of the housing





The badly scored impellers



With the car stationary at idle, the instrument readings after new oil pump fitted - after a 90 mile run from the workshop. The needle of the oil pressure gauge is now where it was previous.

 

[spock500]

Crumbs, any ideas what caused the scoring? looks pretty low milage too.