Oil pressure on a mercedes om636

[stav]

Having done some searching I still have some nigelling questions in my mind and having come to the conclusion I will keep her and not get something smaller just for me I wish to get a handle on the situation with my engine.

It is the original engine from 1977 but was rebuilt in 1996 but I have no idea what was done. It is a nice colour and has an oil cooler. The hours gauge reads 3600 hrs (ish).

It starts quite well turning over only a couple of times before starting. When the enngine is cold the oil pressure is 40psi and steady whatever rpm. As the engine reaches temp at 1800rpm and above, I normally run at 2200 rpm, the oil pressure shows 40psi, as I throttle back it steadily drops so at 1500rpm has 30-35psi and at then at tick over drops to minimal and hardily readable 5psi?. In the manual it says idling pressure can be low but I can not remember if it was 1 bar or 1psi...

The oil is carlube 15w40 mineral and has been given three oil changes in the last year as I suspect it might not have had much use for three or four years and not many oil changes.

So can I live with this oil pressure? Could some pressure relief valve be operating too soon? wear in the oil pump? If I can just stop feeling anxious about it will the enigine contiune for 5 or 10 years or will it suddenly start knocking?

What jobs could I build in to the winter schedule to improve things?

As always thank you in advance.

 

[penfold]

Oil pressure gauges are often rubbish; unless it's been calibrated, all it's telling you is that there is oil pressure.

 

[lynall]

Carlube is pretty low rate oil.
Decent priced oil motor factors Comma or see what they recommend


Lynall

 

[Latestarter1]

Having done some searching I still have some nigelling questions in my mind and having come to the conclusion I will keep her and not get something smaller just for me I wish to get a handle on the situation with my engine.

It is the original engine from 1977 but was rebuilt in 1996 but I have no idea what was done. It is a nice colour and has an oil cooler. The hours gauge reads 3600 hrs (ish).

It starts quite well turning over only a couple of times before starting. When the enngine is cold the oil pressure is 40psi and steady whatever rpm. As the engine reaches temp at 1800rpm and above, I normally run at 2200 rpm, the oil pressure shows 40psi, as I throttle back it steadily drops so at 1500rpm has 30-35psi and at then at tick over drops to minimal and hardily readable 5psi?. In the manual it says idling pressure can be low but I can not remember if it was 1 bar or 1psi...

The oil is carlube 15w40 mineral and has been given three oil changes in the last year as I suspect it might not have had much use for three or four years and not many oil changes.

So can I live with this oil pressure? Could some pressure relief valve be operating too soon? wear in the oil pump? If I can just stop feeling anxious about it will the enigine contiune for 5 or 10 years or will it suddenly start knocking?

What jobs could I build in to the winter schedule to improve things?

As always thank you in advance.

OM 636 was a real nice motor but not built to particularly tight tolerances.

As another poster has commented you need to understand if the numbers you are seeing are real. Fit a mechanical gauge. Another important point is your idle speed (please do not use the term tickover). When engine was re-built the idle speed may have been set too low, check with a hand held techo, cheap a chips on Ebay these days. Suspect you need 700/750 rpm, however important that the final idle speed is where engine feels happy and gear shifts not too jerky.

Lube oil you are using is fine, changing even a poor lube as frequently are you are is giving good protection. Changing brand will not improve the situation, lube certainly has not gone into shear.

 

[david_bagshaw]

We had 2 x om314, so similar era

I would put a heavier oil in , such as a 20,/ 50 as was common in the era.

Your running pressures sound about right and the thicker oil would help on tickover.

 

[ffiill]

The OMC 636 is actually a well engineered engine-long stroke slow revving indirect diesel with its origins in the ww 2 Vermacht truck engine.
Fitted to Mercedes cars up to the late 1960s and the Mercedes Unimog 4x4 as well as the power unit for the ThermoKing refrigerating compressor fitted to artics.
It operates at a very high start up oil pressure of about 115 psi and in the case of my origional 1978 model operates at about 80 psi hour after hour at about 1800 rpm.
I have had problems with the fitted oil pressure sender units;temperature sender units and rpm sensors so before you assume its a knackered engine check out the oil pressure properly.
If the pressure read outs are right then you do have a mechanical problem as 40 psi is what mine reads on idling tick over when put out of gear.

 

[stav]

Thanks for the replys guys will invest in a tacho to check idling speed but she goes in and out of gear nicely. I will also look at a mechanical gauge even if I plumb it in temporailly. Then hopefully I will try not to worry too much.