Help!!! Oil pressure problem on diesel engine

[Kfz70]

Right, here's the problem...

 

- Engine is a 6 cylinder diesel, 4.5 litre.

- Oil pressure is reading at maximum - when the engine is turned over the oil pressure gauge goes straight to maximum and remains there when the engine has started.

- The gauge is mechanical and I've checked all the connections are OK.

- The head gasket has recently been replaced, but it was a professionally manufactured gasket and fitted in accordance with the workshop manual and manufacturer's instructions. The head was skimmed and pressure tested before it was refitted. As far as I can tell, the gasket has sealed as I'm not getting any oil in the coolant or vice versa (having said that, I've flushed the coolant through about 9 times and I'm still getting oil coming out!).

 

Anyone got any thoughts on this as I'm not sure where to go (I'll admit I'm out of my depth). Any assistance is very much appreciated (advice or physical!!).

 

Dave

[Guest catweazle (Banned Member)]

We need to know more what engine etc,has anywork been done on crankshaft,oil pump,cyl head shouldnt affect oil pressure even if it flows thro it if it was blocked would just starve rocker gear.i assume you have changed oil filter and made sure that area is ok,oil pump pressure relief valve? try another gauge first. what was the gauge reading before the work.it will take a while to clear the oil from the cooling system,we have this problem on f/lander you must use a detergent.The two may not now be linked.

[Kfz70]

Engine is a Mercedes OM312. The crankshaft and oil pump haven't been touched (though the filter has been cleaned). The sump was removed to make sure there were no bits of engine in it when the head gasket blew!

 

As far as I can ascertain there isn't a pump relief valve.

 

The gauge is somewhat arbitrary as it has no markings on it (I need to replace it really) - it was reading roughly 2/3rds of the way round before the work. If it was revved whilst in neutral, the oil pressure went shooting round to maximum but was OK when under a load. There are no problems with engine temerature.

 

I've used various detergents on the coolant system - is there anything you've had particular success with?

[Kfz70]

This is from the manual if it helps (apologies for the German!).

 

[Guest catweazle (Banned Member)]

hi is the oil cooler ,air or water cooled,if water then you may get cross contamination there,do you know if the pressure gauge is before or after the oil cooler,if before and its restricted you could have high pressure on the gauge but low at the crank.All of the detergents we have used were ok.

[Kfz70]

The gauge is fed from the lower part of the block, I think it's possibly before the cooler, but I'd have to check. The cooling is done by water - this part hasn't been touched and was OK prior to the head blowing.

 

This is the cooling system (not a very good copy I'm afraid):

[Enigma]

I presume you've got the right oil in it?

Maybe the oil is to thick?

[Tony B]

I would first doubt the gauge. If the engine has been worked on presumably it was in a poor state, then oil pressure may have been low. the next thing is is the oil relif valeve working properly, the manual should tell you how to set it. If and it seems strange, there is no relif valve, there may be an oil way blocked.

[Guest catweazle (Banned Member)]

IS it possible to bypass the oil cooler,i think you need to convince us that gauge is ok,what you have is the exact opposite to most,every one is struggling to get higher pressure on these old vehicles,i think the oil pressure fairy has given you everyone elses share.:-D

[Richard Farrant]

According to your pictures of the oil flow, there are three valves in the lubricating system,

Main relief valve 5.5 - 8 atu

Filter bypass 1 - 1.5 atu

Cooler bypass 1.5 - 2 atu

 

Are you sure the oil / water problem initially, was the head gasket? Coolers are often likely problem, hence why you still have oil in the water perhaps?

 

Richard

[Guest catweazle (Banned Member)]

 

Are you sure the oil / water problem initially, was the head gasket? Coolers are often likely problem, hence why you still have oil in the water perhaps?

 

Richard

My thoughts exactly,not familier with this engine,is the oil cooler tacked on to the block with external fittings or part of the block as on my cats ,any trouble on the latter meens deep doo doo.

[Kfz70]

According to your pictures of the oil flow, there are three valves in the lubricating system,

Main relief valve 5.5 - 8 atu

Filter bypass 1 - 1.5 atu

Cooler bypass 1.5 - 2 atu

 

Are you sure the oil / water problem initially, was the head gasket? Coolers are often likely problem, hence why you still have oil in the water perhaps?

 

Richard

 

The head gasket definitely blew - I have a picture of it somewhere. It's hard to tell if the volume of oil in the coolant is decreasing or not - there is no significant loss of oil from the sump when the engine has been run.

 

The engine itself was OK - it had been run regularly before and after I got the vehicle, in fact when it was restored the engine was only serviced as it was running fine.

 

Many thanks for all the help and advice - it's demonstrating how little I know and need to learn!

[Kfz70]

I presume you've got the right oil in it?

Maybe the oil is to thick?

 

The oil is the correct spec as per the workshop manual - it's fresh from the can!