VM Problem

ian38_39

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A friend of mine has a bit of a problem a bit of a teaser with a 6 cylinder VM diesel engine (same as four cylinder used merc and BMW circa 96 separate cylinder heads)
Engine starts from cold and oil pressure rises straight to around 5 bar and drops to around 2bar at 750 rpm once the engine is up to temperature. Now if I stop the engine and restart after a couple of minutes all is fine and oil pressure comes straight back up but if I stop for 15minutes or more once I restart the oil pressure is zero and oil light on for around 2 minutes before going straight back up to 2 bar.
During this time there is no noise from the bearing at all.
I have tested the sender and gauge and then cracked open an oil feed banjo that feeds the rockers to confirm there is little or no oil pressure during this time. I changed the oil which had only done 1000 miles and this seamed to solve the problem on the first couple of test but still took 15 secs to record pressure on the third test. The oil is 15/40 mineral and the pump is cog driven behind the front cover.
Any one got any ideas what this could be. When the pressure comes up it stay at2 bar at tickover and rises to 5 bar when revved.
Thanks in advance
 

Elessar

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A friend of mine has a bit of a problem a bit of a teaser with a 6 cylinder VM diesel engine (same as four cylinder used merc and BMW circa 96 separate cylinder heads)
Engine starts from cold and oil pressure rises straight to around 5 bar and drops to around 2bar at 750 rpm once the engine is up to temperature. Now if I stop the engine and restart after a couple of minutes all is fine and oil pressure comes straight back up but if I stop for 15minutes or more once I restart the oil pressure is zero and oil light on for around 2 minutes before going straight back up to 2 bar.
During this time there is no noise from the bearing at all.
I have tested the sender and gauge and then cracked open an oil feed banjo that feeds the rockers to confirm there is little or no oil pressure during this time. I changed the oil which had only done 1000 miles and this seamed to solve the problem on the first couple of test but still took 15 secs to record pressure on the third test. The oil is 15/40 mineral and the pump is cog driven behind the front cover.
Any one got any ideas what this could be. When the pressure comes up it stay at2 bar at tickover and rises to 5 bar when revved.
Thanks in advance

I have a manual you can photocopy if you are near southamton. It's the same as a Mercruiser engine and was also fitted to range rovers.
Try flushing oil then refilling with fresh?
 

ian38_39

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Thanks but he has all the manuals and has flushed and refilled the oil, the whole sump was off over the winter after a piston problem so at least in February the oil system was as clean as a whistle.

The strange thing about this is that although he has confirmed that there really is little or no oil pressure when it is shown, by changing over the senders and by undoing an oil pipe, when the pressure does come back it comes straight back and does not build gradually.

from cold the pressure is there instantly and if stopped and started straight away when warm the pressure is there, it is just when the engine is warm and has stood for upwards of 10 minutes.

How much of the engine is suffering from no oil he does not know as there is no evidence of knocking or any untoward noises from any bearing for the time he has no pressure.
 

ian38_39

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Is this a unique then, looks like I lost, I bet him a post here would provide an answer. have never known the whole forum stumped before.
 

Assassin

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Sorry to be a bit vague, but from memory i cannot remember which engines had these fitted.

Many VM engines have a mesh strainer installed in the oilways, and often these break or delaminate to varying degrees, these flap over and restrict the oil flow. Once sufficient pressure has been achieved often they blow the offending part clear and allow the oil to flow properly at the correct rate and pressure.

You will need to ascertain if the particular engine has a strainer fitted, and where? this can be done by contacting VM directly and quoting the engine number.

If it has an inline strainer fitted, remove it, break it up if necessary and just ensure the engine oil is kept clean by regular changes and running up to temperature regularly so it suspends the particles as it should before it is filtered.
 

Assassin

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Had time to think about this one, what we used to do was blow out the oilways with high pressure compressed air, but in the reverse to the oil flowing direction. Often it would blow out the debris from the filter to the sump, but needs the engine partially stripped to do it.

The inline strainers were mainly fitted to commercial engines.

What we found was that the debris was mainly fibre filaments from rag which was used to clean around the engine, or the oil spills from wiping them up, this got into the engine over time and built up.
 

davedpc

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I have a pair of VM's in my boat. I've just had an intermittent similar problem with my V12 Diablo engine which is costing big bucks in spares alone. This uses a similar oil pump and it was only after i fitted a mech.guage that i could confirm that i had no oil pressure after only restarting from hot. Starting and stopping was nec. until full oil pressure was restored.The problem was not obvious as when the oil pres. went i also experienced an elect. prob. also. At first i suspected a relief valve which in any case ment me having to remove the whole lump. When the engine was stripped i found it was a oil pump bearing cage that had broken up. The out of line pump gears had been letting the air past stopping the primming action in the pump. You think boat spares are expensive? The funny thing is that the 2 pump bearings only cost £15 from the local bearing factors.
 

ian38_39

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Thank you for the reply's had not thought of the possibility of air and it does make a lot of sense, looks like it is time to get the spanners out again, will keep you informed of the outcome when hopefully it is fixed.
 
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