Topic: BMC1.5 fluctuating oil pressure

ruby    -- Aug-20-2016 @ 7:43 AM
  Hi any advice would be appreciated. My ex hire boat has a venerable 1.5 Bmc Diesel engine. It starts first time hot or cold and runs with very little smoke. When cold it runs at 50 psi which I understand is correct. At 1600 revs it drops to about 25 psi after an hours running and then to about 12 psi after two or three hours. On tick over at this point it drops to 1 or 2 psi.  We have owned the boat for three years , had the engine serviced annually and completed about 100 hours running during that time.  We last used it this week when it ran for 14 hours over three days. The engineer suspected a faulty sensor or gauge last year but these were recently changed to new units  and the oil pressure fluctuation has remained the same. Do people think I am likely to have a problem or is it just one of those things . Thanks in anticipation


waterbuoy    -- Aug-20-2016 @ 8:04 AM
  I suggest you take a look at this thread

It contains a number of ideas.


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ruby    -- Aug-20-2016 @ 8:18 AM
  Hi Clive

Thanks for this. It looks like I need to check the lift pump issue . As far as I remember we have never had a problem with diesel in the oil but I have not checked it either.

Thanks again


ruby    -- Sep-2-2016 @ 7:02 PM
  Just to let everyone know we did have diesel in the oil and we have had the lift  pump replaced ( even though it was nearly new ) and the oil pressure seems to have stabilised.

A useful tip for others is to put a cable tie round the dip stick at the point where the engine is full of oil and the dip stick is measuring maximum. If you just let it clunk to the bottom ( as I know many people do ) then it is not very easy to see whether there has been a sudden increase in oil . Or should I say oil diesel mix.

Thanks for the helpful clues.


Ps the thread should of course say BMC not Bec oil pressure

spiderman    -- Sep-5-2021 @ 9:33 AM
  Morning All.
My oil pressure gauge has started fluctuating fairly rapidly on first start up for around a couple of minutes, then settles steady slightly lower than normal.
Oil appears normal with no increase in amount up the dip stick, so I thought I'd start with an oil and filter change.
In the manual it recommends several different grades of oil so I thought I'd ask what the general consensus is for the best oil for the good old BMC.
I'm sure that will bring many different answers, but if you think a particular oil  that might help this particular problem I would be most grateful.

annville    -- Sep-5-2021 @ 11:37 AM
  Hi On the side of the block there is a large domed cap above the oil filter housing undo this nut carefully under there is a long spring on the end is a aluminium piston this seats on a recessed face, this controls the oil pressure they can get stuck/with debris remove inspect it may need lapping in a close inspection will reveal all. John

spiderman    -- Sep-5-2021 @ 2:12 PM
  Brilliant, thank you for that.
Can I ask what you oil of preference is please?

annville    -- Sep-5-2021 @ 5:32 PM
  Hi Spiderman I use Castrol inboard 4T 15W/40 marine engine oil part no SKU 00010472  not cheap but it has additives to help oil to cling to engine surfaces plus anti corrosion inhibiters when engines stand for long periods you can get it from  OPIE Phone 01209202944 they are at Redruth,  it comes in 4lt cans John

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