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Old 11-05-2014, 10:31   #1
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BMC 1.5 oil pressure problem????

Hi guys, I put a question on here a while ago regarding my Perkins 4. 108 that had no oil pressure. Since then a friend if mine has asked how I managed to troubleshoot the issue as he has issues of his own. Essentially, when he starts his BMC up, the pressure gauge goes right round to the highest pressure, then drops back slowly as the engine warms up. His oil is clean and filters are clear. Ideas?
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Old 11-05-2014, 11:19   #2
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Re: BMC 1.5 oil pressure problem????

Motor traders have been known to put gear oil in old bangers' engines to make pressure at the gauge look normal. Increasing spring tension in the relief valve can have the same effect.

Suggest he has it checked out by someone who knows that engine - plenty still on the canals I think - and taxi mechanics will know them well from the bomber days.

I'm only theorising here... but a dodgy head gasket might let cylinder pressure into the oil gallery, might even cause a runaway. Not sure, don't know that engine at all.
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Old 11-05-2014, 11:49   #3
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Re: BMC 1.5 oil pressure problem????

What is the "normal" position of the sender/gauge combo? Meaning when power is off to it/them.

If the gauge/sender, with the engine off, stays high, then it simply means that it will start reading lower and at operating range, only once the engine starts. Odd but I've seen stranger things...
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Old 11-05-2014, 12:05   #4
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Re: BMC 1.5 oil pressure problem????

When ignition is off, needle goes to 0. When he starts up, it goes all the way over the high, then slowly drops as the engine warms up to normal running pressure.
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Old 11-05-2014, 12:25   #5
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Re: BMC 1.5 oil pressure problem????

Check the oil pressure relief valve - check that it's not stuck closed (although stuck open is probably more common). Also look at the oil system layout and the position of the guage sender and see if a partly blocked gallery or line might cause a high pressure reading when the oil is cold.

And check that the oil pressure gauge/sender is working correctly.
Good Luck.
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Old 11-05-2014, 12:32   #6
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Re: BMC 1.5 oil pressure problem????

If the pressure gauge is electromechanical - ie has a wire to the back, not a tiny tube - It might just be the sender unit on the engine block.
Needle jumping around or not moving are the failure modes that I remember but it has been a very long time.
Best to resolve the issue even if your friend has to rent a mechanic.
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Old 11-05-2014, 13:13   #7
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Re: BMC 1.5 oil pressure problem????

If it really does have high pressure, the relief valve near or in the pump is sticking. Pretty rare problem and I would double check with a mechanical gage before I did anything.
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Old 13-05-2014, 01:25   #8
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Re: BMC 1.5 oil pressure problem????

I will pass this across and post updates when I get any. Thanks guys!
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