Re: [Amel Yacht Owners] Re: Perkins M 4.154 engine repairs, rescheduling trip

James Alton

Christian Alby,

   I have never seen a problem where the oil pressure on an engine would drop as engine RPM was increased.  The only explanation that I can think of is a mechanical failure of the oil pump.  As I recall from your previous posts:

1.  Your engine experienced significant dilution of the engine oil with diesel fuel followed by at least two runaways which likely exceeded the maximum RPM rating of the engine.

2.  Apparently due to the loss of lubrication, the oil pump was badly scored.

  My guess is that due to the lack of lubrication,  high engine speed (and perhaps some galling of the oil pump which lead to the  scoring the oil pump) that something in the drive for the oil pump has mostly failed.  Perhaps the gears driving the oil pump are beginning to slip at 2000 RPM now because either the gears or the bearings that should hold the correct clearances have been damaged.  In other words the gears could be only partially engaged due to wear of the gear or the bearings and as the oil pressure rises with engine speed, you reach a point where they begin to slip, causing a rapid drop in oil pressure.  Lowering the engine RPM and oil pressure might be allowing the pump to resume turning as the load on the pump drops and the gears partially reengage.  Certainly unless this problem is corrected, your new engine will not last long.   It is of course impossible to know for sure what the problem is but given that the oil pump is essentially a positive displacement pump which should pump more oil with increasing RPM,  this is the only scenario that I can think of to cause the symptoms that you described.

Best of luck and Happy New Year,

SV Sueño,  Maramu #220

On Dec 31, 2017, at 11:38 AM, christian alby calbyy@... [amelyachtowners] <amelyachtowners@...> wrote:

Here is

Yes - oil pressure gauge and l'os pressure alarme on
When oil pressure below  1 bar, alarme nées
Oil pressure drops quickly at 2000 rpm
Oil pressure remains stable when low or normal
Oil pressure remains low when reducing speed from 2000 

No loss of oil single de started.  
Ran 1hour maneuvring in port at 1300 rpm at 2 bars, went To idle after 1 hour at 700 rpm with 1.1 bar oil pressure.
Did  not  risk acceleration. 

Thks for assiste

Christian alby - Desirade VIII - Maramu 116 - now in Mindelo Carbo Verde

Le dim., déc.. 31, 2017 à 14:58, greatketch@... [amelyachtowners]
<amelyachtowners@...> a écrit :

Losing oil pressure at high RPM and having it come back at low RPM is a bit of a puzzle to me.  There are ways it can happen, but they are a bit exotic

Do you have an oil pressure gauge AND an low oil pressure alarm?  
If so, is the gauge showing low pressure AND you get an alarm?  
Does the oil pressure drop quickly at 2000RPM or does it drift down slowly?  
Is it stable, or does it bounce around?
Does it come back quickly when you reduce the RPM, or does it stay low?

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