VP AD41B Idle Reduced Oil Pressure

[orion1210]

Hi all, hoping I can tap into the collective wisdom and experience on here.

My port AD41B suffers reduced oil pressure at idle when hot, stable around 15-20 psig, but can trip the LP switch if I come off the plane and to idle too quickly. Picks back up with a little bit of throttle. I suspect from observing indicated oil pressures at various rpms that something is going on the with the piston cooling valve. This engine also takes longer for the coolant to warm up, possibly because the oil is taking some additional heat away at a guess.

I’ve finally got around to pulling the oil cooler/filter assembly off hoping to find something obvious. The only two observations:
1) there was a bit of ‘grit’, approx 3mm, stuck fast on the piston cooling valve seat exactly where the valve would contact.(assumed from when previous owners had the cooler repaired, opened filter paper is spotless thankfully)
2) both valve seats have an approx 1-2mm chamfer where the valve would contact.

In your experience do you think that the 3mm opening on the cooling valve could cause this low idle oil pressure?

Should I worry about the slight chamfers on the valve seats reducing the spring pressure and therefore reducing oil pressure slightly?

Thanks

 

[oldgit]

Seem to recall spending much time worrying over the the apparent low oil pressure on idle on high hours 40A and then high hours 41B engines.
After few thousand hours in both boats internet research suggested that it was just par the course for these engines.
At high engine revs the oil pressures were "good" and when coming back to idle after a run the temperatures soon dropped and the oil pressures stabilised.
However in both instances both engines gave the same oil pressures at low idle.
In both instances one of the engines always ran at a small higher temperature than the other , never did discover why.
Doubt it was much to do with the calorifier.

 

[BruceK]

For your turbo sake its good to come off the plane at a measured pace. You'll find the pressure will also decrease then at a measured pace. On the oul cooler the valves are super cheap and easy to replace so no harm in replacing them if in doubt

 

[Montemar]

If the grit held the valve open slightly then some pressure must have been lost

 

[orion1210]

Should it help anybody else; my low oil pressure was casued by a partial obstruction of the raw water inlet pipe immediately before the pump. An impellor must have lost some blades in the previous owners care and perhaps suprisingly were pushed against the incoming water flow and jammed in the pipe out of sight. As soon as I removed them the oil pressure returned to as expected. I guess the hot oil was thin enough to drop the pressure at low rpms, strangely didn't have any coolant overheat issues though.

 

[oldgit]

Usually the water to the pump comes directly from the sea cock,possibly via a filter, if the impeller blades strip off they will be be carried out of the raw water pump and settle in the next thing in the system the oil cooler, the blades usually gather in the little chamber at the front , being unable to pass through the cooler matrix tubes.
The front plate can be removed with care or removing the pipe, a hose with mains pressure will flush out anything in the chamber.
Do know of blades jamming in the exit hole in the impeller pump but never so far at the inlet ?

 

[orion1210]

I can only speak for AD outdrive installations where the strainer is immediately down stream of the pump. No impeller blades were found there, opposite to expectation. I guess the rotation of the remaining impeller forces any liberated blades down against the water flow and then in my case perfectly tessellated to form a secure partial blockage.