Flickering engine oil pressure

[TheoK]

Once I start the boat when the engine (Volvo Penta AD41)is cold, oil pressure is fine at about 4-6 bar.
After it warms up, during throttle application and in gear,oil pressure is at mid point about 4.5 bar.
HOWEVER after cruising for about 15-20 minutes, upon immediately bringing the engine to idle,the oil pressure drops very much to almost less than a bar, and at the same time the oil pressure warning light and buzzer flicker for 5 seconds. By raising slightly the revs (out of gear) the buzzer stops and pressure rizes to about 2-3 bars. (sea state conditions being fine)The boat was then removed from the sea, for drying, annual service and antifouling, being returned to the water last week.During the time that I kept it on shore every month the engine was started and run for15 minutes
every time.Once I took the boat out after cruising/running fine for 20 minutes and coming to a rest, the engine oil pressure dropped to less than a bar and the oil pressure warning light and buzzer were loudly and fully engaged.
I immediately raised the revs slightly for 5 minutes, they stopped, then returned to idle. (sea state being fine)
The buzzer/warning light remained off, however pressure was about 1.5 bar.Im very worried NOT to damage the engine.
My mechanic, immediately re-changed oil, of the same type, and installed a bigger oil filter.
I test drove the boat again. After 20 minutes cruising, coming to rest and returning to idle,the warning light/buzzer flicked for 2-3 seconds, pressure indicated at about 2 bar.
Now my mechanic has suggested that perhaps I have a partially blocked oil cooler.
He will proceed to clean it to see what happens.
Kindly advice me on your thoughts about the matter. Is he correct, or should I be thinking that major engine overhaul
time is knocking on my door? (and wallet!)

 

[jaws]

I'm not an expert but it's probably more likely to be a faulty sensor. I had a similar problem with my previous boat with Volvo AD31. The oil pressure needle went off the scale at high revs.

 

[ostria]

I would take the following steps:
1) Change oil and filters to the original volvo suggests (and sells)
If problem persists
2) Change oil-pressure sensor
If problem persists
3) Consider engine overhauling.

 

[TheoK]

I thought about it, however it is not probable to be a faulty sensor,since there is one sensor for the oil pressure switch and another sensor for the warning light/buzzer.Both wrong at the same time?

 

[DAVIDO]

What about the oil pump.

 

[TheoK]

That is what am afraid of, so I want to elliminate all other
possibilities first.

 

[chuckaduck]

Dont kid your self

the engine has had it

As a mechanic for 25 years I know

you will need a full rebuild with crank grind etc

 

[TheoK]

Thank you for the straight forward reply.
The engine has only 590 hours.
Does not consume oil, was never cooked.
Isn't it too soon for rebuilt?

 

[macnorton]

I would check the oil pressure relief valve, these can stick open or wear out. or a said check the sender unit.

If not these it looks like open wallet sugery /forums/images/graemlins/frown.gif

 

[Cliveshep]

Why not try a simple alternative first before major strip and expense? Get a bog standard oil pressure gauge and pipe/fitting from a scrap yard and screw it into the the oil pressure switch tapping and see what reading you get? (Old fashioned type I mean)

 

[chuckaduck]

Difficult to say why but can be various power boats tend to be thrashed and they also spend long times without being used sometimes a crystal deposit can accrue in the big end bearings causing friction and wear as well you cannot garantee the hours

my advice is change the iol filter and pressure senders and see

my experience says that it wont improve but it is a cheap way to eliminate the obvious

 

[pheran]

With all due respect to your engineering experience and expertise, I'm surprised you think the engine is knackered, since with only a slight increase in revs, it achieves 2-3 bar and pressure is up to spec at normal working revs. Some wear perhaps, for the reasons you have given but I would guess its a long way from the total rebuild stage. Indeed, according to the manufacturers of my last boat's engines, anything in excess of 0.75 bar at tick-over was acceptable

 

[Dave_Snelson]

As said, check sender units. They can and do fail - both of mine did! Then pressure relief valve.

 

[TheoK]

Thanks for alarming me to the relief valve scenario.
Is this valve situated externally or inside the engine?

 

[oldgit]

Hi theo,just to say that my 40As havr got nearly 3000 hours on the clocks and use virtually no oil between yearly 150 hour oil changes.Fingers crossed expect to see 5000 before any work needs doing.

 

[fisherman]

[ QUOTE ]
Why not try a simple alternative first before major strip and expense? Get a bog standard oil pressure gauge and pipe/fitting from a scrap yard and screw it into the the oil pressure switch tapping and see what reading you get? (Old fashioned type I mean)

[/ QUOTE ]

Yes, this is what I did, the pressure was fine , the sensor was wrong

 

[ExcaliburII]

Whilst not familiar with this engine at all, if it has separate sensors for the pressure gauge and warning light, and they both agree the oil pressure is low, you can be pretty sure the oil pressure is low. As others have said, they won't both fail at the same time, and certainly not in such a way as to give the same (wrong) symptoms.

I would put my money on the oil pressure relief valve being stuck open. Don't know where it is, but when you find it there will probably be a bit of crud stuck in it. Good luck.

Oh, and FWIW, if it was mine, I wouldn't want to run the engine again until the valve has been checked.

 

[DoubleVision]

Just read this thread with "deja vous" If you check my previouse posts you will see I had exactly the same problem.
I would bet a large amount of money that your problem is the oil pressure relief valve situated under the oil cooler. Its a shame you are so far away asI would do them for you. My engines now run at 85psi at cruising revs and never drop below 30 on tickover in gear. Please dont be pushed into an engine rebuild until you have replaced these relatively cheap items. Have a look Here The items you need are no`s 1 to 7. Cost about £80 per engine. Good luck and believe me I know what a worry it is.

 

[robinstall1]

Check your wire connections, vibrations change on you engine at different revs, if you have a intermittent connection who knows!! check it out

 

[TheoK]

Thank you very much for info and drawing!
Will proceed as adviced and let you know!