Periodic Oil Pressure Alarm at around 1800rpm, Volvo Penta D1-30

[BrettB]

One of my Volvo Penta D1-30 diesels gives a period oil pressure alarm/light at around 1800rpm. If we keep it under, no problems at all. Unfortunately, we just have idiot lights. Any recommendations as to what I should have a look at. Thanks!

[a64pilot]

Very first thing I would do is add a temporary pressure gauge to determine if the low pressure is real or not.
I’d do this ASAP

[Tkeeth]

Definitely a64 has a good thought. If it proves to be false, I had a strange ghost alarm on a volvo that only appeared at low rpm...sometimes oil, sometimes charging. After much testing and trouble shooting it turned out to be the ecm that houses the lights, and it was expensive!!

[Wotname]

Originally Posted by a64pilot

Very first thing I would do is add a temporary pressure gauge to determine if the low pressure is real or not.
I’d do this ASAP

Agree
The second thing I would check is for damage (chaffing etc) to the wiring harness.
Third thing; swap oil pressure sensors between your engines.

[billknny]

This is the second engine TODAY I have heard about with low oil pressure at higher RPM and good oil pressure at low revs...

Other than instrument problems (ruled out already in the other case) and MAYBE low oil level in the sump, has anybody a likely scenario for this happening?

[Gingerbread Man]

Complete Newbie here (CF), and to sailing in general.
This symptom (low pressure idiot light signal as rpm rises) is occasionally seen on cars and trucks, as a result of a poor connection between the wire terminal and the pin on the oil pressure sender on the engine. Vibration causes a poor connection and a false signal.
A64 is correct, if at all possible attach a mechanical gauge before any further operation.
If that is really impractical, perhaps try confirming that the connection between the wire and the sender is clean, and maybe even squeeze the connector a tiny bit tighter (assuming either round sleeve that slides over a round post, or more likely a female spade terminal on the wire and a male spade on the sender.) This may solve the issue, if not you must shut down immediately and test properly as per A64 and a manual, because (almost?) any legitimate cause of losing pressure as rpm rises will cause catastrophic failure very quickly, even as the engine is run below where the alarm sounds.
Hope this helps, and does not lead you towards further engine damage.

[Wotname]

^^
Gingerbread Man, Welcome aboard CF.
What you say generally applies transducers (sensors) for oil pressure gauges but not so much to transducers (sensors) for oil pressure alarms (idiot lights). Faulty alarms are more often due to short circuits in the wiring or faulty sensors rather that open circuit or high resistance wiring issues.

However as the OP has twin engines, he has a good opportunity to swap sensors to confirm their operation (good or bad).

[Gingerbread Man]

Wotname, you appear to be correct. My advice for a possible solution is flawed and should be disregarded. I do stand by my advice not to run it any further without a mechanical gauge, or possibly swapping senders as Wotname has suggested. Are the senders known to fail?

I did a quick search before posting and thought I had identified the correct sender. After your post, I looked a little deeper to discover that the sender I identified is used with gauge and alarm, and the light only type sender that I can find is, as you say, a normally closed switch that would not behave as I suggested.

ps. The V-P manual I referred to for this information actually calls it a normally open switch during normal operation. Strange nomenclature.

[Wotname]

Originally Posted by Gingerbread Man

Wotname, you appear to be correct. My advice for a possible solution is flawed and should be disregarded. I do stand by my advice not to run it any further without a mechanical gauge,

Very safe approach and has much to recommend it!

or possibly swapping senders as Wotname has suggested. Are the senders known to fail?

Only occasionally and only sometimes intermittent (vibration related) but it an easy thing when you have a known good identical engine nearby and I do like to do the easy things first!

I did a quick search before posting and thought I had identified the correct sender. After your post, I looked a little deeper to discover that the sender I identified is used with gauge and alarm, and the light only type sender that I can find is, as you say, a normally closed switch that would not behave as I suggested.

ps. The V-P manual I referred to for this information actually calls it a normally open switch during normal operation. Strange nomenclature.

There is no accounting for what V-P does

[Roger L]

Originally Posted by billknny

This is the second engine TODAY I have heard about with low oil pressure at higher RPM and good oil pressure at low revs...

Other than instrument problems (ruled out already in the other case) and MAYBE low oil level in the sump, has anybody a likely scenario for this happening?

Yes. It isn't unknown for oil pressure to drop as RPMs go up when there is a restriction in the feed to the pump. That causes cavitation in the pump which will destroy one in short order. It is worth looking into. Could be anything from a pinched hose, or a crudded-up oil pickup in the oil pan. I've also heard of this problem happening because someone decided to add a filter on the low pressure or feed side of the pump.

Certainly I'd check it with a gauge first to make sure the pressure drop is real. Just saying that there are real mechanical reasons for pressure to drop at higher RPMs - and the pump intake is where to start.
rScotty

[Zoidislander]

The Harbor Freight oil pressure tester gets good reviews. $24.99. The kit should have all of the adapters that you need for your Volvo.

[Cadence]

Originally Posted by BrettB

One of my Volvo Penta D1-30 diesels gives a period oil pressure alarm/light at around 1800rpm. If we keep it under, no problems at all. Unfortunately, we just have idiot lights. Any recommendations as to what I should have a look at. Thanks!

Replace the sending unit.

[georgeg305]

Regarding putting a oil pressure gage on your Volvo Penta engine to monitor the actual oil pressure. Before you start, you need to determine what the thread size is for the oil pressure sensor hole in the block.

The American Standard is called National Pipe thread ( NPT ) which calls out the pitch and taper of the thread in the hole. American oil pressure gages come with an NPT connector

I have NO idea what thread the Volvo engine is tapped with. My Westerbeke M-25 oil pressure port is tapped with Japanese Industrial Standard ( JIS ). Fortunately JIS is compatible with British Pipe thread ( BPT ). NAPA sells an adapter ( 2 ) for converting from NPT to BPT, or vice versa.

There are also Metric threads around that are "different"

[boeing1]

when is the last time the oil and filter was replaced,

[seasick]

Two possibilities come to mind.
The wrong oil viscosity has been known to cause
this pressure switch to close at prematurely or rather
when it shouldn’t be.

The other possibility is that your oil pressure relief valve
May be opening prematurely.

Swapping out your senders as mentioned may be telling
but if you’re experiencing the same issue with the other transducers
I would double check that the correct oil has been used then check the oil relief
valve.

See part #16