What causes a drop in oil pressure

[Colvic Watson]

One problem solved is another problem found at the moment. Now that the engine senders and control panel are fixed, there is according to the mechanic:

an oil pressure drop once the engine is put through a higher rev range

Another test will take place tomorrow but has anyone got an insight before we do it? The engine is a Thornycroft 230 approximately 75hp, the engine dates from 1977.

Thanks for any help and advice.

 

[Slipstream 34]

One problem solved is another problem found at the moment. Now that the engine senders and control panel are fixed, there is according to the mechanic:

an oil pressure drop once the engine is put through a higher rev range

Another test will take place tomorrow but has anyone got an insight before we do it? The engine is a Thornycroft 230 approximately 75hp, the engine dates from 1977.

Thanks for any help and advice.

Either a faulty pressure relief valve or a leak.

 

[GrahamHR]

................and even too much oil; it can get whipped up into a froth by the crank and the effective viscosity drops.

 

[Colvic Watson]

Thanks for the comments so far - will suggest a master gauge test but the gauge is new and works at low to almost top revs.

The engine is so darned powerful we have never used it above 70% revs even against a nasty tide. Does the drop in pressure matter? (assuming there is no oil leak).

Wrong grade of oil - checked at oil change

oil overheating, oil cooler not working - happens from cold, could this still be an issue?

Worn out oil pump - refurbish or replace - Estimate - any ideas?

Worn main and big end bearings - regrind bearings renew shells - go on then, how much. Make me cry

pressure relief valve sticking - renew - some times you can repair them - how deep in the bowels is this? A big or a small job? Why doesn't it drop the pressure at low revs as well?

 

[pappaecho]

This may sound a bit simple. What is the "normal oil pressure" and the "reduced"
I assume that the pressure is transmitted by an oil pipe, rather than an oil pressure system which relies on resistance to read out on the oil pressure meter.

If the meter is connected by a pipe, it could be air in the pipe giving a false reading.

If the latter system, then again air could be a problem, but more likely isa faulty sender.

Before you look at bearings, oil pumps etc, I would try by substitution the meter and the sender, as they are still the most likely cause.

Years ago I had a failure of a similar nature. I asked if it was safe to run the engine, and was told to look at the rockers - if oil was flooding via the rockers, the oil pump was ok and the meter or sender was u/s. It was the sender.

Good luck

 

[DownWest]

Bit odd, this one. Relief valves usually stick open, so low pressure at low revs. Same for rest of probs. If the relief valve sticks closed, big pressure at high revs.
If it was me, I would put a mech gauge (not electric) on and try again.
Had a couple of probs recently due to worn pumps. But, OK at higher revs, light coming on at tick-over.

A real long shot... Might the oil strainer be blocked, and restrict the flow to the pump at higher RPM?
DW

 

[pappaecho]

This may sound a bit simple. What is the "normal oil pressure" and the "reduced"
I assume that the pressure is transmitted by an oil pipe, rather than an oil pressure system which relies on resistance to read out on the oil pressure meter which si electonic.

If the meter is connected by a pipe, it could be air in the pipe giving a false reading.

If the latter system, then again air could be a problem, but more likely is a faulty sender.

Before you look at bearings, oil pumps etc, I would try by substitution the meter and the sender, as they are still the most likely cause.

Years ago I had a failure of a similar nature. I asked if it was safe to run the engine, and was told to look at the rockers - if oil was flooding via the rockers, the oil pump was ok and the meter or sender was u/s. It was the sender.

Good luck

 

[Heckler]

Thanks for the comments so far - will suggest a master gauge test but the gauge is new and works at low to almost top revs.

The engine is so darned powerful we have never used it above 70% revs even against a nasty tide. Does the drop in pressure matter? (assuming there is no oil leak).

Wrong grade of oil - checked at oil change

oil overheating, oil cooler not working - happens from cold, could this still be an issue?

Worn out oil pump - refurbish or replace - Estimate - any ideas?

Worn main and big end bearings - regrind bearings renew shells - go on then, how much. Make me cry

pressure relief valve sticking - renew - some times you can repair them - how deep in the bowels is this? A big or a small job? Why doesn't it drop the pressure at low revs as well?

Interesting "happens from cold" Usually worn engines (bearings) have pressure when cold, the oil is "thick" and doesnt flow out of the spaces so easily and the pressure guage reflects that, so if worn, pressure drops as it heats up.
Stu

 

[Heckler]

Bit odd, this one. Relief valves usually stick open, so low pressure at low revs. Same for rest of probs. If the relief valve sticks closed, big pressure at high revs.
If it was me, I would put a mech gauge (not electric) on and try again.
Had a couple of probs recently due to worn pumps. But, OK at higher revs, light coming on at tick-over.

A real long shot... Might the oil strainer be blocked, and restrict the flow to the pump at higher RPM?
DW

I had a prob with the oil pump pickup guaze getting blocked with "varnish" flakes on a failrly new suzuki pickup, similar symptoms. I would check with a mechanical guage direct and if the same, drop the sump
Stu

 

[Colvic Watson]

I had a prob with the oil pump pickup guaze getting blocked with "varnish" flakes on a failrly new suzuki pickup, similar symptoms. I would check with a mechanical guage direct and if the same, drop the sump
Stu

Why don't you work on the East Coast?

 

[sailorman]

Why don't you work on the East Coast?

I thought Tom woz the DBs

 

[DownWest]

Dropping the sump might be a big problem in his boat..
DW

 

[Colvic Watson]

I thought Tom woz the DBs

He's da man. But SkipperStu sold me the world's most reliable eberspacher for £200 and always seems to suggest simple ideas for fixing probs. Tom did a major league job on the stuffing glad today, just wish the list of problems would actually stop

Still, if SkipperStu is reading this thread and is swayed by flattery I'd like another one of those £200 ebers please!

 

[Colvic Watson]

Dropping the sump might be a big problem in his boat..
DW

Too right, there's a two foot drop underneath it, it would make a hell of a clang.

On a serious note, are you suggesting a sump clean?

 

[sailorman]

He's da man. But SkipperStu sold me the world's most reliable eberspacher for £200 and always seems to suggest simple ideas for fixing probs. Tom did a major league job on the stuffing glad today, just wish the list of problems would actually stop

Still, if SkipperStu is reading this thread and is swayed by flattery I'd like another one of those £200 ebers please!

eber,ask Photodog he might have one for sale

 

[DownWest]

Too right, there's a two foot drop underneath it, it would make a hell of a clang.

On a serious note, are you suggesting a sump clean?

Sort of, if the oil strainer is in the sump, which seems a reasonable assumption on an old donk like that. Can't immagine the access tho...
DW

 

[Heckler]

He's da man. But SkipperStu sold me the world's most reliable eberspacher for £200 and always seems to suggest simple ideas for fixing probs. Tom did a major league job on the stuffing glad today, just wish the list of problems would actually stop

Still, if SkipperStu is reading this thread and is swayed by flattery I'd like another one of those £200 ebers please!

Yo!
prob is the supply has dried up, he got wise to their worth!
Stu

 

[GrahamHR]

I had a prob with the oil pump pickup guaze getting blocked with "varnish" flakes on a failrly new suzuki pickup, similar symptoms. I would check with a mechanical guage direct and if the same, drop the sump
Stu

I just remembered a similar thing; Escort Mexico in the early 1980's, newly rebuilt engine fitted on a Thursday, driving across from Holywell to Wrexham on a Thursday night to pick up my fiancee and an engagment ring on the Friday (plus off to friends' wedding on the Saturday). Almost no oil pressure above 1,500 rpm. Engine out/ sump off at 5:00 am on the Friday, bent (brand new) oil pickup diagnosed ( almost touching the sump) and all remedied/ refitted. In Manchester via Wrexham by 14:00 and in the Harrogate area by 17:00 !

Still married !

 

[Trundlebug]

It may also be that some of the internal oilways are a bit blocked, slowing the return of oil to the sump once it's been pumped around the engine.

At higher revs it will be pumping the oil out of the sump quickly, but if it's not returning as fast then it will lose pressure. This will be worse with cold oil which doesn't flow as freely under gravity.

Especially if the oil level is low (which I am assuming it isn't, I'm sure it's the first thing you checked).

One idea might be to try using some of that flushing oil through the engine to clear out the years of accumulated gunk. This is a lot easier than taking the engine apart, and may also address the gauze strainer if it's an issue (mentioned above)

Then refill with fresh engine oil and try again.

 

[Colvic Watson]

Thanks for that - I've asked now the yard about the flush option.