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Oil pressure problem?


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Started cruising today and noticed that the oil pressure guage was acting a bit odd.

Acording to notes left by one of the previous owners the guage shows around 40psi when the engine is first started and then drops to around 10 when the engine is up to temperature. Since having the boat this is pretty much what it does, although I think it usually shows between 0 and 5 psi.

Today I noticed that every time I increased the revs the needle shot up.

On tick over it shows around 3-4psi, when increased to 10k revs it was going up to around 10psi but anything over 10k revs it shot right off the end of the scale.

The guage is a Durite and shows 0-100 psi but the needle was going past this to the end stop.

This was obviously a bit worrying so I moored up and let the engine cool.

Once cool I checked the oil at it was perfectly OK.

I started the engine and the needle shot straight up to the end stop.

It may have dropped down once the engine was hot but I didn't want to risk it.

It may have been doing this for a up to a week as we have been moored for that long and the other half usually starts the engine in the morning to start the daily charge up.

I'm hoping this is just a faulty guage as the engine seems to run and sound normal.

The engine is a Lister Canalstar 4 cillinder and the guage is Durite.

 

I did top up with oil about a week ago

 

Your thoughts would be appriciated

Edited by Bewildered
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Listers don't do 10k, most diesels don't, I think you mean 1000, but anyway, I know nothing about your engine but 3 to 4 psi sounds rather low to me, have you looked at what it should be in manual?

But to answer your question....

Fault is almost certainly the gauge or sender, I have seen something similar on cars, pretty sure its the sender or just possibly a bad connection.

 

A stuck pressure relief valve can cause something a bit like this and that's more serious, but the symptoms that you describe don't really fit with that.

 

...............Dave

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1k, not 10k :)

 

If you had 100psi on a Lister it would be a miracle (and be leaking out everywhere!).

 

Either the sender or the meter has become faulty. I'd suggest the sender. OR... you have a wire chafing somewhere.

 

If you pull the connection off the sender what does the gauge do?

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1k, not 10k :)

If you had 100psi on a Lister it would be a miracle (and be leaking out everywhere!).

Either the sender or the meter has become faulty. I'd suggest the sender. OR... you have a wire chafing somewhere.

If you pull the connection off the sender what does the gauge do?

I would need to locate the sender first, no idea where it is on this engine, will have to dig the manual out.

I was hoping it would be the guage or sender, didn't think the engine would run at 150psi.

It do make you panic a bit when you notice the needle shoot up like that though.

And yes 1k not 10k, I read the guage as 10 but didn't think what multiple it was by ?

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The sender is down near the oil filler ( the one on the side not the one on the rocker cover) same side as oil filter

 

There's a right angle fitting into the side of the engine and the sender unit is screwed into that the wiring connectors are covered with a rubber boot.

 

Expect the genuine replacement to be ridiculously expensive but sounds like durite sender is needed and they should be more reasonable.

 

I'd be tempted to get a new gauge and sender from China via eBay. The thread is usually 1/8 npt ( not same as 1/8 bsp)

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Hmmm on modern engines like yours the oil pressure (or flow, more accurately) will be proportional to the engine speed. To limit the pressure they have a spring loaded bypass valve and yours just 'might' be jammed.

 

But like other posters I'd suspect the sender first, as your tickover pressure seems unnaturally low.

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I wonder if it is a mismatch between gauge and sender. There are two standards of resistances used and if you mix a gauge and sender you either get roughly half or double the actual oil pressure. Anyhow the oil pressure figures left by the previous owner look suspiciously low to me so however rare there might be an internal engine fault and I think the oil pressure relief valve in not accessed externally on that engine (happy to be corrected).

 

Because of the potential for a mismatch between gauge and sender I think I would try to get hold of a mechanical test gauge kit and ft it in place of the sender. Then you will know the true oil pressure. If it is too high then suspect the PRV jammed closed but it is very rare OR someone has used a too viscous oil. If it really does drop to 10 psi when hot then suspect a PRV jammed open, too thin an oil, or worn oil pump. However don't these engine have hydraulic valve lifters so with low oil pressure I would have expected rough running.

 

If the pressure stays above about 40psi hot then its is probably a faulty sender and that is the most likely if it is matched to the gauge. many would, as suggested, simply fit a new sender but the oil pressure quoted by the vendor look wrong to me so I feel a mechanical test gauge is the best first "test" in this case.

 

I think it is also vital to rule out a wiring fault. An electric gauge off the scale could indicate (as said by another) a chaffing cable shorting out one readng zero could indicate a broken wire or poor connection.

 

 

 

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