Low oil pressure warning

[blackrose]

I just came back to my mooring after giving the engine a bit of a workout up the river and as I gradually reduced the revs from around 2000rpm to about 600rpm the low oil pressure warning alarm sounded. I think it's the same alarm that signals engine overheating and when I snapped a fanbelt once it sounded a constant tone, but this time the alarm was an intermittent beep.

 

I switched the engine off as soon as I could and when I checked underneath expecting to see oil all over the engine hole, everything was fine. Plenty of oil on the dipstick, no signs iof any leaks.

 

Does anyone know what's going on here?

 

(Isuzu 55 with full instrument panel)

Edited September 9, 2012 by blackrose

[Harmony]

First thing is check the tension on the belt and make sure the belt has a good grip on the pully's. I have fitted an oil pressure gauge and an oil temp gauge both these instruments are in my opinion are invaluable as they give you up to the minute engine info and can be fitted easily.

Edited September 9, 2012 by Harmony

[blackrose]

The instrument panel has an oil temp gauge and pressure gauge. The pressure gauge was fine while I was giving the engine some welly, but as soon as I went to idling the gauge showed low pressure and the alarm sounded. When I put the gearbox into neutral the alarm stopped. I will check the belts.

[bottle]

Probably just one of those things.

 

If the oil pressure returned to normal at tick over and at cruising rpm, I would just keep an eye on it for the next trip.

[bizzard]

The instrument panel has an oil temp gauge and pressure gauge. The pressure gauge was fine while I was giving the engine some welly, but as soon as I went to idling the gauge showed low pressure and the alarm sounded. When I put the gearbox into neutral the alarm stopped. I will check the belts.

If the belts and everything else are ok including gauge, sender, cooling system ect i'd say your oil is getting too hot, thinning too much and so reducing the oil pressure. You may need an oil cooler, or a higher viscosity sae spec oil, if you use 10/40 oil try 15/40, thicker, or it might foam and you could loose pressure entirely.

 

Used to get foaming with the air cooled VW cars and vans with engines at the rear shielded from the cooling wind slipstream,although they had an air cooled oil cooler, if someone had put too lighter multigrade oil in them, we always cured it by using straight oils, sae 20 in winter and 30 in summer. Mind you these of course were much older engines than yours.

 

PS Could be pressure relief valve sticking slightly off its seat by dirty oil on tick over but i doubt it knowing how you care for things and i expect your oil is change regularly.

Edited September 9, 2012 by bizzard

[Grace and Favour]

We've a Beta engine (& instrument panel)

 

Yesterday the alarm buzzer let rip - continuously - worryingly - incessantly - damnit!

 

After much investigation, exploration, head-scratchin' and discussion - - - we realised what the problem is..........

 

 

A faulty buzzer !

 

b'stard!

[MoominPapa]

The instrument panel has an oil temp gauge and pressure gauge. The pressure gauge was fine while I was giving the engine some welly, but as soon as I went to idling the gauge showed low pressure and the alarm sounded. When I put the gearbox into neutral the alarm stopped. I will check the belts.

You're being a tease and not telling us what the actual pressures are/were. Oil pressure warning systems walk a tightrope between being sensitive to real failures when the engine is runing at high RPM and not giving false errors at idle with hot oil and a bit of wear in the engine.

 

If the pressure at idle is only just dropping enough to trigger the warning, and only when the engine is hot (but not overheated), it's fine. If the pressure is substantially low, and the pressure at running rpm is down too, there's likely a problem. Check for overheating, and a diesel leak that's diluting the oil. Failing that damage to the pressure relief valve or wear in the oil pump and bearings are possibilities.

 

MP.

[alan_fincher]

Failing that damage to the pressure relief valve or wear in the oil pump and bearings are possibilities.

I know not a lot about Isuzus, but if the reduction in pressure has occurred quite quickly, without warning, and both the warning and a gauge seem to be saying the same thing, based on my experienced of other engines, the oil pressure bypass is a strong contender.

 

As well as getting stuck partially open being a possibility, we have once had one on an old Perkins engine where the spring broke, leaving it effectively fully open. Not maybe that equivalent to an Isuzu, but after that, it wouldn't make more than about 20 psi at normal operating speed, when 50 or 60 psi would have been normal without the damage.

[Justme]

You may need a higher viscosity sae spec oil, if you use 10/40 oil try 15/40, thicker,

 

 

 

Changing to a 15/40 will not help when the engine is warm. The first number is the cold thickness & the second the hot. So upping to a 15/40 will make cold starting harder as the oil is thicker & cause more wear but not affect warm/hot running as the 40 grade is the same.

[gazza]

Agree with the above.

[Serenity Malc]

Yello,

 

It'd be worth checking the oil level when cold and making any adjustments then .... failing that, unless you've recently serviced the motor I'd give it an oil and filter change.It's so easy with a pump out sump.

 

It was a hot day yesterday when you came past .. and older oil does lose it's viscocity over time.

 

Malc.

[pistnbroke]

KISS change the oil pressure switch and check the idle speed is not below that recomended.Only a mechanical /capilary type gauge will tell you the true oil pressure.

Edited September 10, 2012 by pistnbroke

[Serenity Malc]

Yello,

 

Yeah ... what he said.

 

My idle speed on a Barrus Shire 35 is about 900 rpm when cold. Even on your bigger motor it might be worth slightly raising the idle from 600 to see if than cures the problem.

 

Also you say that the buzzer shut off when you took the boat out of gear at dead slow. This may have simply unloaded the motor from dead slow in gear to allow the revs to rise just enough to shut off the oil pressure buzzer.

 

Just an idle thought !

 

 

Malc.

Edited September 11, 2012 by Serenity Malc

[billS]

Changing to a 15/40 will not help when the engine is warm. The first number is the cold thickness & the second the hot. So upping to a 15/40 will make cold starting harder as the oil is thicker & cause more wear but not affect warm/hot running as the 40 grade is the same.

 

I believed that to be true - until I changed the 15/40 oil in my Beta 1903 for Morris Golden Film 10/40. The oil pressure at tick over was definately lower at operating temperature, with the result that the buzzer would sometimes sound - especially on throttling back to tickover after prolonged running at high revs on the river. The problem disappeared when I reverted to 15/40.

Edited September 11, 2012 by billS

[DHutch]

...i'd say your oil is getting too hot, thinning too much and so reducing the oil pressure...

This what the first thing I thought after I read that you have been giving it a good leg stretch down the river, but I agree it could also be a stuck relief valve.

 

I think my first post of call would to fire it back up now its cool and see how it behaves now.

And as said, see what the 'low pressure' actually is and if its really not or just below the threshold.

 

Loss of oil pressure is a serious matter in terms of engine life, and I would always advise turning the engine off as soon as possible (ie, instantly, if you anywhere but over the mouth of a weir) if your unsure, but equally once you know more and if its only just under it might not be something to worry a great deal about.

 

 

Daniel