Isuzu Engine Sticky Oil Pressure Switch

[Guest]

I don't claim to know anything about Isuzu engines, but posting this as it might just help somebody, sometime. 
We recently came a cross a very pleasant guy who's Isuzu engine (model unknown) was showing an oil pressure warning light and sounding the alarm. Oil level was good but last oil change unknown (he had only recently taken ownership and it was his first outing.) The engine sounded fine.
Cut a long story short, an RCR guy attended who was very on the ball, changed the oil and filter which showed improvement (now intermittent fault) but no cigar.
He then said he had attended a couple of Isuzu where the oil pressure switch had stuck, and upon changing this normal service was resumed. Naturally the owner was very pleased that a part costing a few quid had put things right. I would carry a spare one after that, since I have found that if you carry a spare, the original part rarely fails!
 

Edited July 11, 2019 by Guest

[Tony Brooks]

In my experience the majority of times a low oil pressure reading, lamp or buzzer shows on any engine it is the sender that is at fault. You would soon know by the engine noise if it was really low oil pressure. Ditto temperature readings PROVIDED the boat has been used in a similar fashion before and has shown no signs of overheating.

[Guest]

10 minutes ago, Tony Brooks said:

In my experience the majority of times a low oil pressure reading, lamp or buzzer shows on any engine it is the sender that is at fault. You would soon know by the engine noise if it was really low oil pressure. Ditto temperature readings PROVIDED the boat has been used in a similar fashion before and has shown no signs of overheating.

Certainly one that I will remember! (I had a car many moons ago where a hydraulic brake light switch had stuck, so I suppose this is a similar thing.)
Perhaps it is a good argument for a pressure gauge and a warning light! Belt and braces.

[Tony Brooks]

54 minutes ago, catweasel said:

Certainly one that I will remember! (I had a car many moons ago where a hydraulic brake light switch had stuck, so I suppose this is a similar thing.)
Perhaps it is a good argument for a pressure gauge and a warning light! Belt and braces.

But not if the gauge is electrical, their senders are just as unreliable but at least the will not dump all the oil into the bilge if a pipe fails - even if they do start to leak a bit.

[Nightwatch]

I have an electrical fault on our Shire oil pressure gauge. Anything above idle and the needle shoots up to maximum. Decrease revs slightly and it flicks about. Idle and it goes to normal. 

 

Any fix ideas please?

[Boater Sam]

15 minutes ago, Nightwatch said:

I have an electrical fault on our Shire oil pressure gauge. Anything above idle and the needle shoots up to maximum. Decrease revs slightly and it flicks about. Idle and it goes to normal. 

 

Any fix ideas please?

A short to ground anywhere on the lead between the sender and the gauge will do this.

Disconnect the wire at the sender, with the engine running, if it still does it, you have a short. If it clears the full reading its the sender that is duff. Shorting the wire to the engine block should give you a full scale reading, no connection should give a zero reading with the ignition on.

[Nightwatch]

4 minutes ago, Boater Sam said:

A short to ground anywhere on the lead between the sender and the gauge will do this.

Disconnect the wire at the sender, with the engine running, if it still does it, you have a short. If it clears the full reading its the sender that is duff. Shorting the wire to the engine block should give you a full scale reading, no connection should give a zero reading with the ignition on.

Thank you. I will have a fumble.

[Boater Sam]

You're welcome, its most likely the sender, its a rheostat usually that the pressure alters the resistance of, contains moving parts so things wear.

[Kudzucraft]

5 hours ago, catweasel said:

Perhaps it is a good argument for a pressure gauge and a warning light! Belt and braces.

Yup. I am petrol head and I really like to put a mechanical pressure switch on the engine in addition to the one in the car.  You can double check the readings and it is reassuring to be working on the motor and see the oil pressure while you are tuning.  I added a fuel pressure gage in the engine bay for the same reason. You can sometimes see a probably starting before you feel it driving.

[Tony Brooks]

3 hours ago, Boater Sam said:

A short to ground anywhere on the lead between the sender and the gauge will do this.

Disconnect the wire at the sender, with the engine running, if it still does it, you have a short. If it clears the full reading its the sender that is duff. Shorting the wire to the engine block should give you a full scale reading, no connection should give a zero reading with the ignition on.

An open circuit negative on the gauge will also give full scale deflection on bi-coil gauges as most boat ones are..

Edited July 11, 2019 by Tony Brooks