Jackaroo - Oil Pressure Gauge

Dear WDR, gauges and warning lights are there for a reason.

Sometimes they develop a fault which gives a "false" reading, but not often. In your case it sounds like your engine has a serious fault that cannot be ignored. I would advise you not to drive your vehicle or even start the engine until a mechanic has had an inspection. Rus.

Geez, talk about doomsday pessimist!

WDR,
Gauges and sender units quite often play up more times than the oil pump, another thing you should consider is the oil itself, oil thins out as it gets warmer, as your gauge is reading ok when cold and drops as it gets warmer I would be checking what oil was used at the last change, ( it has been changed in the last 10-15 thousand I presume ? ) and make sure the oil weight ( the 20-50 bit ) is within specs for where you live, ask a good local mechanic.
I would also recomend going to the same GOOD local mechanic to suss the problem out further if need be, and not the holden dealer, do a search on this site on 'Holden', 'Toyota', 'Nissan' and other dealerships to see what they get up to with what starts of as a 'minor' problem.
If you don't know of any local mechs you can trust let us know your location and there's a good chance some-one here will know one they can recomend nearby.

Avagoodn
Pezza

Had exactly the same happen to my previous 1997 3.2 V6 Jackaroo at 73000kms. Problem was the oil pressure sensor (only). Cost me $263.45 for Holden Dealer to fix (with 2 yr. warranty). I also found that 4WD driving slowly (low revs) in hot conditions the oil pressure looks a bit low. Part of the problem was that with THAT motor (unk. re. 3.5) Isuzu reccomend 20w50 and the Holden dealer kept putting 20w40 in. With 20w50 pressure was marginally better. Good luck.

Personally, I would lean more towards the sender unit as faulty. Also check the book and make sure the correct oil is used. VERY IMPORTANT these days.
There is a HUGE difference between NIL and almost nil, Nil will activate the dash warning light (if working). If that came on switch the engine off immidiately. Also engine noise would increase heaps and you will notice the difference.

From expierence, I wouldnt take it to a dealer either, I would find myself a local mechanic who has been established for a few years in the same workshop, its a good indication he is a survivor in these hard times for mechanics to make a living.

Look for things like workshop cleanliness and not a one man shop. Most mechanics will check the pressure for you while you wait (after you make an appointment for them to check it, Its a fairly quick check to do. and the advantage is, if he is genuine, he will allow you to observe things as he works on it and that way you can see he isnt going to make things worse than what they really are. Believe me, some mechanics will do that to make the repair worth while for their pockets.

I am sure you have some good workshops local up your way, just have to find one you feel comfortable with. Dont panic just yet, todays engines are well designed and although most manufacturers have some problems ( except early 3ltrdiesel nissans), its very rare its a major thing unless the engine has not been services at proper intervals.

Hardest part is finding one, once you do, its nice to know you can trust him.
Ange

Thanks everyone for your help - The car is now quarantined until I can get to the dealer on Monday.
The gauge is not on nil, just near it.
The car has always been serviced in accordance with book but after travelling 150,000K at around 35,000 pa it only travelled 3000K for the last couple of years. Wife is using it.
Serviced a couple of weeks ago by GM dealer
God only knows what oil they put into it.
The dreaded 160,000 service ($1500 plus) is around the corner so I will keep everything crossed with this/The joys of retirement.

Again my thanks to all

WDR,
At about 100,000Km, 3 years ago, our '97 3.2L Jackaroo had a problem with its oil pressure gauge, wandering all over the place, then reading normal for a while, then misbehaving again. I eventually replaced it. The cost was $160 then, and non-genuine units are not available.

Your engine is a 3.5L, but the sender unit should be the same, or very similar.

The oil recommended for our engine by the Manufacturer is 20W50.
We are currently using Castrol GTX3, which is 15W40.

The Oil Pressure, when the engine is at normal operating temperature, is 300 Kpa at idle and 580 Kpa when above 2,800 rpm.
When the engine is cold, the pressure is 600 Kpa when above 2,800 rpm.

The Isuzu Workshop Manual for Holden Jackaroos from 1992 on states that oil pressure should be 350 – 550 Kpa (51 – 80 psi) at 3,000 rpm.

The best method of checking engine oil pressure is to unscrew the Pressure Gauge Sender Unit and temporarily replace it with a pressure gauge. Naturally the engine should be stopped while changing the Sender Unit. Less than half a cup of oil will run out while the changeover is occurring.

If the accuracy of the dash mounted Oil Pressure Gauge is in question, its electrical circuit can be checked.

Disconnect the wire to the Sender Unit, then turn the ignition on.
If the Oil Pressure Gauge indication changes, the Sender Unit is probably faulty.
If it does not change, the fault is in the Gauge itself or in the wiring.

Check for voltage at the wire to the Sender Unit. It should be about 9 – 12 volts.

The Sender Unit resistance varies depending on the actual engine oil pressure.
The Workshop Manual gives the following values:

0 Kpa 19¿
50 26.6
200 49
400 80
600 110

These values can be used to check the accuracy of the gauge indication.
Buy a 200¿ potentiometer (variable resistor) from Dick Smiths or Tandy’s and solder two pieces of wire to its terminals. (The wires on the one I made are about 2M long, so I can sit in the car and watch the gauge while I adjust the resistance.) Connect alligator clips to the wires. Clip one of these to the Sender Unit wire and the other to any handy earth point.

Turn the ignition on, adjust the resistance and look at the Oil Pressure Gauge on the dashboard. The gauge reading SHOULD show the pressure readings that correspond with the Sender Unit resistances.

Our ’97 Jackaroo did not line up with these figures, although the indication did change with the adjustment of the potentiometer. The gauge read 600 Kpa when the resistance was 53¿.

The Oil Pressure Switch can also be checked.
Turn the ignition off and unplug the switch wire. Check that the switch terminal is at earth potential.
Start the engine. Check that the switch is now open circuit.
Touch the wire to earth while the ignition is turned on. The Oil Pressure light should illuminate.

Hope this helps,
Trev