Oil warning light

[Softy]

My old TB GQ used to do it on idle after i went with Nulon instead of Castrol for one service. The Nulon oil would thin out heaps at running temps on a warm day. Changed back to Castrol next service and never saw the oil light ever again apart from when starting it.

[Patrol'n]

Hey mate, I have a dodgy oil light in my TD42 GQ too, it has done it a few times now, the oil light will come on and stay on for a while. Both the stock gauge and my aftermarket gauge show normal oil pressure and the oil level is fine too.
Don't know why it does it.

It's very annoying when these gremlins occur, maybe when I figure mine out, it might give you a hint why yours is doing it :-)

[Patrol'n]

My old TB GQ used to do it on idle after i went with Nulon instead of Castrol for one service. The Nulon oil would thin out heaps at running temps on a warm day. Changed back to Castrol next service and never saw the oil light ever again apart from when starting it.

That's interesting, did yours still show oil pressure on the gauge too?

[Softy]

Yup used to sit just under 4? all day long with the Castrol.. With the Nulon it would sit below 2 when hot and the light would flicker. motor had about 400,000k on it at the time.

[Patrol'n]

Update time, following the info from Softy, I figured I would change the oil and filter, never a bad thing to throw some new oil in anyway, even if it didn't fix the problem :-)

Chucked in some Penrite this morning, and I've driven about 100 kms today, various speeds, idling with aircon on etc.

So far, I have not seen the light come on, so we will see how it goes over the next few days, fingers crossed!

[dom14]

Update time, following the info from Softy, I figured I would change the oil and filter, never a bad thing to throw some new oil in anyway, even if it didn't fix the problem :-)

Chucked in some Penrite this morning, and I've driven about 100 kms today, various speeds, idling with aircon on etc.

So far, I have not seen the light come on, so we will see how it goes over the next few days, fingers crossed!

Since you've already done the oil pressure test and it has passed the test, I reckon it's an electrical issue. Dodgy wire or connection somewhere.
The sender unit doubles as a oil pressure gauge sender as well as low oil pressure switch.
Low oil pressure part of the sender unit usually don't give any trouble. It's the oil pressure gauge part of it is the one that usually gives trouble and causes the dash oil pressure gauge to show low oil pressure.
If you already changed the factory oil pressure sender with a replacement one, then it may be bit faulty or loose wire or connection somewhere. The factory sender's body is the earth.
If you haven't touched or replaced the factory sender unit, may be it's worth pulling it out and testing it.
Follow my thread on repairing the factory sender to get it going without having to buy a new one.
It's fairly easy to repair it(Basically it's a cleaning job).
It's bit of a PITA to undo the sender from the engine block 'cos it's tight fit, but not too hard.
You'll need 17mm spanner, either a short handled one or a make shift curve handled one.

[Patrol'n]

Since you've already done the oil pressure test and it has passed the test, I reckon it's an electrical issue. Dodgy wire or connection somewhere.
The sender unit doubles as a oil pressure gauge sender as well as low oil pressure switch.
Low oil pressure part of the sender unit usually don't give any trouble. It's the oil pressure gauge part of it is the one that usually gives trouble and causes the dash oil pressure gauge to show low oil pressure.
If you already changed the factory oil pressure sender with a replacement one, then it may be bit faulty or loose wire or connection somewhere. The factory sender's body is the earth.
If you haven't touched or replaced the factory sender unit, may be it's worth pulling it out and testing it.
Follow my thread on repairing the factory sender to get it going without having to buy a new one.
It's fairly easy to repair it(Basically it's a cleaning job).
It's bit of a PITA to undo the sender from the engine block 'cos it's tight fit, but not too hard.
You'll need 17mm spanner, either a short handled one or a make shift curve handled one.

Thanks Dom, the factory sender was replaced about 6 months ago as it was doing exactly as you said and showing low pressure on the gauge when there was in fact plenty of pressure.

I have also replaced the earth straps with fresh and added a new one for good measure, but was still thinking a dodgy connection or wire somewhere.

If the light plays up again, which I'm hoping it won't, (but guessing it will), I'll have a check of the wires and see what I can find. Failing that, might have to replace the sender with an OEM one and see if that fixes it.

[dom14]

Thanks Dom, the factory sender was replaced about 6 months ago as it was doing exactly as you said and showing low pressure on the gauge when there was in fact plenty of pressure.

I have also replaced the earth straps with fresh and added a new one for good measure, but was still thinking a dodgy connection or wire somewhere.

If the light plays up again, which I'm hoping it won't, (but guessing it will), I'll have a check of the wires and see what I can find. Failing that, might have to replace the sender with an OEM one and see if that fixes it.

You've already replaced the factory sender unit. It must have cost you around $130 to do that.
If you suspect the unit is faulty, pull it out and test it. You can either hook it up and use air pressure gun or measure the resistance readings without hooking it up. Both tests need air pressure gun. Might be better if you use piece of matching rubber hose to connect the sender and the air gun. Check the dashboard oil pressure warning light and the pressure gauge dial while applying the pressure to the sender unit. If the sender is faulty, you shouldn't have to buy another one. It should be replaced under warranty by the place you bought it from. If the sender is not faulty, then you have an electrical connection issue somewhere. It can be PITA to locate it, but you need to do it, 'cos oil pressure warning light is important that it works without any hiccups, unless of course you have an aftermarket low oil pressure warning system installed(which is something I'm about to do atm)


P.S. Just remember when you test the Oil Pressure Sender Unit, the body of the unit is the earth. So, you need to wrap a wire around the sender unit & earth it to get it to work off the engine block.
From memory, the black wire is for the Low Oil Pressure Warning dashboard light. The Yellow wire is for dashboard oil pressure gauge. Those colours are from the factory sender unit. OEM or aftermarket compatible replacement sender units may have different colour wires.
The colours of wires coming form the wire harness is different to the above. Check my thread, I documented all that detail in there.

It's not impossible the two wires to get mixed up and wire incorrectly, though not likely if the replacement sender unit has the same plug(or socket) as the original factory one.

BTW, you might need a fair bit pressure to test the sender unit off the engine block as above. Lets say above 50psi or so. Ignition on and the sender unit off the block, the oil warning light should be on. As you apply the pressure to the sender unit, check the pressure reading on the air gun or compressor pressure gauge, and check to see the dashboard warning light goes off or not or whether it's flickering, etc.

[Softy]

Update time, following the info from Softy, I figured I would change the oil and filter, never a bad thing to throw some new oil in anyway, even if it didn't fix the problem :-)

Chucked in some Penrite this morning, and I've driven about 100 kms today, various speeds, idling with aircon on etc.

So far, I have not seen the light come on, so we will see how it goes over the next few days, fingers crossed!

Good to hear it has seemed to have sorted the problem out... Gotta love an easy fix!