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Rb26 Oil Pressure Dropped

cactu5

By cactu5,
in Engines & Forced Induction

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cactu5 Enthusiast

cactu5

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Posted (edited)

Hi,

I've read some of the other posts about this (there are quite a few) but still was wondering a few things. I went to the servo after work, when the car was idling I looked at the oil pressure. It started dropping from the middle (4) down to 2. I turned the car off, put in petrol, checked the oil (good), started the car, and it was back to normal. So I drove home, normal the whole way (only 2 minute drive) got to my driveway idled and it started dropping again 3, 2, 1. I stopped the car. started it again and it just sat on nothing, the warning light didn't come on, but I didn't let it idle for long, I've heard bad stories.

It looks like it's either the sender, the oil pump, or motor's gone (unlikely running well). I was wondering how do I test easily?

Does an oil pump die that quickly?

If it's the oil pump, can I change the pump, or do I have to rebuild motor? I was told that something wears in the motor, which breaks the pump so no point in just changing the pump?

I only have about 2K at the moment, so rebuilding the motor isn't really a good option for me. Maybe T/S for me though. C'mon Santa I need some forgies :( .

Edited by cactu5
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https://www.sau.com.au/forums/topic/146111-rb26-oil-pressure-dropped/
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VSPEC-33 Community Regular

VSPEC-33

Posted
Posted

Rig up another sensor and gauge to get an independant reading. Can get one of those sandwich plates to go on the oil filter adapter, borrow/buy a gauge and get a fresh reading. Good luck mate, hope its nothing too serious.

cactu5 Enthusiast

cactu5

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  • Author
Posted (edited)

I might start it again, let it idle and see if the light comes on. It wasn't knocking or anything when I turned it off.

If there's no oil pressure, how long do you think I've got on idle before motor disintegrates?

Edited by cactu5
Beer Baron Grand Master

Beer Baron

Posted
Posted

well if there is no oil pressure the engine should last around 30 secs or so at idle. at 7000rpm it may last 3 seconds or less.

you do realise that oil pressure is not constant? it goes up and down with revs. so the lower the revs, the lower the oil pressure, that is normal. so after sitting at idle for a bit it's not uncommon for the oil pressure to be between 1 and 2 bar. when driving it should be always over 4 bar and at 3000rpm it should be nearer 6bar.

i have found my standard gauge is fairly accurate, just a touch low, but it is very slow to react.

cactu5 Enthusiast

cactu5

Posted
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I started the car. The oil pressure is beautiful again. Maybe it's the gauge, I can't see an oil pump working fine, sieze without warning, then work fine again. I'll take it to the servo, do an oil pressure check, and maybe get one of those guages like V-spec suggested.

cactu5 Enthusiast

cactu5

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well if there is no oil pressure the engine should last around 30 secs or so at idle. at 7000rpm it may last 3 seconds or less.

you do realise that oil pressure is not constant? it goes up and down with revs. so the lower the revs, the lower the oil pressure, that is normal. so after sitting at idle for a bit it's not uncommon for the oil pressure to be between 1 and 2 bar. when driving it should be always over 4 bar and at 3000rpm it should be nearer 6bar.

i have found my standard gauge is fairly accurate, just a touch low, but it is very slow to react.

I know that oil pressure gets low when idling, but it went down to zero oil pressure.

When you say the engine should last thirty seconds at idle, do you mean thirty seconds until there is a knock, or thirty seconds until I destroy it?

Beer Baron Grand Master

Beer Baron

Posted
Posted

ok another point. you also need to remember that when cold the pressure will be much higher than when at operating temp. so when you start the car in the morning when it's cold it will probably be 6 or 8 bar at idle. at operating temp it should be 1-2bar.

if your oil pump truly did fail, and you have no oil pressure at idle you'd have 30 seconds before trouble. a bearing would start to wear in about 5 second I'd guess. even at idle your car turns over 500times in 30 seconds....

djr81 Grand Master

djr81

Posted
Posted
I started the car. The oil pressure is beautiful again. Maybe it's the gauge, I can't see an oil pump working fine, sieze without warning, then work fine again. I'll take it to the servo, do an oil pressure check, and maybe get one of those guages like V-spec suggested.

The most probable answer is that the oil pressure sender unit has failed or is suffering from an intermittent failure. Mine used to randomly change pressure & despite how ever many times you tell yourself not to worry you end up getting paranoid about it. So I fitted a new unit & the problem went away. If you are going to get it checked then it is well worth pricing up a new sender unit as they aren't massively expensive. Change it out when you next change the oil.

The oil pump is directly geared/coupled to the crank so if it seizes the engine won't go round....

Beer Baron Grand Master

Beer Baron

Posted
Posted
The oil pump is directly geared/coupled to the crank so if it seizes the engine won't go round....

yeah but there plenty of other ways for it to fail!! :D backing plate coming loose is a common one and engine will still run (till it dies). shattered pump gear (sometimes engine will still run till it destroys itself). those are probably the most common type of oil pump failure on RB26s.

djr81 Grand Master

djr81

Posted
Posted
yeah but there plenty of other ways for it to fail!! :D backing plate coming loose is a common one and engine will still run (till it dies). shattered pump gear (sometimes engine will still run till it destroys itself). those are probably the most common type of oil pump failure on RB26s.

Just as there are 50 ways to leave your lover, there are many ways to kill an oil pump. I was just trying to pull him up on the seizing thing, is all.

cactu5 Enthusiast

cactu5

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The most probable answer is that the oil pressure sender unit has failed or is suffering from an intermittent failure. Mine used to randomly change pressure & despite how ever many times you tell yourself not to worry you end up getting paranoid about it. So I fitted a new unit & the problem went away. If you are going to get it checked then it is well worth pricing up a new sender unit as they aren't massively expensive. Change it out when you next change the oil.

The oil pump is directly geared/coupled to the crank so if it seizes the engine won't go round....

:P So true, it doesn't matter how many times you tell yourself.

Thanks, it is starting to sound like it is the sensor. I started the car this morning, oil pressure was great, took it down the road to mechanic. While I was cruising along the oil pressure dropped from 4 to 1.5, I freaked a bit, but it stayed there and by the time I got to the mechanic the gauge was just going all over the place. He said he'd do an oil pressure check when I take it in for a water pump issue. He seems to think it may be the sender too.

He said if the oil pressure was too low I should hear some kind of rattle, and I can't and haven't heard it. Still I wont be driving it around until this is resolved.

I'll definately price up a sender unit, thanks.

cactu5 Enthusiast

cactu5

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might not be the sender.

I drove the car up the road last night. Oil pressure was fine at that time. parked the car. Got in it again this morning, went to start it and heard the loudest grinding metal sound ever. Stopped the car immediately. WTF? Anyway, I don't know if it was the water pump throwing a bearing, because that was on its way out, or if it was the motor dying. Either way it's not going any where. FARK :P

cactu5 Enthusiast

cactu5

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I read on the forum about the guy who heard a grinding sound with his RB25 and it looks like his motor completely beyond repair. It seems strange that mine ran fine when I turned it off last night? I don't know what's going on.

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