Oil pressure decrease

[Mezzell]

So I’ve looked back in the forum and found a few posts on this topic but would appreciate it if anyone could shed any light on my situation.
The last couple of times I’ve driven the car (CV8 5.7 heavily tuned) I’ve noticed a drop in oil pressure. Used to be about 3 bar on tick over when started cold which would drop to about 2 when warm. When driving it would be up between 3-4 bar.
Recently it’s dropped to as low as .5 bar on tick over when warm but still goes up to around 2 when driving.
The oil was fresh when I bought the car (around 2500 miles ago).
As the gauge as indicated a drop in pressure across the board I’m guessing it’s not a sensor and am worried that it could be the pump.
Would it make sense to change the oil and filter first and see what happens?
Does the oil have to be drained to change the pump?
Any help would be greatly appreciated.
Thanks in advance!

[leigh1050]

It might sound daft but have you checked the oil level?

[Boosted LS1]

I can't see it being the pump and I'd be surprised if the 'O' ring seal has deteriorated although it's a possibility I guess. You can take a pressure reading immediately after the pump.

Is it an ls2 engine? Sometimes a cam bearing may walk which causes a loss in pressure. It could also be wear on the shells. Maybe you could send an oil sample off for analysis?

The first thing I'd do is a check with new oil.

[Mezzell]

The oil level is spot on. I’ve only had to put in about 250ml in 2500 miles and it does get driven hard.
It’s an ls1 block with ls2 heads.
I think I’ll change the oil and filter and report back. Just worrying the way it seems to have happened so quickly. I’d understand the oil deteriorating over time and seeing a slight pressure drop......... the cars only done 50k.

[throwyourbike]

That does seem alarmingly low.

My LS2 sits at 3 bar on cold idle. I don’t think I’ve ever seen it drop below 2 bar, even stuck in traffic at the height of summer.

I would refrain from driving it. As you say, change the oil and see if that makes any difference.

[vxr2010]

is it worth changing the sensor , as they are prone to failure , i don’t think they are much £ , walkinsaw or Aas in newcastle or abroad Rock auto via fed ex as then what you pay is landed all inclusive cost , ive not had to change mine , but i think it’s on the back of the block need a certain size socket to do it

[mfp4073]

I can't see the correct spec oil degrading that much if at all in 2500 miles of road use. Check the oil colour and consistency via the dip stick first, My money is on the oil pressure sensor as they are prone to failure.
I would also listen out for any tapping/ knocking or rumbling noises from the engine when it's hot.

[Mezzell]

I really hope it is just a sensor!
The oil looks normal, the cars behaving normally (although I obviously have only driven it very gently since this issue started) and there’s no untoward noises coming from anywhere.
I think I’ll replace the sensor before I do anything else.

[maccavvy]

Sensors are known to go ..usually either nothing or top stop.
I'd deffo change the oil to check..
And the sensor next.
What grade oil are you using

[vxr2010]

i noticed on the ls3 after putting a 10/40 in rather than the standard 5/30 that the oil pressure ran higher , the monaro i always use a 10/40 i think the 5/30 is too thin , but i’m still thinking oil sensor is the most likely cause of your issues

[Mezzell]

I don’t know what oil was in it when I bought it but having only topped up by 250ml and not having any issues up until now I would think it’s not the oil itself. I will change it though and will order a sensor tomorrow and hopefully this will sort it.
I’ll let you know the outcome........thanks for the replies. It’s appreciated.

[Lincsls1]

It'll just be the sensor. There is nothing else going on to suggest otherwise. And its such a common issue on so many other cars too, sensor failure.
Worry not!

[Mezzell]

So, quick update.......
Changed the sensor, no difference.
Changed the oil and filter, no difference.
Checked the wiring both ends of the gauge, no difference.
The weird thing is, when the engine gets warm and the gauge reads 0.5 bar of pressure, the needle then starts pinging around from 0 right up to maximum......
Could I have a faulty gauge?
I know this is probably the least of anyone’s worries at the moment but any help would be greatly appreciated.

[Lincsls1]

I'd say yes it is perfectly possible for the gauge to be faulty even if intermittently. Why not at the end of the day?
I can tell you that the voltage gauge was faulty on my 5.7VXR. It would read perfectly until the car had running for a while and then the gauge would just drop to zero. A quick tap and it would return to normal, but would also read low voltage, again until tapped.
I have since swapped my gauge and its be fine ever since.

[Lincsls1]

Is your car a facelift CV8 or a big boot CV8 with retro fitted gauges?
I'm just wondering if there are 2 oil pressure senders, one for the ECU and one that solely drives the gauge.
I believe that is the case for my 5.7VXR since the gauges where fitted by HSV unlike the gauges on the LS2 VXR and later CV8.

[Mezzell]

It’s a big boot CV8 so the gauges have been retro fitted.
Is there a low oil pressure light on the dashboard?

[Lincsls1]

Mezzell said:

It’s a big boot CV8 so the gauges have been retro fitted.
Is there a low oil pressure light on the dashboard?

Ah right. Then I would suggest someone has perhaps installed a second oil pressure sender which is just for the dash gauge a bit like I'm thinking my 5.7VXR has. That would make more sense as to the erratic behaviour of the gauge.
I don't think there is a low pressure light as such, more that the digital display on the speedo will display an appropriate warning.

[Lincsls1]

I've done a bit of quick searching and it seems I'm right, there is no oil pressure light, but an oil warning message will be displayed on the speedo.
I bet you have a second sender and it is this that is causing your gauge to flip out!

[Mezzell]

Thanks for that.
I will have to see if I can get some info off the sender tomorrow and try and locate a new one.

[motomk]

At one stage I had some gauges to fit to a VYII SV8 Commodore (Commodore equivalent to the big boot Monaro sent to the UK, V2 series 3)
Now I did sell them a long time ago but not before I took pictures of the fitting instructions. If you want a copy, drop me an email. The sender was a VDO unit. Have a picture of it but not any numbers or anything.
I seem to remember the early way of doing it was a sender near the oil filter. On the VZ cars it could read it from the computer.