Oil pressure question

[Matt No VAT]

Can anyone confiirm what the oil pressure should be on a Alfa V6 3 litre unit?

Ideally I need to know what the pressure should be on start up, then what the pressure should be once the engine is up to running tempreture.

I don't think I have a problem but just wanted to see what other people's cars were running at.

Thanks in advance.

[Bob]

Hi Matt,
mine is just over 40 on the gauge when cold and goes to the same when warm and reving high enough(!), however it does drop right off (below 10)when ticking over when hot. It's been the same since I bought it and other than putting a refreshed bottom end in it I'll just live with it. It does seem healthy enough anyway!.

[Matt No VAT]

Bob, Many thanks maybe I do have a problem then...

I'm hitting just under 100 psi when cold which I think is approx 7.5 bar!

It's not a high pressure pump as far as I'm aware, so I'll have to have a little look around and see whats up - maybe its the guage...

oh how I love electrics... not!

[Bob]

Does it stay at that or drop when warmed up?. Having said that you probably don't want to leave it running to find out!.

[Matt No VAT]

Yes, it drops off to about 80/85 which makes me wonder if its either the guage or the oil pressure sender. Sender was new though, as is the oil and the filter.

[David May]

My 24V shows 8bar cold and drops to just under 5bar when really hot. Watch those Veglia oil pressure transmitters - I've had two go faulty (usually start to read very low then leak!) - they appear to be very sensitive to vibrations at high revs. Mine is now on a flexible pipe and seems to be holding out.

[rutthenut]

Agreed with Dave May on this - the oil pressure senders on the Alfa V6 is frequently known to fail. But as far as I know it will read lower than actual pressure when it does.

I do depend on the low oil pressure switch/lamp at tickover, rather than the low reading on the gauge, and that doesn't seem to some on if the engine is running.

As you have a new item, and you are worried about over-pressure, then I don't think that will be the problem in this case.

So I would suspect that gauge may be slightly off from the pressure sender?

J.R.

[Matt No VAT]

John,

I think your right that its actually the sender and the guage being out of sync.

It does not seem to be blowing oil out anywhere (other than the gearbox output shaft, which is awaiting the new seals and repair kit on Thursday).

Thanks for you input all,

[Arthur]

Guys,

My 12-valve runs around 5 Bar (75psi) cold at idle and and some revs.
Drops to around 4 Bar when hot and at running speed - shows 1 bar or less (25 lb switch flashing permanently) at idle.
When really hot (track days) - almost sod-all at idle.
Picks up from there to around 4 bar at around 3000 revs, but proportionately less as the revs fall.
Doesn't seem to worry it any.

But watch your oil grade as well - synthetics are effectively thinner when cold and won't show so much pressure. Shouldn't be much difference when revving, and controlled by the relief valve.

Remember also that oil is only a lubricant for a small part of it's time - it's main job is as a coolant. If your pump is pumping thinner oil, pressure is lower, but flow is higher, so you get better cooling. Most of the bearing pressure comes from hydrodynamic wedge, arising from the rotation of the shaft in the bearings, provided there is oil present. The Alpha has under-piston oil jets as well, for cooling, and while these need pressure to work, it isn't a problem at speed when the pressure is good, and there isn't the heat to shift at low speed or idle, so again, no problem.

I did have one worry - with very low pressure (like when hammering the engine), I got a nasty knock at idle, disappearing as I put some revs on. I worried some about this. Finally turned out to be an iffy plug - knocking disappeared with a good set, and it's a damn site cheaper than a rebuild. I also had the injectors checked - but again, the Bosch guy reckoned they'd have to be utterly shot to be a problem, so OK there as well.

Oh yes, when I first installed the engine, it idled at around 600 revs. Not enough to charge the battery at idle was a problem - but I managed to raise this to 800 rpm by tweaking the throttle stops and potentiometer, and it also picked up the idle oil pressure somewhat as well. May be possible to lift it further if your heart really can't stand looking at a pressure needle sitting on the backstop.

Hope this is some help (or comfort, at least...)