Any ideas how much it should cost to replace the oil pump?

A lot since you have got to lift the engine out or drop the crossmember and sump!

 

If you have low oil pressure it is probably the sender unit which is at fault!

 

Mark

Pretty certain it's not the sender since the sender is onlt a couple of months old and has always behaved the same as the previous one.

 

There appears to be some kind of pressure regulator in the oil circuit. Was wondering if it was that.

 

Odd behavoiur is that pressure seems fine until the first time I boot it.

Before you start pulling it apart get a garage to test the pressure with a proper mechanical gauge.

What exactly is it doing then?

Once fully warmed up, if I take it easy on the motorway with the revs at 3000 it stays constant at just below 60 psi. If I have to have her idling for any reason it's at about 30 psi and stopping the engine/restarting after a couple of minutes stoppedshe idels at 30 psi.

 

Put one floor it and the turbos have kicked in, she can be as low as 45 psi at 3000 with the idle between 20-25 psi. Stopping/restarting and the idle is only just over 15 psi.

 

Wait several hours and all is back to normal.

 

Only other issue that she's going through over a litre of oil every 1000 mile which probably isn't good but I suppose should be expected for 180k miles

sounds like my Jap NA. Cruise and the oil pressure's just above half way on the dial (not in psi cos it's Jap). When it's cold it reads high, but if i give it a bit then it falls to below one quarter when you slow down again, but comes back up to half way after a while.

 

I'd got it down to the oil being pumped at different rates to different parts of the engine at different revs - so the oil pressure reader is only reading what's happening where it's located, not in other parts of the engine.

 

Some times it falls to almost zero - long left hand deceleration bends are a favourite ie coming off a motorway.

 

But the car's fine - dosen't use any oil, no leaks and runs really sweet - so I use the oil gauge as a source of entertainment...

 

good luck

 

Jack

That sounds pretty much normal to me. All that is happening is that the oil is warming up and getting thinner, it then passes through the orrifices in the engine easier so there is less pressure there - simple really ;)

 

CheerZ,

 

Andy

My main convern is that it never used to do. Seemed to start behaving like this a few months after I had a cylinder head replaced. Sure as hell had never seen her idling below 25 psi until then although I suppose that it gould be better (hopefully :)) grades of motor oil

Andy

 

...thanks for the answer - I normally manage to get my head around such mechanical happenings but this one was loosing me. Must have been over complicating things ...it's obvious when it's pointed out.

 

...thanks again.

Thanks Andy

 

I understand the hydraulics. But why a pressure drop just because I've booted it. I suppose the extra heat from Turbos might change the properties, but that much?

 

For my peace of mind, how does the pressure regulator work?

The pressure regulator is just a ball bearing on a spring with the ball sitting snuggly in a seat. The ball lifts of the seat and lets too high pressure bleed away back to the sump. This is preferable to seals popping out! If you take the oil filter off you can see this ball (I think - not sure now if its not my other car) and push it off the seat even to check it isnt stuck open a little with some debris and causing a pressure leak. It doesnt go wrong normally. The zed also has a spring loaded valve that diverts some oil to the oil cooler when above a certain pressure - about 50psi I think. So that when you are working it really hard the max is going to the cooler. But at low rpm nothing goes to the cooler to keep the low pressure actually shoving oil round the engine.

 

To re assure yourself just take off the oil filler cap when idling hot and you should see floods of oil over the camshaft lobes.

 

You got to get used to these electric guages not being very reliable. A low pressure warning light would be better imho. At least you'd notice something wrong with it