the taxi ive got now is a 52, 2.2DTi vectra, but the thing is the oil pressure when driving drops really low, then will go really high then sit normal for a bit and high, normal, low etc etc. and im driving it to get the best mpg i can, but the computer says im getting 34 mpg!!! im no expert but surely theres something wrong in that? its crying out for a service every time i start the car, the guys i rent it off say thats normal! i dont really care if the cars fucked coz if it breaks i dont pay, but where the mpg's are concerned i am

thoughts?

A good service will help towards better MPG.

Knackered oil maybe the cause of those fluctuations you talk of, as when oil is buggered it gets thinner therefore pressure will drop.

I'm with Ste, an oil and filter change will do wonders for your economy and oil pressure, especially with a diesel.

It's perfectly normal for oil to fluctuate to a certain extent though, cold oil is thicker than hot oil, so you'll probably get a little bit more pressure on cold start than at other times, and when you sit in traffic, the engine gets hotter, the oil gets hotter, and thins out a tad causing a small pressure drop.

Get that oil changed though, if the economy is suffering it's because the oil is breaking down and allowing to many parasitic losses in the engine. The crank, cams, piston rings and valve stems will all be sapping power due to friction building up.