low oil pressure 1989 type 44 turbo

[Graham Thackrah]

Hi List,

Driving about last night and on first start up oil pressure gauge flicks
round to 5 bar as usual when cold. As it got warm though the pressure at
3k rpm was only about 3 bar. Not very normal. Oil level is fine. No
warning buzzers went off as it still just about made 2 bar by 2k rpm.
So, when cold, oil pressure hits 5 bar. When warm it struggles to 3 bar,
even when revved.

First thoughts are an oil and filter change (last done about 2.5k miles
ago, it usually has the VAG synta gold oil and Audi filter) accompanied
by a strip and clean of the pressure relief valve. Any other
suggestions? There were no preceeding symptoms.

Can a sticking pressure relief valve cause low oil pressure? What foxed
me was it does hit 5 bar when cold but as things warm up max pressure
drops to c. 3 bar. I suppose it could be the valve sticking `open' when
warm?? Does the pressure relief valve actively control max oil pressure,
or is it just there in case of a blockage somewhere to stop something
blowing?

TIA.

Graham

1989 type 44 turbo.

P.S. a check of the archives suggests the pressure relief valve rather
than a failing oil pump, particularly as I'm already running a stock oil
filter.