HELP ! Low Oil Pressure BMW 540

[mike888]

I have a 96N 540i which has an oil pressure warning on tick over. Once the car gets to 850rpm the light goes out. The level is fine and the oil is fresh. The oil preesure switch is new and has just been fitted. Any ideas on what's wrong and how to fix it ?

[Mikey G]

Get a gauge fitted into the engine and see what the actual pressure is first. Could be a number of things ranging from oil pump worn, oil pressure relief valve sticking or worn, or god forbid bottom end bearings worn.
Once you get a proper gauge inline you can see what is actually happening and it may give you more idea.

[mike888]

Thanks, we have checked the pressure with a gauge and all seems well. Very strange, me thinks it must be the pressure valve. Will check it out and inform all on results.

[annodomini2]

I am probably wrong but 850rpm should be about right for idle speed, if its idling less, isn't it just that the idle is set too low??

[Mikey G]

annodomini2 said:

I am probably wrong but 850rpm should be about right for idle speed, if its idling less, isn't it just that the idle is set too low??

For a small engine yes but for a V8 i would have thought ~750rpm would be normal. Best to check on that though.

What about when the engine is cold? Is the problem there then or only when warm?

[mike888]

The problem only occurs when the engine is hot. I have turned up the idle and there does not seem to be a problem any more. I have also drained out the 5w 40 oil in favour of the good old 15/40. I am hoping this will be fine now but.......... I took it to BMW (main agent) and they now think that it needs a new block - I can't believe a car of this age and miles (95k) should need that. I figure it is just a little worn . What does do you think ? Does anyone remember mini's doing this in the 70's ?

[Mikey G]

mike888 said:

Does anyone remember mini's doing this in the 70's ?

My mini did this in the 90's (about every 2 months )

How long have you had the car? what is the service history like? I agree that these days 95k isnt a lot but if its been badly looked after 95k could cause problems.

I would seriously consider taking it to a specialist rather than a main dealer, loads about if you look. I am still putting money on the fact it could be the oil pressure relief valve sticking open slightly. Dont know where it is on that engine but it is probably built into the oil pump which will more than likely mean a major strip down anyway.

Hope you sort it.

[Globulator]

mike888 said:

I took it to BMW (main agent) and they now think that it needs a new block - I can't believe a car of this age and miles (95k) should need that.

BMW V8s only need new blocks if they blow huge amounts of blue smoke as the nikasil liner breaks down.
The liner has no effect on oil pressure.
If yours is not smoking then choose a different garage. Seriously!

The first thing I'd do is fit a new filter, the old one could be blocked with sludge and/or additives - the filter bypass relies on pressure. The second thing is find a good specialist who knows the first thing about engines, perhaps unlike the dealer?

[mike888]

Thanks for the advice. Sounds like the main dealer is just "fitting" instead of "fixing" again !

[CombeMarshal]

mike888 said:

Thanks for the advice. Sounds like the main dealer is just "fitting" instead of "fixing" again !

Thats the way its done these days!!!