ebs

I have a '84 928 (US spec 4.7L engine) with around 60,000 miles on it. After a recent oil change (I have used Castrol Magnatec 10w/40 for the last several oil changes) I have noticed that the oil pressure is a bit lower. At start up, its always registered just over 5 bar on the guage, and used to get down to 3 bar at idle on a hot day. Lately its been getting down to 2 bar at idle on a hot day. Pressure also seems to be getting lower sooner than it used to. At one time it would be like 25 to 30 minutes to get to 3 bar, now its there after 10 to 15 minutes. It sits around 4 bar when hot and the engine is revved above 2000 rpm. The water temp has remained normal throughout this.

The only thing thats changed is my mechanic over filled the oil, by an estimated half a liter/quart - but I dont think that would have an impact on oil pressure, would it?

Is this cause for concern? Whats healthy/normal oil pressure for an engine on a hot day?

Sorry for the long post.
Many thanks
Ebs

hinchcliffe

I remember hearing that the thinner oils would idle at lower pressures.

Not sure why yours would be different if its been the same oil as usual.

Any leaks, noises?

AJK

Mine has done about the same thing and I also wonder if there's a problem. Currently running 10W-40 whereas previously used 20W50.

IcemanG17

One thing to consider is the ambient temp...isn't this summer for you?

ErnestSw

The gauges are notoriously inaccurate. It's more likely to be a gauge issue than an actual oil pressure change.

Bill Ball

First off, assuming the gauge is accurate, 2 bar is fine for warm idle. Viscosity will affect pressure, so if you have used 20/50 before, the pressures will be lower with 10/40, and that's not a bad thing in itself. Overfilling can blow out seals. You would see leaks. 1/2 liter overfill would not do it. The car takes between 8 and 9 qts depending on how it was drained.