I know what the oil pressure is supposed to be: between 1 and 2 bars at idle, and immediately pegged at 3 at any engine speed over idle. Most of the time, my oil pressure is fine.

However, immediately after an extended high-speed drive (e.g. anything more than 30 minutes on the interstate), my oil pressure is lower than it should be by about half a bar. At idle, the needle is just barely over
the 1 mark, and it doesn't peg at 3 until higher RPMs are reached (I don't have a tach, so can't give exact RPMs). After a hard highway drive, in 4th gear (manual trans) it won't peg until about 50 mph. If I'm just driving around town, never getting on the interstate, the oil pressure is fine; after short trips on the interstate (my daily commute is about 10 minutes of interstate each way) it's also fine. However, the low pressure after a hard drive concerns me.

I'm using Castrol 20W50, which I've always used. It doesn't burn much oil, if any - I have to add about half a quart every 1000-1500 miles, but some of that is leakage from around the valve cover gasket, oil filler cap, and crankcase ventilation tube.

I'm guessing the oil pump has an impeller of some sort - is this prone to wear? For that matter, should I even worry about this issue since my oil pressure is fine *most* of the time? I hope to keep this car for another 250k miles as my daily driver, so I want the engine to last.

Thanks.
- Nathan
'83 240D, 250k miles