Oil Pump Replacement?

94 gmc safari panel van 170000 miles
oil pressure is low at idle after warm-up. at cold start it seems fine but when it warms up its low and motor knocks (Dont laugh yet) this knocking is only at full temp at idle this has been doing this for 40000 miles it has not goten worse nor better I let a 16 year old kid borrow it and it kame back that way I keep racing oil in there and have pulled boat 150 miles to the lake 4 times last year in 100 degrees any how I wander if I pop in a new oil punp what do I have to loose thought someone would like the story about this old work horse

I think I would try a heavier oil and see if it goes away.
If it's been doing it for 40,000 miles, I don't think it can be too serious.

My guess is front main is bad but not too bad. I keep 60w racing oil in it now I think I should add a oil cooler and see if that helps first.

Check 1st, but I thought it already has a cooler - I know my '97, and several of my friends' came with them from the factory.
I was thinking of an oil like 20w-50. If 60 won't keep the pressure, maybe the engine just has too miles on it.
If it's fine at speed, and only a problem at idle / no load, I think I'll suggest driving it until it quits. If the bearings are loose, at least they're washed well.

Has it been checked with a manual oil pressure test gauge to be sure it is low?
MT