To replace or not to replace (oil pump)
 

Patient - '95 Z28 120k miles. Engine internals are stock except for a new cam

My oil pressure is normal for our cars as I understand. It is about 20psi at idle and approaches 40psi on the highway on 5w-30 conventional oil.

However, I have the engine out of the car doing some other repairs. Should I go ahead and replace the oil pump even though I have no indication of a problem?

Cost is not the factor it's the "if it ain't broke don't fix it" adage that's on my mind. But I do have the engine out of the car which makes the job much easier. But I don't want to introduce a problem. Also it seems that somewhere I've read that pressure is really dependent upon the condition of the bearings, etc. that the oil is pumped through and that an oil pump primarily provides volume not pressure. Pressure is caused by volume forcing its way through passageways.

So looking for sound reasoned advice here.

Re: To replace or not to replace (oil pump)
 

I would at least change out the drive shaft with one with metal coupler. You'll get differing opinions on whether to change the pump. A new pump should not introduce any problems. Just use a good casting like the Melling 10554, use a stock pickup and make sure you check the drive gear for any issues. MHO is, if you are going to keep the car for a while, change the pump while it is easy to do and you don't have to think about it for a long time.

Parts list:

Melling Select 10554 pump (std vol, 3/4" inlet. Should come with Melling IS-55E shaft with metal coupler and 70# pink spring).
GM pickup tube, 12550042 (3/4").
GM oil pump drive gear 1103868 (if needed).

Re: To replace or not to replace (oil pump)
 

Thanks Rob, got the parts on the way.

Re: To replace or not to replace (oil pump)
 

For anyone interested in the hows and whys of oil pressure I found this informative video.

Re: To replace or not to replace (oil pump)
 

And a good article on oil pressure if you prefer to read over watching a video. Also explains the roll of the spring in some oil pumps.

Classic Inlines Performance Parts - Understanding Oil Pressure