5-10 lbs after warm up @ idle is not good.
it could be that the oil is to "Light", ie: 20wt, or that its diluted with gas, but I doubt it.
More likely the mains and rod bearings and cam bearings are worn, and/or the oil
pump needs to be rebuilt.
In either case, first try to change the oil to SAE 30wt, or use 20-50 multi grade (yea, I know its not "recommended", but you're not going to hurt anything) and see if it helps.
If it does, run with it.
If it doesn't, you're looking at a rebuild.