I have a 1991 f150 5.0. When it is wormed up the oil pressure drops to 2 -3 LB on both the after market mechanical gauge and the stock dash gauge (both new). The pressure stays at 50-60 above 2000 RPM. I have changed oil with 10-40. I can see a oil leak (mist)at the fount of the intake by the distributor. Could this create the drop in oil pressure at idle? Thanks for any help.

 

Nope. There is enough wear somewhere to cause the low pressure maybe or the pump is worn out. At idle, the relief spring in the pump keeps the relief closed or it's supposed to. A new oil pump might help. i don't know if they are available but the hot rodders of old put high volume oil pumps in their modified engines which would increase pressure at idle and would maintain pressure better at high rpm.

 

I would agree with a worn oil pump.
If your seeing 50 psi hot at 2000, that's still very good.
If the main and rod bearing clearances are getting wide from wear, I don't think your 2000 pressure would be that good.
The pump is right up front and driven by the distributor tip through an extension rod.
The drive for both is taken off the camshaft integrated gear.
If you can get the oil pan down far enough, the pump can be changed.
For the cost of a pump and pan gaskets, it may be worth the effort otherwise use some STP oil additive in the oil to help out a bit longer.
Good luck.

 

How many miles on this pup?

 

Thanks

 

110k