Hi All,  My 73 has abnormal oil pressure and I really don't know what to make of it.  It runs a steady 70psi once warmed up (pegged when cold), and at highway speeds, once the rpm reaches 3000 (about 75mph) the oil pressure slowly decreases and starts to fluctuate as the rpm is increased.  At about 3200 rpm (about 80mph) the oil pressure reads around 60 and fluctuates about 5 psi, at 3400 rpm (somewhere between 85 and 90) the pressure is about 55psi fluctuating 5.  I just drove it 2,400 miles from Calif to Texas like this.  I kept the oil topped up, but not over filled.  It used a quart about every 400-500 miles.  Ran fine otherwise. I am thinking several things:

1) bad guage (Possibly, but not likely)

2) Wrong oil pump (hi perf oil pump)

3) stuck oil pressure relief valve? Is this integral to the pump, I can't find it in my shop manual?

Any ideas?? Has anyone seen this problem before?

Thanks, John

Well, I downloaded the parts manual (6 pdf documents), and the oil pressure relief valve is built into the oil pump.  When I have the pan off to replace the connecting rod bearings, I will pull the pump and see if I can determine if it is original.  When I sold the car in 82 with 86k miles on it, it was original.  The car now has 152k miles and ? number of owners since, so who knows.

John

High oil press. can damage some parts of the engine, like bearings, and cam/distributor gears. If you are gonna pull the pan to do bearings, it would be plumb silly to not replace the pump.
I would check the pressure with a mechanical gauge, just to see what it really is, just out of curiosity. Alot of people think a high pressure oil pump is cool, but in reality, it is not. High volume is the way to go. Maybe someone put a high press. pump in to mask the bearing noise, and perhaps prolong the inevitable.
Loose/worn brngs. can cause the fluctuation in pressure at speed.

Thanks Joel,  That is what I was thinking.  Someone who owned this car was clueless mechanically.  I suspect a hi press oil pump was put in, and I agree when I drop the pan the oil pump will be replaced regardless.  Is there an aftermarket Hi volume oil pump which would be good for the L48 350, or should I just go stock?  I assume the Oil Pressure guage in the 73 is mechanical, so there is no electrical sender, just small tubing going to the guage.  Where is the oil pressure tap on the block?

John

Melling makes a good pump.  And you can get it at Autozone for less cash then many other places for the same pump, including NAPA.  The oil line will either connect near the oil filter, or up near the base of the distributor.

John, you are correct about the pressure gauge being mechanical. That don't mean its correct, tho!
The pressure tap for the gauge is on the driver's side of the engine, down by the clutch linkage, above the oil filter. There should be a small, 1/8th" black plastic line(unless its been replaced) going to the gauge. There is also a tap in the top of the block at the rear, next to the distributor.
You can get a Mellings high volume pump at just about any decent parts house, around $20-$30 or less.

!! Ken beat me!!! Adams' Apple38819.8281365741