66 mustang oil pressure problem

I have a 1966 mustang coupe with a 289 2bbl. Several months ago, there
was a terrible clicking comming from the valve train. To my great
disgust, my oil pump had died. I replaced it with a high volume pump
(cheaper than the regular ones...go figure). I also replaced the
lifters and push rods. The heads were rebuild about 2 years ago, so
theyre still good. Now when i start the car, the engine sounds really
good and i have good oil pressure until it reaches operating
temperatures. The pressure drops until it reaches 25psi (20W50 oil to
compensate for failing rings) then it holds for about a couple of
minutes, then the pressure drops slowly down to 0 and smoke starts
spitting out the tail pipe at idle. There's no knocking and no ticking
so i assume the valve train and bearings are decent. Could it be the
high volume oil pump?

Ive had the car garaged for several months in hopes of saving up for a
rebuild. I start it up about once a month so it doesnt seize up on me
and every time it sounds beautiful and every time once it reaches
operating temps it does this. Any ideas that would hold off a rebuild?
Or anything i should look for when i do rebuild? Thanks!

sirerrol wrote:
> I have a 1966 mustang coupe with a 289 2bbl. Several months ago, there
> was a terrible clicking comming from the valve train. To my great
> disgust, my oil pump had died. I replaced it with a high volume pump
> (cheaper than the regular ones...go figure). I also replaced the
> lifters and push rods. The heads were rebuild about 2 years ago, so
> theyre still good. Now when i start the car, the engine sounds really
> good and i have good oil pressure until it reaches operating
> temperatures. The pressure drops until it reaches 25psi (20W50 oil to
> compensate for failing rings) then it holds for about a couple of
> minutes, then the pressure drops slowly down to 0 and smoke starts
> spitting out the tail pipe at idle. There's no knocking and no ticking
> so i assume the valve train and bearings are decent. Could it be the
> high volume oil pump?
>
> Ive had the car garaged for several months in hopes of saving up for a
> rebuild. I start it up about once a month so it doesnt seize up on me
> and every time it sounds beautiful and every time once it reaches
> operating temps it does this. Any ideas that would hold off a rebuild?
> Or anything i should look for when i do rebuild? Thanks!

You mentioned that the heads are good, but it almost sounds like the
oil return path in a head or both heads are plugged, not allowing oil
to drain back to the pan. The smoke would be from the valve seals being
flooded with all the oil stuck up in the heads. If the engine is in
good shape, there is no reason to have a high volume oil pump or to use
20W-50 oil.
If the drain holes in the heads are open, you have a bearing problem,
probably camshaft bearings for starters. You mentioned that the rings
are bad and I bet there are more problems to this engine than rings.
I would pull a valve cover to make sure that the return path is open
(if the heads are less than 2 years old, the valve cover gasket might
still be good) and if the heads are clean switch to a 5W30 or a 10w30
as a last attempt before rebuild. My $.02 worth.