roundman

Difficult to say because if the bearings are worn bad enough, the rings can't be far behind and that means you really should be looking at a complete rebuild of the engine. How many miles do you have on the engine?? How hard has it been driven over the years?? This will be some clue as to how close your are to a full rebuild of the lower end. I would not just replace the bearings however. Do a compression test to see how well the cylinders are sealing, as this will tell you something about the condition of the piston rings and valves. Probably best to start saving up for a rebuild or new short block depending on the test results.

88GT40

well the reason i originally thought it was the oil pump is because i used somesea foam in the crank case i i didn't drain the oil right away, i drove it for a couple days and suddenly when it idled the pressure went to zero, so i had the oil changed and the pressure checked, so now i reset the idle to 850-900 and it keeps the pressure in the normal zone so i figure i clogged the pick up or screwed up the oil pump, or maybe the oil pump drive shaft might be twisted up.
by the way i have 109k on the engine and i'm sure it has been driven pretty hard what stang hasn't, i know the top end was rebuilt shortly before i bought it, but I'm not sure about the bottom end. I will have the pump replaced and will have them check the bearings while their at it and keep my fingers crossed.

roundman

I'm not familar with seafoam but I've heard it refered to as a carb cleaner, which means it's some kind of solvent. If you added this to the oil in the crankcase, this may have thinned out the oil or filled it full of air bubbles, both of which could have caused the oil pressure to drop. Since the pressure returned to normal after you changed this contaminated oil, then I don't think the oil pump or drive shaft is a problem. I would install a good mechanical oil pressure gauge and check the oil pressure at idle and then watch it as you increase the engine rpms. One rule of thumb for oil pressure is you need at least 10 psi per 1,000 rpms, so if you can maintain this, then you might not have a problem as big as you let it sound. by the way, you can check the oil pump drive shaft by pulling the distributor out which gives you access to the oil pump drive shaft as it is driven by the distributor via the camshaft gear. the shaft normally will not get twisted unless the oil pump seizes up, and since you have normal pressure, your pump is not seized up either. you should be using a 10W-40 weight oil also as this will increase the viscosity of the oil and kick the pressure up a touch too. Don't replace the oil pump until you have tested the oil pressure with a good mechanical pressure gauge!!!

88GT40

well sea foam is 100 percent petroleum, it can be used in the crankcase poured into the pcv tube during idle or as fuel injector cleaner.
now if i'm getting this right you say at idle it would be alright at under 10 psi, since idle is under 1000, or is there a cut off from which there is a minimum at idle then 10psi above that minimum for every 1000?
and why exactly is it that if i lower the idle just a little bit there is such a drop off that it would go from normal to zero, i'm beginning to think that my guage is the culprate, like i said i had the dealership check it with a mechanical guage and it was at 45 psi engine cold and as it warmed up it lower to around 30psi, but they didn't allow it to get as warm as it does during driving i dont know how much more that could affect the pressure, but i will have to start useing the thicker oil, i usa\ually only use 5 or 10w30, i was told a while ago that thicker oil isn't better for engines that have smaller clearances within.

roundman

you really need to get a mechanical oil pressure gauge installed so you can see what the pressure is!
for what it's worth, on my '88 stock engine with over 108,000 miles on it using synthetic Royal Purple 5W-30 oil, my oil pressure is around 50 psi cold and 40 psi when fully warmed up at idle speeds.