Quote Originally Posted by nadcicle View Post
Here recently I can honestly say I haven't kept track of miles because I just changed my intake manifold and I didn't spare any expense with the oil changes. I have probably done 3 in about 600 miles as I have been experimenting after the first change. The first change was to get any residual out of the system from doing the intake manifold gasket swap. Immediately I just happened to notice that once I drove an estimated 20 minutes or so the gauge for the oil pressure slowly dropped to the point that at stop lights it was at 0 and the CEL was on.

At the point of CEL I thought maybe something might have gotten caught up in the screen or oil pump somewhere so I changed the oil again without putting 60 miles on it from the last change. I drove it around for maybe another 200 or so miles and noticed that there was no change in the behavior of the gauge so I thought ok it has a lot of miles (eg 229k) so maybe it just wants a thicker viscosity as others have said that older engines require it because of worn internals. Since changing to the 10-40 the pressure is higher at start, but over driving it for the 20 minutes or so the pressure still goes to 0 at stop lights. I have just sorta tossed my hands up right now and kept driving it to a minimum, but can honestly say it doesn't seem to be pressure as when it drops to 0 there is absolutely no engine noise or excess shudder. Oh, and I live in Tennessee.

I will say that I am about to do 1 last oil change back to syn from this cheapo castrol I have been using as I was just using it to "flush" everything else out from having done my manifold gasket swap. I just didn't want to have to change it again if it was my sending unit and I had to drop the pan to do so.
You might of knocked the sensor when you where doing the intake gasket, they are quite sensitive and break pretty easily, and they are right there at the back of the block, so it's not hard to accidentally hit it. Don't trust what your gauge says, do the test I said, T-tap inline with the oil pressure sending unit and check the pressure with a manual gauge to make sure it has oil pressure. It's a simple test, it just takes time to get back there and set it up.

If the oil pressure test shows you have around 20-40 psi at idle, and over 40 psi under load, then the sending unit is bad, and you should replace it. If it shows you have no oil pressure, I'd start with the oil pump, remove the oil pan and check for a clogged screen, and might as well replace the pump while you are at it.

I highly doubt it's the main bearings or crank bearings, at 229k miles that engine has plenty of life left in it.