Originally Posted by 63mako

So your saying it runs at #25 at cruise but if you let off the throttle the pressure climbs to #45. I see no way this could even happen. That said both of the other posts are just plain wrong. A SBC needs #10 of oil pressure per 1000 RPM. If you get that running 10W-30 it is fine. If your idle pressure jumps to 35 or 40 at idle with 20W-50 is it better? No. That said Mobil 1 10W-30 does not have adequate ZDDP for flat tappet cam protection and additives are not the way to go.
Synthetic has a lot of benefits over conventional oil too numerous to even go into here but a major one is drastically improved cold start protection where 90% of engine wear occurs.
A thinner oil has many benefits over a thicker oil also too numerous to even go into here but a major one is that oil is not only a lubricant but a coolant for internal engine parts. Lower viscocity oil has more flow volume even though pressure is less cooling the internals better than thicker viscocity.
True synthetic oil is not a problem in any Chevy V8 in good condition with good gaskets and likely the main reason your car engines are running 300,000 trouble free miles and your diesel has 450,000 without a rebuild.
There are so many myths and misconceptions out there on this subject and they just keep getting spread by being repeated over and over. Read deep into the oil sticky and do some in depth research on this to clear up the myths.

Originally Posted by 63mako

First point, If Mike Ward has information that would contribute to the thread post it. If not why post? I see no sense in playing trivia games in a thread. Or you can sit their until someone comes up with a logical cause then post "Yes! That is exactly what I was thinking". Either way it just seems like ego stroking.

I have been thinking about this and might have a couple possible causes of why the OP is seeing this strange oil pressure issue. The smaller molecule synthetic will drop oil pressure some accross the board running the same viscocity as conventional due to its ability to flow through smaller gaps than conventional.
1. Worn main bearings or thrust surfaces could be the problem. When the engine is under load the crank is pushed down into the bearing cap. Oil feed holes are at the top so this opens clearance up where the oil is under pressure resulting in pressure drop due to the small molecules being able to escape the gap faster than they can be fed in. When you let off the crank is freewheeling with less downforce and more uniform clearance at all points on the circumference of the main bearing journals with less oil (pressure)escaping.
2. Worn oil pump. Similar situation. Gears are loaded different under load than when engine freewheels. Gears or case could be worn more where they mesh under load and less where they mesh when freewheeling.
The smaller molecules could be why these symptoms show up with synthetic and not conventional if one of the above problems exists in the engine.
I don't know for sure if either of the above scenerios would cause the issue but it has been provoking some thought on the subject.
that a heavier weight synthetic may clear the oil pressure drop under load issue up. I would try and figure out the underlying cause though.

Originally Posted by billla

Mike, if you've got the solution or a perspective - just share it.

The intent of the forum is to help fellow Corvette owners, right?

Originally Posted by Mike Ward

...My best guess...

Originally Posted by Mike Ward

My best guess is that the engine was not actually filled with sufficient oil.

Originally Posted by billla

Um. Certainly a possibility; I considered this but on a fresh fill it seemed unlikely.

Originally Posted by Mike Ward

No, just thought that anybody and everybody had done it at one time or another.

Originally Posted by billla

I have definitely been broke...but I can't say I've ever intentionally under-filled a crankcase.

I did have a car where I bought oil in the 5-qt jugs every time I bought gas

Originally Posted by byocum

Changed oil at Mechanic Shop. Watched them pour oil from quart containers. Then checked it myself after they pulled it out of shop. As i don't trust anyone with my new toy. A little over full if anything. So it could have been foaming up & pump cavitating at higher RPMS. I have been around engines most of my life. Just thought it was a weird experience. Thanks everyone.

Originally Posted by Mike Ward

Well OK, but I'm surprised with the combined experience here that only one other guy hinted at it.

My best guess is that the engine was not actually filled with sufficient oil. I've seen it a hundred times- low oil level causes a pressure drop at higher RPM which quickly recovers at lower speed. Nobody else used to have to choose between spending their last dollar on gas and beer instead of a quart of oil?

Originally Posted by scottyp99

Mike, post #31 mentions low oil level as a possible cause, shame on you for continuing to tease after the answer was given.

And, what is up with all of this arguing about oil, when the important question is: what kind of spark plugs should I run?


Keep the shiny side up!
Scott