[AdamIsAdam]

Originally Posted by Sirrotica

The reason for the dipstick rising up is usually due to excessive crankcase pressure and it pushes the stick up as the pressure rises internally in the engine. Ring seal when you run the RPMs up can cause this as well as a faulty PCV system not allowing enough pressure back to the intake manifold.

When you open the throttle all the way the manifold vacuum decreases, and there is very little draw on the PCV system until the throttle plates are partially closed again causing a restriction and restoring manifold vacuum. By this time the dipstick is unseated and the pressure has found the path of least resistance to equalize the crankcase pressure to atmospheric pressure.

I have had Pontiacs when using synthetic oil that sealed the rings better than regular oil that actually caused detonation in a marginal situation, and actually cracked the top ring, causing blow by and excessive crankcase pressure. Unless you have an engine that is really close to maximum compression and detonation prone this probably isn't your problem. It may just be the synthetic isn't allowing as good of a ring seal as your regular oil did,or the engine is becoming tired and in need of a refresh.

Synthetic oil in an engine that is fresh, will definitely slow the ring seating process compared to regular oils. I have no idea what state your engine is in as far as fresh rings and being overhauled recently, another variable.

A leakdown test would be a good indicator of the condition of the condition of the engine valves and ring seal. A less scientific test is to disconnect the PCV system and remove the oil fill cap and observe the amount of blowby gases coming from the oil fill opening as you rev the engine, not as accurate, but if the amount of blowby is excessive it is at least and indicator of ring seal failing.

The oil pressure may just be to thinner oil when hot causing lower pressure. You don't state how much lower the pressure is. As long as you have 10 lbs. for every 1000 RPM you should be sufficient, I.E. 30 lbs at 3000 RPMs. If your not meeting that criteria, it may be time to do some investigating. Or if you've had a large drop in oil pressure, say 20 lbs. I'd be running some tests, maybe pulling the engine to look for problems.

These are things I've run into before, I'm sure others will add more to this.

My engine was built about 3 years ago with modest seasonal use only. It's 10.4:1 Butler 469 stroker on a 400 block. I have no detonation at all, even on pump gas.

I changed the oil filter from STP to K&N with this oil change too. I may switch that back in the Spring just to remove that variable and see if the oil PSI changes.

PCV: I am running one PCV from the passenger side valve cover to the carb base, non-ported, and also a Mopar type Moroso PCV/separator from the driver's side to the base of my open element air cleaner with the idea of pulling pressure out of the engine during WOT. When I bought the car last Spring, it had a bad leak at the rear main seal that a new seal didn't cure. The engine was using two open element breathers in both valve covers; no PCV. Changing to this new PCV setup eliminated that leak by about 95% or more. (The rear main seal was replaced by a friend just before I took delivery of the car.) Now I get a few drips of oil on the floor whereas before it was a small puddle.