After my issue with bad ethanol, I filled up with E0, and thought my issues were solved. I drove it 70+ miles and all was good, no oil usage. Next trip of about 90 miles, I got home and it was 1 qt low on oil. This seemed to happen suddenly. Normally used 1 qt. in 700 miles =/-. No high RPM driving >3500.

PS - Not the Corvette, but another Chevy.

Checked the PCV valve and it rattles, no excessive oil noted.
Did a cold compression check and have #1 - 175, #3 - 170, #5 - 187, #7 - 170, #2 - 180, #4 - 180, #6 - 180, & #8 - 175. I double checked the compression thinking I might have a broken compression ring from the lean burn of the ethanol, but these numbers don't show anything. Have not done a leak down test yet. No noticeable smoke at hot idle in the garage or on restart.
I pulled a couple of plugs when checking for damage after the ethanol and they were 'white' and very clean, but no noticeable electrode damage. I pulled all eight for the compression check today and now have a bit of black carbon on the plug and some with a bit of oil on the threads, but none oily on the electrodes. The plugs are Bosch Platinum WR9FP R6 671.
The engine is a 350 +.030 with L79 cam and 10.5 / 1.0 forged pistons but ~9.5 to 1.0 with composite head gaskets under 462 camel hump heads . About 100K+ miles on the engine.
Any thoughts on where it is going? I do have some minor leaks at the front crank seal and rear main seal.
Thanks in advance.
Ron

 

Ron, how many miles on the engine? Sudden oil usage on a sbc is usually valve seals.

 

Thought of valve seals, but never thought of immediate beginning. No noticeable smoke on startup. It does have ~100K on the engine. I raced it for a few years in a Vega before swapping it to the 68RS. It is due to be freshened up, or build another one. The only way to check the seals is to pull the springs, right?
I think I'll hang a couple of white towels over the tail pipes and see what I get.

 

You mentioned PCV but how does air get in? It could be stopped up there. Any chance of a partially restricted exhaust or the choke partially on? I would think that if it was burning 1 qt. in 90 miles there should be noticeable smoke and a very sooty exhaust. This sound more like a leak that only occurs at high speed so back to increased crankcase pressure and note that a rattling PCV is not a sure test nor does it indicate that the breather or the baffle is clear.

 

The PCV is in the valve cover and air in from the fill tube at the front of the intake. I do have a lot of chassis oiling under the car, but can't find the drips at idle in the garage. Could be blowing out the front or rear seals at speed, I hope. Might try that "BLUE ????" rear main sealer.
R66 327 had stuck oil rings but it was smoking even at idle.
I'll check the vented cap and also the PCV vacuum tomorrow.