I know enough about cars that I think I know the answer but thought I'd post anyway. I've got a 90 that I recently bought and it is going thru oil pretty bad. Good thing I checked it because it was down 2 quarts. That kind of set off the alarm bells. It smokes on start up and will smoke lightly if you are sitting at a light idling for a while. Both of those things are typical of bad valve seals but I feel it is using to much oil to just be seals. It does not smoke under hard acceleration or when downshifting and letting the tranny slow it down. There is a trace of blow by out the vent hole in the valve cover but very minimal. I'm kind of thinking rings but if that's the case I don't really think it's worth putting a motor in it. I've got too damn much invested in it already and I'm afraid if I did the motor then it could be the rack or pump that goes next or any number of things. It only has about 70K on it so I don't know why rings would be shot already. Bummer!

 

I'd do a compression test, then add some oil to the cylinders and see if it goes up by a considerable amount. A leak down test would also help you figure out what's going on as well.

 

Intake could be sucking oil in from the valley.

 

Did you use a new gasket on the oil pan bolt?

 

Sorry you lost me on that one?

 

A properly done Leak Down Test would tell you the health of the piston rings. It is a test that will help you identify where the oil consumption is coming from. It won't help with with bad valve seals but it is a very useful test. The compression test is useful but in your case I would prefer to do a Leak Down to have a better idea "what" is causing the oil to burn. Wet/Dry compression tests are useful to identify the particular cylinder that might be making trouble.
Leak Down Tests are used on piston powered aircraft and are done annually to monitor the health of the engine. Eastwood sells the tool and you will need a fairly powerful air compressor to do the test.

A 31 year old Corvette with 70 k miles means it probably sat at some point. Things get stuck and seals harden when left for a long period of time. How long have you had the Corvette? Have you changed the oil yet? Is the engine noisy at all? Is there any oil on the oil filter area that could be coming from the rear Intake gasket (China Wall)? The oil pressure switches are known for leaks as well, clean it up and make sure that no oil is leaking out anywhere. What is the vacuum reading when your engine is running at idle?

I helped start a Corvette that had sat for 2 years. We filled the engine with Kerosene instead of engine oil and started the engine. We let the engine warm up and shut it off and then drained out the kerosene right away and then filled it with fresh oil and filter. Do Not put the engine under a Load (like driving) with kerosene. It is simply there to clean out the insides of the engine and loosen up the parts like Lifters and such. You could substitute Marvel Mystery oil for the kerosene if it makes you feel safer. After doing this the lifters were nice and quiet like they were and the motor once again purred. The thin oil like kerosene will get into all the nooks and crannies and suspend the junk until you drain it out.

 

The garage floor under the car has about 3 oil marks less than an inch in diameter so leaks can't be the issue. I just did a round trip of roughly 120 miles and went thru 1/2 a quart of oil. At that rate I'll be using a quart per tank of gas. I will go ahead with a compression test and possibly a leak down test but at this point I think I know what we will find.
The weird thing is there is no engine noise, and no smoke coming out of the exhaust under hard acceleration. It pulls hard and runs well. There is very little blow by coming out of any of the valve cover openings. I'm stumped because it is definitely not showing any visual signs of that rate of consumption.
I bought the car last fall and put it into storage right away. I'm sure the past owner laughed all the way to the bank.

 

Check the area around your #7 and #8 spark plugs - see if you have oil seepage that comes from underneath the plug body onto the head....

 

A few posts back I said that it wasn't leaking but thanks for your response.

 

It's possible that there won't be much smoke out the exhaust even if the engine is burning oil. I have seen this before. I know it sounds strange especially going through 1/2 quart in 120 miles... most engines burning oil will smoke at some point (accel, decel, puff after idling, etc). Does your car have catalytic converters?
You mentioned a little blow by from the valve cover openings. I'm not very familiar with the L98 PCV system, but my LT1 has two crankcase vent pipes: one for venting during intake vacuum conditions (between the crankcase and the intake manifold) and another for venting under acceleration (between a valve cover and the air filter side of the throttle body). I mention this because I doubt if you should be seeing any blow by at all from either of the valve covers. This just doesn't sound right.
Also, you insist the engine is not leaking yet there are 3 oil spots on the garage floor. This is a bit confusing. However small the oil spots are, they clearly indicate a leak.

 

It does puff out a puff of smoke on start up, usually in the morning after it has sat for the night. It will also put out some smoke if you let it idle for a lengthy period of time but nothing on accel or decel, even when I get on it pretty hard.
Yes the car has a catalytic converter.
Yes it is leaking a bit but my point was that for the loss I'm experiencing there would have to be a puddle and as said there are only a couple small drops. I can't even for sure attribute them to the Vette as there is pretty big dried up oil circle from past cars.
I am still trying to arrange an appointment for a compression check/leak down test.

 

Are you looking in the mirror to check for smoke when driving? Best to get someone to follow you and tell you what they see, there can be quite a lot of smoke that you only notice when following rather than relying on looking in the mirror.

 

Ya I hear you. Can really see it in the dark in the headlights of the following car. Certainly nothing conclusive but Ill give it a try. Bottom line is the oil is disappearing and I don't know of any magical way for that to happen. Too much oil for valve seals so that likely leaves just the rings. Damn.

 

Have you pulled the plugs? A fouled plug may point to a problem I just got rid of.

https://www.corvetteforum.com/forums...rning-oil.html

 

I had the plugs changed about a month ago and not many miles. I have a call in to the mechanic and he's supposed to call me back. Hoping he remembers their condition. He didn't mention anything at the time which I hope he would if there were issues.

 

Just run a compression test. If you can do plugs, you can do a compression test. Do it dry and then wet and see what results you get.