I have a 1992 RS that I just had the original 305 swapped out with a 350 L98 from a 1989 firebird(rebuilt). Now for some reason, im going through ALOT of oil. Like 2-3 qts after only driving 70-80 miles. Yet, no leaks where I park it. Not a single oil spot. And it doesn't seem to be burning oil, because it doesn't smoke at all. I even went and got UV dye to add to the oil because I couldn't figure out where it was going. So I added 1oz. of AutoPro UV dye to my oil after filling it to the appropriate level, drove through town and down the highway for about 20-30 mins. Then I got out the blacklight and checked for leaks. But I could not find ANY sign of oil. Nothing lit up at all. Other than that, the car seems to run great. Im stumped..... The only other thing I can think of is I know it still has the original ecm from the 305, and the esc module is from the 305. I don't know if either of those could have anything to do with the massive oil consumption though..... Any thoughts or help would be much appreciated. Thanks

 

Rings installed incorrectly, bad valve seals or 2 much vacuum on the crankcase from pcv.
Or a combo of any of these things

 

What oil are you using? Synthetics when they burn out the tail pipe dont smoke.

 

If the engine us using 2-3 quarts in 70-80 miles, I think you'd see it. Either out the tail pipe or on the ground, no matter what kind of oil you're using. That is way crazy oil consumption.

Who did the rebuild on the 350? Did you do it or did the person you got the engine from just say it was rebuilt?

I ask this because I'm wondering if the oil returns in the cylinder head are plugged up and all the oil is up on top. I've seen this happen....to me.

 

Castrol gtx high mileage 20w50 synthetic

 

considering not even 2 stroke engines burn that sort of oil volumes something is seriously f'd

and if its not visibly leaking then its burning. it cant really go anywhere else

 

If the motor was rebuilt, why use the (gimmick) high mileage oil??
Also, use regular oil for a fresh motor.

 

Have you tried pulling your spark plugs and looking at them to see if they are oil fouled? also are you checking the oil with the engine cold? Try to look behind you when the engine is under a high load, if you see blue smoke, its burning oil.

 

Its synthetic oil. You wont see any blue smoke with synthetic

 

Try switching to a conventional motor oil at 10w 40. I have read others had a simular issue with excessive oil loss into an unknown abyss while using Synthetics and made a switch to conventional oil and cured the issue