Here's the deal, just recently installed an L98 shortblock with about 80,000 miles on it before install. I put synthetic 5w30 in it to see how it would like it (stupid) and then after driving for about a week it began to smoke constantly out of the tailpipes (blue). At this point I began to think the piston rings were bad. I was told to try conventional 10w40 to see if that was thick enough to stay in the motor, well it still smoked. Now I even tried 20w50 and it still smokes with the motor running.

My question is this, is the motor just too worn or did i screw everything up by putting synthetic in and then switching back to conventional?

Also, the car has a gutted cat..someone told me if I put a regular functioning cat back on it would eliminate some or all of the smoke. This true?

Thanks as always guys..

 

Switching back and forth between synthetic and conventional oil didn't hurt anything.

Putting a cat on it won't have any affect on smoke, you'd just soon have a ruined cat on the car.

 

I was thinking possibly the old conventional oil that had built up in the motor over the years could have built a gunk "seal" on the piston rings, and the synthetic oil I put in broke these seals..now that seal needs to build back up. I read that this could happen somewhere here on tgo, but I doubt this is the case..

 

Changing from conventional oil to syntheic oil wont make the car smoke. Syntheic oil will help seal your piston rings and engine seals better then conventional oil. You could run a high milage oil with a slick 50 additive to seals your rings better. Or you could add slick 50 or lucas oil stablizer to the syntheic oil you already have in the car. Just drain out one quart of oil before adding the lucas oil stablizer. Did the engine smoke before you installed the engine? Did you rev the car up upon start up after you changed the oil? Putting the cat back on wont stop the smoke.

 

I'm not sure if the motor smoked before install, i picked it up used locally from another car and put it into mine. I tried the lucas oil stabilizer when the synthetic 5w30 was still in it, and it didnt really help much, if at all. The car currently has 20w50 in it but still smokes, I'd say it's a bit less than before, but it's still there. ..and no I didn't do any revving of the motor after adding the oil..

 

Or you can run clean regular oil (synthetic or dinosaur) with no additives and get the same results, but spend less money.

Forget about using heavy-weight oils, that's not doing anything except costing power. Running a heavy oil doesn't improve ring sealing, it's a band-aid to raise the oil pressure on engines with too much bearing clearance.

Have you done a compression test yet to find out if your rings are actually bad? If they are, the only thing that will fix it is a rebuild. There's no mechanic in a bottle.