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I just wanted to run this theory past you guys to see if you agree or have a different theory.

- 10-30 in engine from the beginning of the car's life with no smoke at start up

- Added STP Oil Treatment to crankcase and smokes at start up(less than 30 seconds)

- Change oil(removing the STP Oil Treatment) using 10-30 and no smoke at start up

- Next oil change decide to try 10-30 high-mileage oil and smokes like crazy at start up

- Quickly drain high-mileage oil (about 50 miles) and go back to 10-30 and no more smoke at start up.

My theory: The higher viscosity oils are having trouble making it through a drain hole that was designed for thinner oil and therefore staying on top long enough to find their way past worn valve seals.

What do you think?

1998 Mazda Protege, 169,000 miles  

the thicker oils have problems getting wiped off the cylinder walls cold by the low tension oil control rings that most newer engines run...

there is a compression ring.. usually with a straight face against the cylinder wall.. ]

a second ring with a sometimes a  tapered face to scrape oil down... \

and then the oil control rings... =    behind the oil control rings is an expander to try its best to keep them against the cylinder wall.    scraping most of the oil that gets splashed up off the cylinder wall and through the holes or slots in the piston..

when engines get over heated  the rings can get trapped by carbon  and not expand and contract as the piston goes up and down the slightly tapered cylinder bore..

when oil fails to get changed often enough this can also happen..

running the same weight oil as you always have is usually best..  10 30 is to thick for a lot of newer cars..  many use a 5/20 or 5/30..

most japanese designed motors can run 220,000 miles..  some a lot more..  

Yes, but if it's smoking because of the reason you mentioned, wouldn't it be doing it all the time and not just at start up? This is why I suspect leaky valve seals but I'm not a mechanic.

So you think the rings are coked and maybe I should try pouring some kerosene into the spark plug holes?  

i don't think i would try to UNCOKE the rings.. with kerosene... it might work... but i think just running conventional weight of oil without the sticky gluey stuff...

if it does not smoke with conventional oil... GO with that..

you could have valve seals starting to go...  but as i recall.. you have 180K miles on it.. time to start putting a few bucks a week away for a new /er car or a new motor...  

Appreciate it wayne.