I just changed the oil out in my 1966 Toronado to synthetic. Coincidently I am getting a little smoke in my exhaust. At the same time as the oil change was a carb rebuild and new water pump.

Is it possible that the synthetic oil is bypassing the rings and getting into the combustion chamber when the regular oil didn't? I did notice after the carb rebuild that on startup the engine is kind of lumpy but ultimately smoothes out when warm. Could this be oil fouling a plug until the engine warms up?

I am no mechanic (wish I were) but seems to me that after a carb rebuild and new oil the 425 should run like a top. Prior to the rebuild (first one for the Qjet) I had some serious hesitation at tip in but no lumpiness.

Kind of confused... what do you think?

 

I'd guess lumpiness due to choke/choke pulloff/idle mixture adjustment. No opinion on oil smoke, but check your PCV.

 

jmo, but it sounds like your motor is not a fan of synthetic oil if there was no smoke when using conventional oil. your valves seals/guides may be a little worn, or your rings may be letting more oil by due to wear. you also may experience oil leak issues with synthetic. i'd switch back to conventional oil, myself.


bill

 

Since you just had the carb rebuilt I would go back over the choke and Air/fuel settings as mentioned above.

I agree with Bill on synthetic oils.

 

There are about as many opinions on using synthetic oil in older or high-mileage cars as there are people offering them.

Remember that your car was built decades before synthetic oils began to become commonplace, and running something like synthetic oil in it was never contemplated or accounted for by the engine's designers.

Here's what I think is an interesting take on the topic.

http://autos.aol.com/article/synthetic-motor-oil/

His suggestion is that, no, running synthetic in a higher-mileage engine is not a good idea, and the problem you're experiencing seems to be very similar to the problem he describes with his Neon.

I agree with those who say you should put conventional oil back in. The old maxim always applies: if it ain't broke, don't fix it.

 

Thank you all for your thoughts. Sounds like I'm going to drain the synthetic and put back in some of what Mother Nature put here for my 425! I really hate paying for something just to undo it but in this case it sounds like conventional oil is better than synthetic.

When I replace the oil I'll check on the carb settings.

Thanks again for your opinions,

Jeff

 

I agree 100% with your words. The new synthetics slide right on through every spot it will find. The newer cars have tighter tolerances & synthetic works fine, nevermind if u have some higher miles that just makes matters worse. Go back to some good ole 10-30 & u will probably see the smoke go away.. I know guys who never had any leaks in their engines & then decided to go synthetic & within a week or 2 the drops of oil are in the driveway...Just my opinion from some of hwat i have seen...Best of luck with it..

 

Yes, you never use synthetic in a high mileage engine unless it was used from the get-go. You can break an newly rebuilt engine in on fossil oil and then switch to synthetic at the first change, but even then it's no guarantee that these old engines will make the best use of it.

Synthetic doesn't allow the rings to seat as well as conventional so on a street motor you could get some blow-by when using synthetic even if the engine is new.

 

It was a tough pill to swallow... draining 6 quarts of brandnew synthetic out of the car only to fill it with good 'ol 10w40.

Guess what... no more smoking and after I ran it out and got the engine nice and hot the startup is now normal.

I really appreciate the knowledge everyone shares on this forum... who knows what I would've run into had I not simply changed the oil.

Now if I could only find the short in the steering column that is draining my battery.........

Jeff

 

Glad to hear that your problem has disappeared.

Perhaps you could put the drained-out synthetic back in the bottles and take them back to the store for a refund. After all, the oil is only a little dirty.

 

Glad it all worked out, we know how it feels....

 

If it makes you feel any better I thought my motor needed a rebuild as after I changed the oil and filter to 10w30 it started smoking badly after leaving from a intersection.So I drained all the oil out to go to a 20W50 and it still was smoking so I was sweating thinking that the motor had to come out ! BUT as it turned out the transmission modulator was bad and was sucking trannie fluid into the manifold at idle ,so I installed a new modulator and voila ! no more smoking !!Ya gotta think like a 1970's mechanic to care of these cars.