Switching to synthetic oil

[dsldude]

A warning about switching to synthetic in an older engine: oil seepage! I bought some name brand oil that was on clearance for our gasoline cars and both were seeping oil much worse than before. Turns out the clearance oil was full synthetic. Both cars have high mileage (120K+ and 200K+) which probably plays a factor.

I agree with this statement. Leaks can happen when switching. Actually on that note, I have found that when you have a lot of seepage, you can do some extreme low mile oil changes and actually slow or stop the leaks. My theory is that if clean oil is constantly passing through the seals and helping to reseal and condition them. This proves very true on MTB and dirt bike suspension which I work on frequently so I believe it to really help on cars too. I think I have now slowed or stopped my t case leak this way this month. Whatever you do just stay away from additives in the oil.

I think you should just stick to conventional if you are pulling and making long trips. It's interesting science behind the heat characteristics of synthetic vs conventional as well. Conventional will pull the heat from the motor and retain it and hopefully cool it as it passes through the oil cooler. Synthetic traps it in the parts, and the oil runs cooler while the parts run hotter. It's really hard to say what option is better. I'm old school and run conventional in everything. I would change it once a year if you are only between 5 to 10K per year and not stop and go. If you live in super dusty conditions maybe a bit more often. I would be more concerned with keeping fresh diesel and clean fuel filters in it.