quote:
Originally posted by Malibu:
Rick, Toyota emphatically advises owners who switch to synthetic to stay with synthetic and not ever go back to dino. There are seal shinkage and expansion issues involved with switching back and forth that can lead of oil leaks. Example: if a rear main seal leaks 5-10 years from now it might cost you over $1000 to get it fixed.
That is not correct. It might be from the dealer you use, but it surely isn't toyota's stance themselves. Fact is, there isn't anything to the effect of what type of oil except by api certification which both mineral and synth can meet.
I don't think I've seen anywhere a study that establishes seal leaks from switching back and forth. I can also assure you from personally being involved with toyota corporate and local dealerships that there is anything to state such by them. If it is, I'd like to see this.
The only way oil MAY cause seal leaks is if you're running a sub-grade dino oil past its intended usefulness, and it allows crud to accumulate on the seals, then lubrication cannot get to the seals, thus they dry out and the only thing keeping the seal from leaking is the coat of crud, then changing to a good synth where they oil has a better cleaning ability, and it cleans off this crud around the seal thereby cleaning off the existing seal that the crud has maintained, then it would begin to leak.
IMO, and not fact, I'd say this issue would not occur provided you don't over extend your oil beyond its limits this will keep the engine clean eliminating this condition.
Personally, I'd also consider just staying with one brand/type of oil just to keep everything simpler for convenience sake more than anything as either way, synth or dino, will give you more than adequate protection.