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Q: Does synthetic oil cause leaks in older vehicles?

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Hi,

Following link describes that synthetic oil may cause leaks in older model vehicles.

https://www.yourmechanic.com/article/can-you-switch-between-regular-and-synthetic-motor-oil

However, myth vs fact link below addresses exactly the same question and contradicts with what YourMechanic.com explains.

http://www.pennzoil.com/en_us/education/know-your-oil/why-synthetic-oil.html

Which one is true?

Thanks for your help and time.

A: Opinions vary pretty widely with this topic...

Opinions vary pretty widely with this topic. For the most part, if a vehicle's engine has spent most of its life using conventional oil, it should stick with conventional oil. The full synthetic blend has more defined and uniform molecules. So where an older vehicle using conventional oil may have never had an oil leak, you may start to see oil leaks with the more defined, uniform, and "more slippery" full synthetic oil. Conventional oil may leave deposits that can, for lack of a better term, "plug" a small leak where the full synthetic oil with the better detergents will wash away these deposits and the leak becomes more prominent. An older vehicle with newly installed seals may have a good experience with full synthetic oils. If you have a newer vehicle which was engineered to use full synthetic oil, use full synthetic oils.

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