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Replace Synthetic oil in the car with Conventional: Good or Bad Idea?

I just bought a car that has had Synthetic Oil run it for a long time. Would it hurt for me to switch back to conventional oil. I have heard that it can ruin the oil gaskets and seals. Is this true or car folklore?

You can switch back and forth all you want between regular or synthetic oil. They mix so well, they sell oils that are a blend of regular and synthetic oils.


No problem switching, but why would you want to? The synthetic is a very good oil, better in every way I know other than a little more expensive, which you likely will get back with a little better mileage.

The old story about not mixing goes back not quite as long as I do. The oils and materials used then are not the same as todays. There is no mixing problems.

Why not keep giving it the ‘good stuff’? It’s only a little more expensive–probably an extra $30-40/year for most people, and you can run it a little longer than dino oil if you want, offsetting some of the cost. Plus it will give you a little better mileage and (subjective opinion) your car will be smoother and quieter.

Dino oil and synthetic oil are exactly the same chemically, except that synthetic allegedly has more consistant size molecules and has fewer impurities. They can be switched back and forth and even be blended…you can even buy them already blended.

There is, however, one caveat: always check your owners’ manual to be sure it does not specify synthetic. Some do, especially on engines with turbochargers. Turnbos run at extremely high speeds and are heated by the hot exhaust, so the oil used to keep them lubed and to take some of the heat away is subjected to higher heat stresses than in normally aspirated engines. Synthetic seems to hold up better to heat stresses, so some manufacturers spec it for their engines.

While the Prelude may not require synthetic, I felt it was important to mention the above because a wide range of folks read, and hopefully take some information from, these threads.

You will be fine as long as Honda doesn’t recommend synthetic oil in the owner’s manual.