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This question already has an answer here:

I've heard in the past that when you have one of the two types of oil (Synthetic or natural) you shouldn't change between them when you do an oil change.

But I just called to change my oil and got told that, well, you can switch between the types, just don't mix them in the same oil mixture.

So what is right? Can you change oil type while doing an oil change?

marked as duplicate by Solar Mike, Community Jan 16 '18 at 17:24

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  • Have you searched for this question on here - it would be worth it.... – Solar Mike Jan 15 '18 at 21:11
  • One possible problem may arise when changing to synthetic in an older car. The excellent deterging capabilities of synthetic oil may actually introduce an oil leak in older cars, where gunk from the oil mineral oil held the leak just shut. This isn't mentioned in the question which is referred to, so i though i'd add that here. I don't know of any other reasons why it'd be bad to mix 'em. – Bart Jan 15 '18 at 21:39
  • Bart, good point. The synthetic may also loosen and circulate the gunk. – TomO Jan 15 '18 at 22:00
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I do not think that there is any issue in switching between oil types only thing you need to be sure is that you use the correct oil viscosity as recommended by your manufacturer.

Also there is a belief that synthetic oil would deteriorate the seals and gaskets and leak into engine. Synthetic oil has not been shown to deteriorate engine seals or gaskets. But it might find an existing leak. The smaller molecules of synthetic oil are able to pass through very small cracks and crevices that the larger molecules of petroleum-based oil cannot. Eventually, those small cracks and crevices can lead to bigger problems — with or without synthetic oil.

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Switching from conventional oil to synthetic oil at the time of an oil change shouldn't be a problem, provided that both the old oil and the new oil are both advertised as being compatible with all modern conventional or synthetic oils.

There are some engines, however, that have specific oil requirements. Or, more specifically, they have certain additive requirements. If the manufacturer recommends a specific, specialized oil type, it's probably best to stick with that type of oil, especially if you want to follow the manufacturer's oil change schedule.

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