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I read somewhere that when the oil evaporates, the leftover oil is effectively thicker, e.g., to extrapolate, 5W40 may be closer to 5W50 after the evaporation takes place than before so.

I use Redline Oil 5W40 (fully-synthetic ester) in my 2008 Jetta SE 2.5L with 80k miles, which requires oil of type VW 502 00.

Should I still top it up with 5W40, or should I go with 5W30 for top-ups?

I mostly live in the south (Austin, TX), and top-ups are only required past 5k miles (I don't change oil too often, since I use fully-synthetic ester).

DucatiKiller
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cnst
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2 Answers2

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Suggest you ask the person who wrote the article. While oil is a liquid and all liquids have an evaporation point, engine oils are designed such that the evaporation point is higher than any temps your engine will ever see.

Bob Is the Oil Guy is a site that has been around forever, and no one knows more about engine oils than Bob: https://bobistheoilguy.com/#

If you use a good brand synthetic oil with a viscosity according to your engine's specs, and change it within the interval specified by the oil maker, you don't have to worry about oil properties beyond that.

Thomas Carlisle
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As multigrade oil ages, the polymeric additive package breaks down, reducing the oil's ability to lubricate across a wide variety of temperatures. A 10w30 oil will eventually revert to the original 10 weight base stock. Utterly useless in warm season operation. No matter what oil you use, it accumulates contaminants, its detergents degrade, and by the time the 3000 mile mark is reached, the engine is being bathed in dirty, compromised oil. Use synthetic oil if you wish, but given its cost, and the necessity of timely oil changes, the costs may outweigh the benefits. A top quality conventional motor oil, with a 3000 mile oil and filter change interval, is your most economical choice for long engine life.

Greybird6
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