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I ride a 2015 Yamaha FZ-07 (around San Francisco / Bay Area), which is water-cooled and supports 10w30, 10w40, 10w50, and 20w50 motorcycle oils.

However, the manual says not use 10w30 oil when the ambient temperature exceeds 70F/21C (and recommends 10w40 or heavier instead).

Why are lighter oils contraindicated for hotter ambient temperatures?

If I use a full synthetic oil (which is probably going to be hardier), is it still bad to run a lighter oil when it's hotter outside?

The engine temperature itself is much hotter anyway, and stays pretty much the same (180F/82C) no matter what the ambient temperature is.

DucatiKiller
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ManRow
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1 Answers1

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If the oil is too 'light', then it will be too thin when hot. Ambient temperature absolutely affects engine temperature, or at least it can. That is counteracted to a large degree in a modern, water-cooled engine, but it's probably there out of caution, standards from an earlier time, and general best-practice.

If it says above 70F don't use the light oils, that means that that oil won't be suitable in non-cold temperatures--if you're almost always in the highest range of heat your engine is rated for, that's too thin to be ideal, and you'll see faster wear on the engine.

A 'full synthetic' oil will just have fewer impurities, by the way, but that doesn't affect how you should interpret its rating. Viscosity and temperature is consistent with rating, fully synth or otherwise.

tl;dr: follow Yamaha's instructions to get best life of engine. You'll probably sell it before you ever see the effects of whatever oil choice you make, of course... But it's good karma to take care of an engine that new. ;)

Kyle Baker
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