Oil Change Question

If I recall, the manual for my 2004 wr450 says 20w 40, but I went to the shop and they didn't have any in stock. The guy told me 10w 50 would work and probably would be better for the hot weather. He said:

The 10W means it is not as thick during starting and will actually make it easier to start than using 20w

While the 40 is not as thick when warmed up as 50, so the 50 means it will give me better protection in the hot weather.

Can someone please confirm?

I'm going to do a bit of research and will report back my findings, but I'd like to know what you guys are running and if my understanding is correct.


I should just try searching before typing...

Though I still would like to know what other wr450 riders run for oil?


The way that oil viscosity is measured is by its weight. In this case, "weight"

refers to the thickness of the oil. Any liquid has some viscosity and that

viscosity changes depending on its temperature. Usually, viscosity (thickness)

decreases as temperature increases. This also is true of engine oil. Engines

need a thin oil at startup, so that it can get to the engine components

quickly, but it needs a thicker oil when the engine is hot because a thin oil

becomes too thin. This is why engine oils are supplied as dual-grade weights.

When you see 10W-30 on a quart of oil, it means that it acts like 10 weight

oil when it is cold (the "W" means winter, say -10^C), but acts like 30 weight

oil when hot (100^C). This is not to say that it is actually thicker when it is

hot. Hot 30 weight oil is thinner than cold 10 weight oil. Even so, it still helps

provide the benefits of both types of oil depending on its temperature. So

0W-30 oil acts like 0 weight oil when cold, but maintains a 30 weight viscosity

when hot. Think of it this way: when your engine is hot, there is basically no

difference between 0W-30, 5W-30, and 10W-30 oil. They are all acting like 30

weight oil at this point. It's at cold startup, when almost all engine wear

occurs, that the viscosity is different. The 0 weight oil will get to the engine

components quicker than the 10 weight oil, but in reality cold 0 weight oil is

still thicker than hot 30 weight oil. On the other hand when the engine is

cold, there is no difference between 10W-30 and 10W-40 oil. However when

the engine is hot, the 10W-40 oil is thicker than the 10W-30. This is why

single-grade oils are very bad. Straight 30 weight oil is way too thick when

cold to properly lubricate the engine. The only way to use single weight oil is

to have an oil pan heater to bring the oil up to operating temperature (about

140^F or 60^C) before the engine is ever started. If you simply must use it,

this type of oil should only be used in race engines with pan heaters.

As far as what oil viscosity is best, it depends who you ask. The fact is that

engine oil maintains its viscosity better than ever and synthetics maintain it

the best. In my opinion, the best viscosity for all weather is 5W-30. The

reason is that both 5W-30 and 10W-30 breakdown at about the same point.

Lighter oil can get into places that the heavier oil cannot and will get there

more quickly, even when cold, so why go heavier? The only reason would be

leaks. If you have oil leaks, a heavy oil will go through them more slowly. That

is why you can buy "No-Smoke", which is basically sludge to thicken your oil.

If your engine is sealed well, feel free to try Mobil 1's 0W-30 oil. If that "0"

really makes you nervous, stick with 5W-30. 10W-30 is uneccessarily thick

when cold

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