The manual recommends using 10w40 down to 14F (-10C) or 20w40 for down to +32F (0C). Online I see that 15w40 is rated for 14F as well.

What would you guys suggest to be the lowest safe operating temperature for a klx250 with a 351 big bore kit running rotella 15w40?

Thanks

 

When you say "operating" do you mean running it or starting it? Bob is the oil guy states all oil listed at 40 will have the same characteristics when at 212 dF. So all would perform the same at operating temperature. Now the cold start is a different animal...

The initial weight or flow of the oil when cold is clear, the lower the weight the thinner it is at start up. The problem here is the fact that Kawasaki lists 10w at 14 dF when it seems it should go lower based on the oil company recommendations having 15w go that low.

From this I would think that Kawasaki is saying something different than what a safe cold oil flow would be. It appears they think their bike will still start reasonably well down to 14 dF with 10w, so I would think they would feel 15w might cause some starting issues with the drag on the starter, not really anything to do with the lowest recommended temperature for oil use. If you use their logic the 15w would be good around 23 dF

Now if you want good starting below 14 dF it seems it would make sense to go to a 5w or 0w to get the lowest safe operating temperature and best starting temperature.

Short and sweet, the oil company is saying where they think their oil will lubricate adequately, Kawsaki is saying where they think their bike will start best. Make sense?

I use 10w40 motorcycle oil most of the time, but now I am using the 15w40 Rotella because of the price and rating - it is JASO-MA rated, meets motorcycle specs. I don't ride much below 30 dF and if I did I'd either be starting a bike that sat in a heated garage or focus a spot light on the clutch cover, it's amazing how warm a light can be in that kind of use.


In a side note, I used to block off one side radiator on the KLX when running in the below 40 dF range, the left side (non-fan). I would stick a piece of a soda twelve pack I cut to slide behind the louvers. I never did have the fan start, so I have to think it would most likely keep decent engine operating temperature. You might consider that for the cold weather with your 250. You would know quickly if it was too much, the fan would start and run when the engine got to that range temp.

 

I have been running at -20C (-4F) for 4 years now, no problem with 5w30.
Nothing to block the radiator either.

 

Wow thanks klx678. Lots of good info in there. I may try that spotlight method.

And thanks for the input duom. Ill keep that in mind for next winter.

The reason Im inquiring on the 15w40 is because I know 5w40s have a tendency to shear. Even though it is 25F today, I was hill climbing in +70F the other day with my fan constantly running, so I need an oil that will retain its viscosity.

According to Kawasaki standards a 15w40 is actually recommended down to 26F. Would you guys personally feel comfortable starting your engine outdoors in 26F with a 15w40?

If not Ill hold off until warmer weather, but run rotella t6 5w40 next winter.

Thanks!