I have 20-40 in the bike now.. will it hurt if i go to 10-30 because im about to change it and im just wondering if it would potentially create problems. and what si the difference between the 2. Thanks.

Mike

 

The lower number is the rating at which the oil flows at a cold temperature, and the second number is what it flows at a high temp. Basically, the higher the number, the slower the oil flowed. So, if you have a 20 as a 1st number, it means the oil is flowing slower (thicker) at cold temps than a 10 would at the same cold temperatures. On the second number, if you have a 30, it means that it flows faster than if it were a 40. So basically, you would be switching to an oil that is better suited for colder temps on both the low temp and high temp conditions. Keep in mind though, the numbers ratings are not related to each other, such as the oil does not get thicker as it gets warm. there are two seperate number scales for cold and hot conditions.

This is done so the engine gets the oil as quickly as possilbe upon start up, but the oil is not so thin it can't protect once the engine is warm. Its known as multi-viscosity oils.

You really should try to run the correct viscosity for the bike. Chances are pretty good its suppose to be 10-40. I think most bikes run hot enough to warrant the 40 designation in the second number. I wouldn't run a 20-40 or 20-50 unless you live in a relatively hot area. Some manufacturers will recomend different oils for different areas, but 10-40 is probably the best all around oil that will protect in most environments.


The thing to remember is oil has a film thickness. You should try to run the oil your bike was designed to run since all engine components are designed around that oil's film thickness at operating temps. If you go too thin, you have less film thickness and less support with bearings and other clearance parts. You have to remember, your bearings and the mating surfaces aren't actually touching. There is a small clearance, and the oil fills that gap so you don't have metal on metal contact. to thin of an oil, and there won't be enough protection and the bearings can actually float back and forth a little.. to thick of an oil, and not enough new oil gets between the bearings. The oil acts as a support.

of course, this is all on a scale of ten thousands of an inch difference. But after a long time, it can make a difference.

as for hurting the bike from changing viscosity oils. No, it will be fine. You can change to what ever oil you want and not have any issues from that itself.