Question 1: My dealer says I have to use the OEM lubricant in my motorcycle or my warranty is void.
Answer: This is not true and may, in fact, be illegal. Have the dealer put this in writing on his letterhead. We doubt he will. All you need to do to fulfill your warranty requirements is to use a lubricant that meets or exceeds the OEM specifications. Spectro products meet or exceed all manufacturers performance requirements.
Question 2: Can I mix viscosity grades?
Answer: Yes, you can and no harm will be done. Topping up with 10w40, if its all you have available, will not injure the 20w50 in your crankcase. It will, however, lower the overall viscosity of your crankcase oil to a certain extent. This will cause no harm to your motorcycle. Likewise, adding a 20w50 product to 10w40 will slightly increase the overall viscosity in your crankcase. Again, no harm will occur.
Question 3: What is a multi-weight lubricant?
Answer: A multi-weight oil is an oil formulation that acts as if it has two different viscosities, depending on the temperature. At the lower test temperature (40C), it flows as the first number would indicate, and at the higher test temperature (100C), it flows as the second number would indicate. This multi-weight nature is made possible by the addition of long-chain polymers to the oil, which are coiled up when cold, but straighten out when hot, and thus change the flow characteristics of the oil. Thus a 10w40 oil will flow like a 10 weight oil when at 40C (fairly thin), but will not thin out more than a 40 weight oil would when hot (100C).