[QUOTE] [QUOTE] So... I'm taking the XT660 to the frozen north. There's a chance that temperatures may go down to -25 or less... I am worried about starting the bike. If it's very cold surely the oil thickness may make it sluggish to start. [/QUOTE] (snip) Very true. Virtually all cars in use in northern Norway have engine heaters fitted, there is a reason for that. I would have tried out different alternatives for gently heating the lower engine[1] from anything from below -20°C to closer to 0°C before trying to start it in the morning. Primus (or whatever you have) at various settings& distances from the engine, not to burn the engine paint. [1] if the XT uses the frame as oil "tank" (as some other offroaders do) this obviously doesn't work 100%[/QUOTE] Being a lifelong Swede and inhabitant of the frozen north myself, I concur with the herring-scoffer. Stay away from slippery oils which _will_ ruin the clutch, use an oil recommended by Yamaha and on cold mornings, preheat the engine with whatever is to hand before running it to help it to start and reduce the chance of lubrication failure. Another possibility, if it's a dry sump engine, is to siphon/drain out as much oil as you can and heat it up in a tin over the stove, which might seem too fiddly but beats hell out of having your bike catch fire from overenthusiastic application of the Primus.