yellow warning light - temp/gearing nytro

The snow is probably tight at that temperature and your not getting enough cooling. Try running some ice scratchers .

running 18/40 on my 09 mtx 162

Some people have had issues while others don't The Nytro cooling system has always been inadequate even in cold temps. there is no real air flow threw the radiator and or engine compartment to begin with. I also never realized until this year when i actually installed a tunnel cooler and removed the OEM radiator that the inlet and outlet of the OEM radiator are actually in the middle of it. So actually you only get benefit of half the radiator to begin with. Its just a poor design. You take that and the lack of air flow threw it and you can have problems regardless.

First thing i would check to see if the the fan is operational. if it doesn't come on that would block the majority of what little air goes through it. I would also check coolant level to make sure there is no air in the system. Run it with the cap off to see when the thermostat opens if the fluid level drops. Also some well placed vents in the cowling can help get the hot air out from under the cowling
as far as gearing the MTX's were geared 21-20 top and 40 bottom and there has been a long debate on gearing them down verses not. Quite a few people have said that 19/40 is great. Some people have gone down to 18/40 and said the same thing. I believe the 2011 and newer sleds came with 18/40 to help with bottom end with the factory boost option to help with turbo lag down low. I have a 163 with stock gearing and never had any issues.

Good sleds but they have a few flaws that you just have to deal with. you either like the nytro or you don't it takes time to figure out which camp you fall into. good luck and enjoy the snow you have we don't have any in the Reno/Tahoe area at all its scary because Reno gets its water from the snow pack

I have never had any issues with cooling even with the turbo installed. I have a temp gauge and I have never seen it higher than 170, usually would run in the 120 range in powder. I would look for air in the system also.

I have 19 40 gearing and I have ridden another almost identical sled with 18 40. The lower gearing is better from a stop but not much difference after that. If you change I would go to an 18 40. I think you would like the difference.

If you are going to go with lower gearing I would go to the 18 top gear. you might lose a few mph on the trail (if you are one of those people who like to go 80) but it is otherwise better.