.15Pro or 2.5 Nitro Rustler? Anything over 270* for the 2.5 is considered overheating. In 15* weather, even the factory "rich" break-in setting of 4 turns out on the HSN is way too lean. I am nearly 5 turns out on the HSN this time of year and it was "warm" today at 45*. Engine temps were in the 240-250* range.

You may want to cut some holes to direct air over your engine if you have not already.