we know the temp by a temp monitor like the one that duratrax sells or by a probe like the venom smart temp has, the temp outside doesnt matter, as long as your engine maintains about 220 you are good, if tis really cold outside you might want to put liek a paper towel around the head, when it is tuned correctly during break in, it should be about 220 or so, read this http://www.rcuniverse.com/forum/m_55...tm.htm#5522803