I got my 425 in september of 03. When I first got it the fan worked but after using the machine for a while it seemed to get hot found the fuse where the wires comes through the hood and it was blown replaced it with a larger fuse and it ran but only intermittenly, got to checking out and it had a loose wire at the fuse fixed that and all was well.
power trac 422, and agco-allis 5660, ,1845 power trac Greenworks CRT 426
My 422 which I have had for four and one half years will run a good while before the fan kicks on in cooler weather if I am not using the mower or roto tiller. In this weather I can run it at half throddle or les for probably 30 minutes or more before the fan kicks on. Just put your hand on the oil tank and you can pretty much tell if the fan should be running or not.