CR4A Thermo-Bob Kit


This kit is for 2002-2008 CRF450Rs and the 2005-2018 CRF450X.  If you have a 2017 or newer “RX”, you need the CR4C or CR4D kit.

Add Spare Thermostat * 

The Thermostat is the only consumable in the system, some people get one now for the future.


We’ve seen our share of CRF450s used as a snow bike, and in those applications, the lack of factory cooling system control leads to cold coolant temps.  There is no factory thermostatic control, so coolant temps can vary widely, then these carbureted bikes have inconsistent jetting.  The Thermo-Bob 3 is a machined aluminum housing with a 180°F (82°C) thermostat inside, and modifies your cooling system to operate like automotive systems have for decades… keeping coolant flowing all the time through the engine, but not through the radiators until it is up to a selected temperature.

There is also a threaded port in the Thermo-Bob 3 that will accept aftermarket temperature gauges such as the KOSO or TRAIL TECH 1/8-28 BSPP temperature sending units.

A full technical write-up when used on a Kawasaki KLR650 can be found here.