TB2-X Thermo-Bob Kit

Kawasaki cut corners in the KLX cooling system, and the Thermo-Bob 2 modifies your cooling system to operate like automotive systems have for decades.  In stock form, the KLX250 and KLX300 run too cool when ridden in temps below about 100F. The cooler outside it is, the worse a stock bike is. Plus, the factory cooling system relies on surges of cold coolant every 30 seconds at the bottom of the cylinder to control engine temperature… check out the plots of actual measurements!

The Thermo-Bob 2 is a machined, hard-anodized aluminum external thermostat with a coolant bypass. It allows coolant to bypass the radiators during warm-up, speeding warm-up and eliminating the surges of cold coolant year-round. It also raises the operating temperature at the top of the cylinder to 195°F from 158°F… more importantly, it raises the operating temperature at the bottom of the cylinder to 185°F from downright cold, (I’ve measured temps below 30°F). The warmer temps should extend engine life as well as increase oil change intervals, and improve economy by a few MPG. It was the first product to ever receive a 10-out-of-10 rating at Patman Racing, and was strongly recommended by the late Cary Aspy, who was the original developer of the 685 and 705 KLR big-bore kits. Cary also liked how this gave more consistent carburetor jetting.

A full technical write-up on a 650 can be found here.  The 250’s dual radiators make a stock bike’s temp swings even more erratic than a 650 – see the before and after plots above – they are all over the place when stock, and super-stable when the Thermo-Bob is installed.

If you’d like to know what your coolant temperatures are, you have options while completing your order. You could upgrade to our Thermo-Bob “2A” that has a machined boss in the side for a temperature sending unit.  You will choose one of the following four options:

Option 1) No temp gauge at all, the Thermo-Bob 2 is fine as-is.  (No additional charge).

Option 2) You could upgrade to our Thermo-Bob 2A with an included Trail Tech digital Temperature gauge ($80 upgrade).

Option 3) You could upgrade to our Thermo-Bob 2A  without a digital temp gauge.  We would place a removable 1/8-28 BSPP plug in the 2A so you can add your own aftermarket gauge at a later date ($30 upgrade).

Option 4) You could upgrade to our Thermo-Bob 2A without a digital temp gauge and without removable 1/8-28 BSPP plug so you can add your own aftermarket gauge as soon as the Thermo-Bob arrives at your house ($25 upgrade).