TB2-X Thermo-Bob Kit


This kit is for 2006 and newer Kawasaki KLX250 and KLX300.


Port for 1/8 BSPP Temp Gauge?: * 


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 add your own Trail Tech Temperature gauge, accept the $14 option to get the version with the temperature boss.  The hole will be ready for you to add your own temp sensor with a 1/8-28 BSPP thread.  If you want to install a temp gauge later and want to use the TB2 now, go for the $20 option where we will provide a removable BSPP plug in the hole.


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