TB2-R Thermo-Bob Kit

Kawasaki cut corners in the KLR cooling system, and the Thermo-Bob 2 modifies your cooling system to operate like automotive systems have for decades.  Thanks to the dual radiators, a stock KLR250 runs 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.  The data plots are attached on the right from a KLX250, which is also a dual-radiator bike.

The Thermo-Bob 2 is a machined, hard-anodized aluminum housing that bolts directly to your cylinder head. 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 as the 250 plots above show.