TB3-KA Thermo-Bob Kit

This kit is for 1987 to 2007 KLR650s that use the aftermarket 10 gallon fuel tank. If you have a stock steel fuel tank or aftermarket 6.6 gallon tank, you can use the Thermo-Bob 2 kit.

Kawasaki cut corners in the KLR cooling system, and the Thermo-Bob modifies your cooling system to operate like automotive systems have for decades.  In stock form, the A-model KLR runs too cool when ridden in temps below about 80 – 85F. 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 – just look at the plots of measured temperatures.

The Thermo-Bob is a machined, hard-anodized aluminum external thermostat with a coolant bypass. It allows coolant to bypass the radiator 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’m measured temps below 30°F). It should eliminate the out-of-round cylinders that are common to the KLR as it ages which usually results in increased oil consumption. 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 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 can be found here.