TB3-N Thermo-Bob Kit
This kit fits all Ninja 250s: From 1988 to 2012.
Kawasaki cut corners in the inexpensive bikes, and the Thermo-Bob modifies your cooling system to operate like automotive systems have for decades. In stock form, the Ninja 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. The plots on the right show measured data from the KLR650, also a single-radiator bike.
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’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 of a Thermo-Bob on a KLR650 can be found here.