Thermo-Bob Kit Information

Bill Watson's Thermo-Bob is a replacement thermostat in it’s own housing that has a built in bypass circuit. It cleverly solves both of the problems with the stock Kawasaki thermostat. It’s higher temp thermostat keeps the temperature at the proper and stable 195 degrees, while the recirculation bypass system allows for faster warm up to operating temperature, a much more even temperature within the cylinder and head, and prevents an inrush of cold water by constantly circulating warm water back into the engine’s water inlet.  Bill's done his homework on this venture and his website has a wealth of info about it.

The device comes in a kit with everything you need other than hand tools ( little more than a sharp knife, screwdriver and a basic socket set ) and fresh coolant.

All the parts you’ll need come in a neatly boxed kit. 

The kit includes-

  • The Thermo-Bob
  • Tee fitting with hose barb
  • 2 small hose clamps
  • Piece of bypass hose
  • 4 large hose clamps
  • a small, fat O-ring
  • 1 tie wrap

KLR650 Themo-Bob Kit Contents

From the beautifully machined device itself, to a single zip-tie to secure it, all is included in the box. The instructions that are e-mailed when you order the kit are among the best I’ve ever seen. There are several pages, with color photographs (in fact, the photos in the instructions are so good that I’ve decided to use many of them here) Where necessary, the separate components in the photographs are color coded, and the parts breakdown and any possible future maintenance is all covered therein. The supplied hardware is of outstanding quality ( though I would've preferred phillips to slotted fastener heads on the hose clamps ) and the machining of the main thermostat housing is outstanding. By the way, you'll recognize Bill's machinist for this device as none other than Eagle Mike of Eagle Manufacturing.


In it’s most basic form, the install goes like this. Pull the tank and shrouds. Drain your coolant (when cold of course). Ya pull your old low temp thermostat, and put the cover back on with the new o-ring. Then cut the hose that connects the old thermostat housing to the radiator right where it crosses the valve cover to head junction. Insert the Thermo-Bob device there using the supplied clamps. Measure and cut the return line from the radiator to the pump. Install the recirculation “Tee” fitting there (again with supplied clamps), and connect the “tee” fitting to the bottom of the Thermo-Bob device with the supplied bypass hose and clamps. Use the supplied Zip-Tie to hold it in place. Replenish your coolant. Reinstall the tank and shrouds. Enjoy the peace of mind that you’ve added years to the life of your engine. It took me 45 minutes with notes and picture taking and the installation of a digital temp probe.

During the install, I saw little need for departure from the well written instructions. One thing I did do however was  ( instead of removing it ) to simply hang the coolant tank from my turn signal stalk with safety wire, just to save a minute or two.


You'll notice in the picture above that I've got an extra electrical panel that rests behind the coolant tank. Even with all these extra "space sinks", the Thermo-Bob installation was well thought out and there still remains plenty of room.

As I said, there is little I can add to the excellent instructions, but I'll throw in a picture or two to give ya an idea of what it looks like in the real world.

Below is the ( in my case ) installation of the temperature probe for the Vapor Digital instrument panel. This was a great aid in testing, since the manufacturer claims a 195 degree thermostat opening ( that is by the way, EXACTLY what I saw ).

Thermo-Bob Installation

You'll also see in the above picture the location of the first hose cut, where the new thermostat will be located in the Thermo-Bob housing.  Below is another view.  I used a razor knife to make the cuts, and cut out an extra 1/4" ( though it looks like more in this photo ) for the device to sit.

Thermo-Bob Installation

The device is actually a little wider than the 1/4" inch I left for it, but the extra hose helps to hold it away from the cylinder head. You can alter yours as needed, but start small, you can't add hose once you've cut it.

Below is a shot of the thermostat housing installed. Notice the hose clamps aren't tight yet. This is to allow you to "aim" the bypass fitting on the thermostat housing at the bypass "t" fitting later in the install.

Thermo-Bob Installation

Now, specific measurements are given in the instructions as to where to cut the radiator return hose for the bypass "t" fitting. Simply measure and cut, install the bypass "T" and the clamps, and before tightening the clamps, you'll want to "aim" the thermostat housing bypass fitting and the bypass "t" fitting at each other. It makes for a cleaner install. Then you can tighten the clamps.

There is a supplied bypass hose and clamps of course. I installed mine to the Thermo-Bob thermostat housing first with it's clamp, and then routed it down to the bypass "T" fitting. You'll see in the picture below that the supplied hose is a bit too long. The reason for this is so you can add some upward support to the thermostat housing by cutting the hose a bit long so that the Thermo-Bob will "rest" on the bypass hose.  I cut off about half of the extra ( shown in the picture ) hose leaving it about 1/4" longer than the bottom of the barbed fitting on the bypass "T".

Thermo-Bob Installation

Not much to it after that. Check all the hose clamps, use the supplied Zip-tie to adjust the position of the thermostat housing as needed ( I didn't need it ), fill with coolant per the instructions, reassemble, and ride.

Here's how it fits in after final install. ( remember, the wire to the inline temp probe for the Vapor, is not part of this kit )

Thermo-Bob Installed

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