I noticed there is not much mention of the Thermo-Bob on the KLX forum. It's a really well-made thermostat system that corrects an inherent design limitation of the KLR 650, as well as the KLX 250.

The stock coolant setup continually dumps cold coolant into the the cylinder, and doesn't let the engine warm up very quickly. In cold weather, this is severely magnified. Since the 250 bikes don't have a temp guage, I guess it's a matter of "out of sight, out of mind".

I've run a Thermo-Bob on my KLR for a couple of years. It makes a BIG difference. I just installed one on my KLX today. These things theoretically should increase your engine life by getting the temp up quicker, and keeping the cold-dumping process from occuring.

Watt-man makes them...out of Arizona. Check it out if you are interested in the engine being as efficient as possible, and lasting as long as possible.

 

Blackheart, being the consumate expert that I am on all things Thermobob...cough...cough...I will say this. Having had some KLR600/650's, IMO the 650's were wildly varying in their coolant temps. I often wondered if the twin rads on the 600 were better in somehow having superior flow, more capacity, or whatever, because I never saw the sometimes wide and quick temp swings to the degree I did on the 650's. You'd slow down and pick your way through technical stuff at low speed, and temp guage would shoot up and the fan would kick in. Then you'd break out on pavement, and especially if it was downhill, the needle would plummet to cool. Now, that was a needle guage, but after 2 KLR600's and 2 KLR650's, both 650's were identical in this respect.

My KLX250/300 has a Vapor inline pickup in a rad hose and a digital guage. You can see every move in coolant temp quickly. I am quite impressed with how stable the temp range is on the KLX. There's a reason you hear so many say how infrequently the fan comes on for this bike. Something seems to be well designed in the cooling system...and of course, it's not a 650cc single...which helps. The KLX doesn't seem as much of a candidate for the Bob perhaps? And so ends my WAG on this issue.

 

Amazing how the klr survives with just 1 radiator and a fan, gets hot on the gauge and will run the fan non stop but never had one boil over.

Ran a klr one summer with a gutted stat and the the temps were more consistent on the gauge, actually think it was better. But then winter came and it never seemed to get warm on my morning commute, so put a stat back in.

If your into having a bypass for the stat KTM uses one on the 300 (other models too) that is simply installed in the hoses. A KTM BOB if you will.

 

Rim...you never had the rear end pee syndrome on your KLR? You know how people gather around some of the parking/stopping areas on the high off road passess in CO and other places? You've just climbed and climbed on a sketchy jeep trail and pull in beside some other people gawking at the scenery. One time as soon as I had stepped off and was taking my helmet off to do my turn at gawking, another gawker kind of yelled out. I turned to see a stream of coolant shoot out at least 6 feet on to the shoes of the gawker. Needless to say I redirected the fire hose to a safer angle at camp that evening. They direct that hose out the back to keep a boilover from hosing down your rear tire, but apparently parallel to the ground isn't ideal.

 

Never seen that one, but sounds like lots of fun! here's a pic of my latest overheat story happened just last week to a buds Husqvarna TE310, after a long grind up a steep mountain trail he stopped. A couple seconds later 2 hoses exploded spraying a ball of mist like a bomb went off. Seems husky uses a higher pressure cap than there cheap hoses, LOL. We fixed it up with pre bent heater hoses from the auto store and stole a cap off another bike just in case that was defective.

 

Wow!...impressive. Yeah, that was a heck of rad cap...or cheap hose...or both. You know...I've only seen a rad hose bust on a car where the hose was pretty old. I've seen 'em pop off a clamped end with a newer hose. Those hoses couldn't be very old on that Husky though.

 

The problem with the KLR, and in many ways, the KLX, is that they do not run HOT ENOUGH much of the time. The Thermo-Bob addresses that issue by allowing them to heat up much quicker...then, stay at a decent temp, even when it is cool out. The gulps of cold water directed at the cylinder can't be good for wear ratings...the Thermo-Bob addresses those cold gulps of coolant.

When it's hot, the Thermo-Bob simply works like it should, without getting "in the way". I run single-track and hillclimbs on my KLR 650 in these 110 + degree temps in the desert, and have never overheated...except the time my fan fuse blew...and I saw that on the temp guage and allowed it to cool off.

So, I'm using this on the KLX to make sure the coolant gets up to good operating temp (190+) quickly, and stays there. If I'm not wrong, I think the stock thermostat is only a 160....plus, the way the cooling system is designed, it can't help but allow gulps of cold coolant into the cylinder.

I hope he makes one for the Honda CB919 I have...that bike runs way too cold, too.

 

There was a thread about the thermo-bob on here, and I recall people thinking it was less necessary on the KLX, but I dont recall the specific why. now I gotta go reread it! However, it seems like premature cylinder wear is not a big issue on these bikes?

 

It depends upon your definition of premature. If you could significantly increase the amount of miles before having to sweep the jug and go up one size on the piston, that would be the goal.

 

Some KTMs have something similar - an X configuration as the coolant leaves the engine it goes to a temperature controlled switch at the center of the "X" where it either gets routed into the radiators then eventually out the bottom of the right radiator and back into the engine.

Or, if the temperature has not risen sufficiently, the coolant leaves the engine, hits the "X" switch, bypasses the radiator circuit, and gets directly into the bottom of the right radiator where it immediately enters the engine again.

The idea is to keep the oil hot enough for good flow and of the right viscocity to spray nicely out all the little nozzles inside the engine directing the oil to all the important bearings, crank, cams, etc.

Some KTM's use a Y configuration that does not have the temp switch and doesn't try to do any of that. In looking at my new Husaberg, it has the switch.

I can see two benefits:

1) Brings the oil up to temperature more quickly. Most engine wear happens when you first start it until the oil warms up enough to flow well. That's why you should never just hop on a cold bike, fire it up, and start riding hard without letting it warm up first. Lots of parts are not getting good oil coverage and the oil is cold and thick.

2) In very cold weather, it keeps the oil from cooling off too much and becoming too viscous to flow well. See #1.

I was curious about claims of better cooling if you eliminated the "X" and replaced with the "Y" for higher flow, so I set up a whole experiment with sensors on the cylinder, left and right radiators, and recorded the temperatures under very controlled conditions. It was very clear that the "X" definitely allows the coolant and engine operating temperature to come up to temperature more quickly than the "Y" - by a couple minutes.

And then over a long duration where the temperature reached steady state, the "X" cooled every bit as good as the higher flowing "Y" config. So there really didn't seem to be any benefit to going with the "Y" instead, and the "X" setup did have some benefits.

Anyway ... it's late, and I'm rambling. Long story short, the thermobob looks to be the same thing as the KTM's "X" coolant flow setup as well as on the new Husaberg's. Not sure of other bikes that use it, but I'd say it's probably pretty common. The idea seems to work as advertised, anyway.