Price of the Thermo-Bob kit is $115 including S&H as of July 21, 2008

Introduction & Cooling System Background

Engine temperature is more important than most of us understand. And consistently keeping your engine in a certain temperature range is even more important still.

There are a couple of reasons for this, so let me take a second and tell ya about it.

Modern performance engines are to a large degree reliant upon clearances. Clearance between the cams and the valve stems, clearances between the crank and its bearings, and of course clearances between the piston and the cylinder walls.  Too much clearance and the parts rattle and beat themselves to death quickly.  Too little clearance and an engine seizure is the result. Certainly we’ve all heard our engines make a little more noise and rattle when cold, and we’ve seen the result of high temperatures causing a crank or piston to “lock up” or "seize". Both cases are bad, very bad. This is why we always let the engine warm up to temperature before we ride, and try to control the high temperature as we ride.

Now we all know that metal expands with heat and contracts with cold. Knowing all about this, the design engineers that built your engine allowed for the engine to operate at an optimum temperature where the metal parts have expanded to a specific size, resulting in the perfect clearances for best power, and longest life. Anything to either side of this optimum temperature and obviously the opposite is true… diminished power and shortened engine life.

Surely I don’t need to tell you about the importance of engine oil in the longevity of an internal combustion engine. But what you may not know is that the oil also has an optimum temperature at which it works best. And once again, allowing the temperature to move outside of this optimum range even for a short period of time is detrimental to the life of the oil…and thus the engine itself. The oil needs to be hot enough to freely flow into all the tiny spaces that require it, and also hot enough to boil off the water and combustion contaminates that naturally accumulates in the oil as a byproduct of engine operation. Yet if the oil gets too hot, it quickly ( almost instantly ) breaks down, looses it’s lubricity, and is ruined.

So hopefully now you can understand that temperature control in your KLR650 engine is not just about controlling the upper end, and the boil over point, but also controlling the lower end as well, to keep the internal components and the oil hot enough to work best and last the longest.  Hot enough to work properly, not so hot as to ruin the engine or oil.

KLR650 Cooling System

The engine temperature control system in the KLR650 is fairly simple. The engine generates heat. The liquid coolant is there to take that heat to the radiator via a pump. Air takes the heat from the coolant in the radiator and the process starts over. The upper end of the temperature range is controlled by airflow through the radiator. This is accomplished either by forward speed through the air (and maybe airflow enhancements like the Patman Radiator Mod), or by way of an electrically controlled fan to assist with airflow if the engine temps get too high.

The lower end of the temperature range is controlled by the thermostat in the cylinder head. This device blocks the flow of coolant to the radiator when the engine isn’t hot enough to operate properly, and allows coolant to flow to the radiator when the engine starts to get too hot, thereby stabilizing the engine temperature at that optimum range we spoke of a minute ago.
 
Liquid cooling in internal combustion engines has almost become perfected. Take a look at the temperature indicator in your family car. Chances are, if it’s a well-designed system, it comes up to running temperature fast, and stays there all day, with the needle barely moving at all.

It is here, in the stabilization area,  that the KLR liquid cooling system falls short. You must have noticed that there are days when the needle moves through 30-50% of it’s arc several times during the course of a single ride. You’ve probably seen it dangerously hot at a stoplight, then a few minutes later it’s well below proper operating temperature as you get on the highway in the cool morning air. Sometimes in the winter, it never warms up at all, not allowing the oil to cleanse itself of contaminants or lubricate properly, and not allowing the internal engine components to heat up to proper operating temperature. This may look like the engine is running cool, but actually it’s very bad.

The KLR is unable to control and stabilize the temperature of its engine. Like I said, this is bad. For all the reasons we spoke of above.

Part of the reason it can’t control and stabilize the temperature of the engine is in the poor airflow through the radiator, causing it to run too hot. But we’ve found ways to fix this as was mentioned above.

It’s the lower end of the temperature range that we’ve not been able to control. And as I’ve tried to explain, being too cold is just as dangerous to an engine as being too hot.

The fault here lies in the poorly designed KLR thermostat system.

Ya see, the KLR thermostat has at least two major problems. One is that it opens too soon at about 160-170 degrees, and the second is that there is no bypass around the thermostat to keep the coolant circulating through the engine as it heats up.   The thermostat opening too soon causes the engine to run too cold (especially in winter), and the lack of water circulation causes the water in the top of the engine to get very hot, while the water in the lower part remains stuck there (and cold) until the thermostat opens at about 170 degrees. Then… the hot water rushes out, and the cold water rushes in …and closes the thermostat… until the cycle starts over. I don’t need to tell you how bad this is for the parts in the engine.

What is needed is a method for the water in the engine to keep moving around so it heats up quickly and evenly, and also circulates around the thermostat, so it doesn’t open and then slam closed with each inrush of cool water.