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2005 KLR650
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I'll disagree with that statement.
The engine metals are perfectly safe up to 300-350F+ as long as the engine oil stays below about 250-275F in the sump.
Most air-cooled motorcycle engines operate in the 275-350F cylinder head temp range very frequently.
Liquid-cooled engines need pressurized Coolant/Antifreeze to stay below the boiling point of the coolant, to prevent hot spots from developing. Once any hot spot develops the whole system can spike quite quickly.


I'll disagree with that statement also.
A 165F thermostat can not compensate for too small of radiator or too slow (or too fast) of coolant flow or too slow of air flow, be it in a KLR or any hot-rodded engine!
The engine metals are fine. The issue is when you have different chunks of metal at different temperatures. This is particularly problematic when the chunks of metal have different thermal expansion properties, like an aluminum head on a cast iron block. The two chunks of metal expand at different rates, and either one of them warps, or the gasket can't handle the slip between them.

I'm not as familiar with air cooled engines. Not my specialty :) But I could see them running hotter by default and caring less because there aren't coolant passages in the head gasket.

I didn't say 165F thermostats would fix a inadequate cooling situation. I just said it was an old hot rodder solution which gives some extra overhead before the engine overheats. It won't cure a constant overheat issue under normal running conditions.
 

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I just said it was an old hot rodder solution which gives some extra overhead before the engine overheats. It won't cure a constant overheat issue under normal running conditions.
Sort of what they're doing with a top fuel engine that doesn't even have a cooling system - using the entire block and head as a giant heat sink over brief periods of intense operation.
 

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The temp gauge is the only "high tech" item on the entire bike. Why would you want to get rid of it?

KLR doesn't even have a master warning/idiot light.

Kawasaki brand bikes are notorious for weak prone to fail stators.

My old low tech Versys 650 had an idiot light. Without that light I would have had no idea that my stator had failed until the bike quit running. As it worked out I was able to make it to the next town and call for help. Had I continued my planned route I would have turned into a F O R D in a remote area with no cell coverage.
Art Painting Rectangle Drawing Illustration
 

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I don't know about that. One day when I was riding in 105F heat, my fan blew a fuse. I didn't know about it until I glanced down at my temp gauge and saw that the needle had risen to the red. (Gen 1)

It was a bit of a joke; I like my temp gauge and wouldn't want to lose it.......but at the same time I can easily see why Kawi would do away with it; how many posts do we get about KLR's overheating when they are just running normally? .....I've answered way too many of those posts here and elsewhere.


Dave
 

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I didn't say 165F thermostats would fix a inadequate cooling situation. I just said it was an old hot rodder solution which gives some extra overhead before the engine overheats.
Neither a 195F nor a 165F thermostat will give any "extra overhead before the engine overheats"! 165F isn't even hot yet.
195F is still not up to the boiling point of water only, even without a pressure cap!

Only a larger radiator or more efficient radiator or more cooling air flow can give "extra cooling capacity" to prevent overheating.

The Gen 1 radiator was almost too small, the Gen 2 & Gen 3 radiators are larger, much more efficient & more easily damaged.
 

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It could easily be my mechanical ignorance, but some of the posts in this thread, particularly those mentioning "over-cooling" and "operating temperature" see to imply that the stock 165F thermostat is going to determine the temperature of the coolant in the cooling system. Isn't this just the temperature at which the thermostat is supposed to open and let coolant from the radiator into the block? If so, it seems like this thermostat is only going to allow coolant to flow through the block earlier than a 195F thermostat, but it doesn't determine fully-warm operating temperature, i.e. coolant may begin to flow through the block at 165F, but the coolant temperature will continue to increase as the bike continues to warm up.
 

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'08 KLR
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It could easily be my mechanical ignorance, but some of the posts in this thread, particularly those mentioning "over-cooling" and "operating temperature" see to imply that the stock 165F thermostat is going to determine the temperature of the coolant in the cooling system. Isn't this just the temperature at which the thermostat is supposed to open and let coolant from the radiator into the block? If so, it seems like this thermostat is only going to allow coolant to flow through the block earlier than a 195F thermostat, but it doesn't determine fully-warm operating temperature, i.e. coolant may begin to flow through the block at 165F, but the coolant temperature will continue to increase as the bike continues to warm up.
Actually, the thermostat controls the temperature at which coolant can flow out of the block so for all practical purposes, it sets the max engine temperature. The only way the temp will rise above that is if the radiator has too little surface area to shed heat at the same rate the engine is making it, given ambient temps and the amount of/speed at which air is flowing past the cooling fins. Additionally, in a simple, basic cooling system like a KLR, the actual average internal coolant temperature will be somewhat cooler than that and will include fairly severe and abrupt downward swings followed by a slow climb back to thermostat temp because, without a bypass, when the thermostat does open the coolant that enters at the bottom of the block is 100% from the radiator, which has just been sitting there not moving since the last time the thermostat opened and may have called off by 30, 40, or even 50° or more. The delta between the coolant temp leaving the motor and the coolant temp flowing in will tend to be larger under cooler ambient temps and lower engine loads - colder air removes more heat, and lower engine loads extend the periods between thermostat openings, giving more time to cool. Not incidentally, this is the issue that the Ther-O-Bob seeks (and largely succeeds) to address. It won't raise or reduce max coolant temp, the thermostat still does that. What the 'Bob does do, with its bypass system, is reduce the coolant temperature delta (difference in temp between coolant input and output), making for an engine that runs at a consistent temp, or at least within a much smaller range.
 

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Neither a 195F nor a 165F thermostat will give any "extra overhead before the engine overheats"! 165F isn't even hot yet.
195F is still not up to the boiling point of water only, even without a pressure cap!

Only a larger radiator or more efficient radiator or more cooling air flow can give "extra cooling capacity" to prevent overheating.

The Gen 1 radiator was almost too small, the Gen 2 & Gen 3 radiators are larger, much more efficient & more easily damaged.
You’re confusing dynamic cooling capacity of a cooling system, which is a function of how fast the system can move heat from the engine to the air, with thermal capacity of the coolant in the system, which is a function of the physical properties of the coolant and the volume of coolant.

It takes X energy to heat coolant by 1deg. If you have a cooling system that is running at 165F, it will take more thermal energy to get it to 230F than it will take the same system running at 195F to get to 230F.

If the cooling system is adequate to regulate temperature under mild load conditions, but inadequate under heavy load or high ambient heat conditions (this describes most pre-70s vehicles), you might be able to buy yourself a couple more minute of high load operation before the engine overheats by running a 165F thermostat. It won't change the fact that the engine will overheat, because that's up to the cooling capacity of the system, but that's often enough to get you back from the end of a drag strip, or up to the top of the grade you're trying to climb.
 

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Actually, the thermostat controls the temperature at which coolant can flow out of the block so for all practical purposes, it sets the max engine temperature. The only way the temp will rise above that is if the radiator has too little surface area to shed heat at the same rate the engine is making it, given ambient temps and the amount of/speed at which air is flowing past the cooling fins. Additionally, in a simple, basic cooling system like a KLR, the actual average internal coolant temperature will be somewhat cooler than that and will include fairly severe and abrupt downward swings followed by a slow climb back to thermostat temp because, without a bypass, when the thermostat does open the coolant that enters at the bottom of the block is 100% from the radiator, which has just been sitting there not moving since the last time the thermostat opened and may have called off by 30, 40, or even 50° or more. The delta between the coolant temp leaving the motor and the coolant temp flowing in will tend to be larger under cooler ambient temps and lower engine loads - colder air removes more heat, and lower engine loads extend the periods between thermostat openings, giving more time to cool. Not incidentally, this is the issue that the Ther-O-Bob seeks (and largely succeeds) to address. It won't raise or reduce max coolant temp, the thermostat still does that. What the 'Bob does do, with its bypass system, is reduce the coolant temperature delta (difference in temp between coolant input and output), making for an engine that runs at a consistent temp, or at least within a much smaller range.
So the thermostat will open when coolant in the block reaches 165F, but that's the only limit associated with the thermostat, meaning the coolant temperature can climb from there without reaction from the thermostat. So the stock operating temperature of the KLR varies to either side of 165F regularly, causing the thermostat to cycle between opened and closed? I might argue that because the Tbob includes a 30F higher thermostat, it does raise the max coolant temperature particularly under cold-weather driving conditions because as you said, the thermostat does that. Having looked at Watt-Man's documentation, I deleted some of my earlier ignorance from this post and I see that with the Tbob, operating temp is indeed ~30F higher out of the top of the block and temperature differential between top/bottom of the block is reduced to ~20F from ~40-60F, if his data is to be trusted.
 

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So the thermostat will open when coolant in the block reaches 165F, but that's the only limit associated with the thermostat, meaning the coolant temperature can climb from there without reaction from the thermostat. I thought I read somewhere (sorry, can't remember where, maybe in a KLRforum thread) that the Tbob only increases fully warm operating temperature approximately 5F but that temperature is possibly 30-40F above 165F. If that's true, the thermostat still does nothing more to affect operating temperature after it has opened. Are you implying that the stock operating temperature of the KLR varies to either side of 165F regularly, causing the thermostat to cycle between opened and closed?
Yes. The thermostat in every water cooled internal combustion engine that operates using a wax capsule (which is every engine coolant thermostat that I'm aware of) is in an open or closed state, there is no variable attenuation. In a modern vehicle, where a computer is monitoring or controlling every variable of engine input and operating conditions, they probably could put in a computer controlled gate that would read ambient temp, fuel input, engine load, speed, etc., and compute how far to open the gate to provide just the right amount of coolant flow - and I wouldn't be surprised to find out that such systems exist on exotic, close tollerance, high powered engines such as you find in F1 cars - but thats a lot of complexity and cost for no real gain in vehicles for which a standard thermostat and a properly engineered bypass system have proven more than accurate.
 

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I appreciate the back and forth on the Tbob though I'm sure it's been kicked around all over the forum before. I'm trying to decide if it's a mod I want, and I'm not sold yet, but this is helpful.
 

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If the day is cold, this cycle will continue all day – and if ridden real smoothly, you’ll eventually hit some steady-state point where the thermostat is just barely open and temperatures stabilize (say, 50° coming in and 158° going out). If it’s a hot day (say 90°) the KLR radiator won’t be able to dump as much heat out of the coolant as the engine is adding, so temperatures will continue to climb past the 158° thermostat rating and the thermostat will be open all the time. Since the heat removed from a radiator is proportional to the difference in the temperatures of the coolant in it and the air around it, temps will continue to climb until the radiator is finally able to dump as much heat as the engine is adding to the coolant. Stock KLR’s seem to stabilize around 110° to 115° over ambient, meaning on a 90° day that coolant exiting the engine stabilizes around 200° to 205°F... and that's if you're not tailgating, climbing a hill, carrying a passenger, or riding fast. Those things would raise temps even higher....

It's all right here: http://watt-man.com/wp-content/uploads/2021/01/Art_TB_Testing.pdf

And: http://watt-man.com/wp-content/uploads/2020/11/KLR_Margin.pdf

The bottom line is that a thermobob raises the minimum temps the engine sees once warmed up; it doesn't raise the maximum temps it could see during use as that's a function of the radiator, coolant, water pump, fan, etc.
 

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Stock KLR’s seem to stabilize around 110° to 115° over ambient, meaning on a 90° day that coolant exiting the engine stabilizes around 200° to 205°F
So you'd have to be riding in below ~50F ambient temperature before the stock thermostat cycling would potentially commence after warm-up. Has the stock thermostat changed since Watt-Man's write-up to 165 from 158?
 

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I appreciate the back and forth on the Tbob though I'm sure it's been kicked around all over the forum before. I'm trying to decide if it's a mod I want, and I'm not sold yet, but this is helpful.
Here's an animation on YouTube that shows how a thermostat in a cooling system with a proper bypass opens and closes to redirect water. It doesnt explain the 'hows' of a wax capsule thermostat, but you can find that here if you're curious.
 

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So the thermostat will open when coolant in the block reaches 165F, but that's the only limit associated with the thermostat, meaning the coolant temperature can climb from there without reaction from the thermostat. So the stock operating temperature of the KLR varies to either side of 165F regularly, causing the thermostat to cycle between opened and closed? I might argue that because the Tbob includes a 30F higher thermostat, it does raise the max coolant temperature particularly under cold-weather driving conditions because as you said, the thermostat does that. Having looked at Watt-Man's documentation, I deleted some of my earlier ignorance from this post and I see that with the Tbob, operating temp is indeed ~30F higher out of the top of the block and temperature differential between top/bottom of the block is reduced to ~20F from ~40-60F, if his data is to be trusted.
A picture is worth a thousand words. A picture with text is even better.
 

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I appreciate the back and forth on the Tbob though I'm sure it's been kicked around all over the forum before. I'm trying to decide if it's a mod I want, and I'm not sold yet, but this is helpful.
I think you’ll find on this forum that “agreeing to disagree” and “it’s your bike, ride it/mod it however makes you smile” is typically the rule of the day😉.
 

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Actually, the thermostat controls the temperature at which coolant can flow out of the block so for all practical purposes, it sets the max engine temperature.
That part of your statement is incorrect. The thermostat attempts to control the Minimum operating temperature.



If the cooling system is adequate to regulate temperature under mild load conditions, but inadequate under heavy load or high ambient heat conditions (this describes most pre-70s vehicles), you might be able to buy yourself a couple more minute of high load operation before the engine overheats by running a 165F thermostat. It won't change the fact that the engine will overheat, because that's up to the cooling capacity of the system, but that's often enough to get you back from the end of a drag strip, or up to the top of the grade you're trying to climb.
The KLR's with temperature Gauges and stock & standard cooling systems (including the 157 -162F rated thermostat) will roll down the open highway all day long in 60-80 F ambient air temps with the temp needle hovering at about 1/4 scale (160'ish).
But when one rolls into town and has to stop for a mere minute or two at the first stop light the temp gauge will invariably climb right up to at or slightly above 1/2 scale (210'ish). Then the fan turns on & off and basically keeps the coolant hovering at its switch set points of 214-189F (and this is at the Bottom of the radiator, not temp gauge sender).

One could install a Thermo-Bob and use the OEM 160F thermostat and it would warm-up Quicker in the morning & remain more stable on the gauge in those first 20-30 minutes of operation. But rolling into town & being stopped at the first stop light it would still climb to the cooling fan set point as described above.
With a 195F thermostat installed the engine would simply not chill back down to 160F upon regaining sufficient road speed which cools the radiator & its fan switch.

Again, a 160F thermostat can not give any real advantage to reduction of possible over-heating (260F+) in these KLR engines. That is controlled by radiator size, coolant flow speed & air flow speed. The increased radiator size of the Gen 2 & 3's ensures that.
If you are climbing a mountain pass & the thermostat is wide open & the cooling fan is running because the bottom of the radiator is above thermostat temp, correct. Doesn't matter which thermostat is installed from that temp up, the engine will either stabilize at a higher temp, continue to heat, or cool down after load is reduced. Neither system is too hot until 260+F.


The thermostat in every water cooled internal combustion engine that operates using a wax capsule (which is every engine coolant thermostat that I'm aware of) is in an open or closed state, there is no variable attenuation.
I'll say that is incorrect.
I'll suggest that you ought to dangle a thermostat & a thermometer into a kettle of Coolant/Antifreeze and watch how slowly & gradually the wax capsule attains fully open or fully closed. The temp number on them is simply the beginning of opening (+/- a few degrees). They are perfectly happy to operate in partial open position if they receive Steady temp coolant which is what the Thermo-Bob provides.
 

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Am I wrong? Ultimately the thermostat opens when it is to the correct operating temp and closes if it gets a little cold. Doesn't that mean it is at a proper operating temp? I assume at 40 degrees, it should get at least the 160 degrees.

Growing up in an area where it would hit the -20F in the winter, we would block part of the radiator so the inside of the car would warm up faster and MAYBE get a little warmer. If you didn't use that wind block, the car never seemed to suffer. You just may have had to wait an extra couple miles before you got any real heat coming out of your dash.

They use them on Diesels to keep more heat in the engine compartment to prevent your fuel from jelling up and killing the engine in the middle of nowhere. No cell phones back then.
 

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Am I wrong? Ultimately the thermostat opens when it is to the correct operating temp and closes if it gets a little cold. Doesn't that mean it is at a proper operating temp? I assume at 40 degrees, it should get at least the 160 degrees.
Modern (1965+?) proper operating temperature is closer to 195F+, but engine cooling systems NEED to have Radiator Bypass systems to operate Smoothly/Consistently, even with a mere 160F thermostat. Which one could use in the KLR Thermo-Bob, but that partially defeats its benefits.
 
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