coolant bypass - Kawasaki KLR 650 Forum
2008+ KLR650 Wrenching & Mod Questions For repair, maintaining or modifying discussions related to the newly updated 2008 and beyond, Generation 2 KLR650 Motorcycle.

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post #1 of 30 Old 08-16-2018, 10:23 AM Thread Starter
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coolant bypass

I've been reading about the merits of installing a thermo bob. As I understand, one of it's main functions is to bypass coolant around the thermostat to pre-warm the coolant in the radiator, thus preventing the thermo shock of ice cold coolant rushing into already very hot water jackets in the cylinder when the thermostat opens.
My bike may be the exception, but doesn't the bike already bypass coolant when cold? I can start my bike from sitting overnight and within less than 60 seconds the radiator is getting hot. At 1 minute I cant hold the top of the radiator tank or it will begin to burn my hand. Meanwhile, the temp gauge hasn't yet started to move. This leads me to believe the stock KLR is already doing half the function of the thermo -bob. Am I wrong or is there something wrong with my new bike?

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post #2 of 30 Old 08-16-2018, 08:09 PM
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The T Bob works to circulate coolant in the engine cylinder to maintain an evenly heated cylinder, then when the temp rises enough to open the thermostat, coolant flows to the radiator to remove the heat from the coolant. This action mimics car engine cooling systems, at least the older systems I'm familiar with.

I too notice that even with a T Bob, the radiator starts warming almost right away. I contribute this partly to the fact that there is a tiny bypass in the thermostat itself which allows some flow even when the stat is "closed".

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Last edited by dan filipi; 08-16-2018 at 08:12 PM.
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post #3 of 30 Old 08-16-2018, 10:35 PM Thread Starter
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I think I was misunderstanding how the thermo bob worked. I went to Watt Man's site and read the pdf detailing how it works and have come to the conclusion that I need one of these and need one as soon as possible. Fall is coming soon and here in Michigan in stock form this bike will never heat up enough to keep the oil dry. Gotta love the aftermarket and deep thinkers that dream up this stuff. Great price too @ $125 shipped.
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post #4 of 30 Old 08-16-2018, 10:44 PM
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I put the T Bob on about 3,000 miles ago. No cold weather riding yet, but cool nights.
I got the temp gauge overlay from him too and see temps stay pretty consistent 180-190 where before in cooler freeway riding it would drop pretty low on the gauge. Seems like a good thing to have.
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2018 Ducati V4S
1983 GL1100 Goldwing
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post #5 of 30 Old 08-17-2018, 04:23 PM
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Installed the T-Bob last Monday. Running in upper 90's during the day and a low of 56įf this morning. Temp on gauge just rides aft of mid-level. Used to always run at the bottom of the gauge near the low mark.
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post #6 of 30 Old 08-17-2018, 07:48 PM
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Thermobob??

I see where it can get the engine up to temp. quicker, but Just wondering, If you get stuck in traffic, does the TB keep the bike from over heating?

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post #7 of 30 Old 08-17-2018, 08:45 PM
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Quote:
Originally Posted by larry31 View Post
I see where it can get the engine up to temp. quicker, but Just wondering, If you get stuck in traffic, does the TB keep the bike from over heating?
larry31,
It is and always has been the jobs of the Water pump, the Radiator, the Fan and/or Forward Motion to keep a liquid cooled engine from over-heating.

The Thermo-Bobs only 2 duties are to more Quickly bring the engine up to Proper operating temperature of 195-205 (middle of gauges) and help prevent it from dropping below that temp every time you achieve freeway speed.

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post #8 of 30 Old 08-17-2018, 09:01 PM
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I wonder where the misconception came from that the T Bob helps anything run cooler? Iíve seen others online and here mentioning that.
If anything it makes it run warmer....that is, Making it warm up faster, and helping it not to dip down to lower scale of the temp gauge.
Iíve seen mine dip down well below 180 degrees in low 50ís riding even with it. Aluminum cylinder and block is a big heat sink after all.

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2017 BMW S1000RR (traded in for
2018 Ducati V4S
1983 GL1100 Goldwing
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post #9 of 30 Old 08-17-2018, 09:20 PM
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Quote:
Originally Posted by dan filipi View Post
I wonder where the misconception came from that the T Bob helps anything run cooler? Iíve seen others online and here mentioning that.
If anything it makes it run warmer....that is, Making it warm up faster, and helping it not to dip down to lower scale of the temp gauge.
Iíve seen mine dip down well below 180 degrees in low 50ís riding even with it. Aluminum cylinder and block is a big heat sink after all.
The KLR650's have always struggled to maintain half-way on the gauge in the winter or cooler climates, because of the 160 thermostat.

The Thermo-Bob was originally designed during the Gen 1 days. With the smaller radiator the Gen 1 will generally operate at about 3/4 to 7/8th scale on the temp gauge in summer temps.
The Thermo-Bobs inventer / seller is from Phoenix AZ, so too many people just make the wrong assumption.

They never read ALL of the information on the sellers web-site. He does have information to help keep the Gen 1 KLR's below the 7/8th scale of the temp gauge, so they get easily confused as to the Thermo-Bobs true purpose.
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post #10 of 30 Old 08-18-2018, 12:33 AM Thread Starter
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Quote:
Originally Posted by pdwestman View Post
The KLR650's have always struggled to maintain half-way on the gauge in the winter or cooler climates, because of the 160 thermostat.

The Thermo-Bob was originally designed during the Gen 1 days. With the smaller radiator the Gen 1 will generally operate at about 3/4 to 7/8th scale on the temp gauge in summer temps.
The Thermo-Bobs inventer / seller is from Phoenix AZ, so too many people just make the wrong assumption.

They never read ALL of the information on the sellers web-site. He does have information to help keep the Gen 1 KLR's below the 7/8th scale of the temp gauge, so they get easily confused as to the Thermo-Bobs true purpose.
I confess to being one of those guys who had only read posts on the forum about it and not educating myself. For all KLR owners not currently running the bypass system I urge you to go to his website and download and read the pdf. it is very in depth in it's explanation of how it works. He tested it with thermocouplers and some fairly sophisticated monitoring equipment in various temps during real world riding conditions. What I got out of it is that it both quickly brings it up to a higher running temp and keeps it closer to a steadier temp than the stock form where the temp jumps up and down like a pogo stick. I have always been taught that oil likes to run hot to keep condensation boiled off and if you run short runs in spring or fall you'll see milky oil under the filler cap because the engine just doesn't get hot enough the way Kawasaki designed it.

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