Cooling Issue - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 16 Old 08-17-2014, 05:01 PM Thread Starter
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Cooling Issue

I replaced the water pump seal on my KLR and put everything back together last night. Today, I rolled it out and fired it up. The thing started to overheat, spit antifreeze out the back hose and cooling fan didn't come on. I haven't put many mile on the bike but when I did ride it last, the temp needle went past mid point but not much and the cooling fan did turn on. Any thoughts? Did I possibly bind something up with impeller? I was careful to install all the washers as they came off and torqued everything to spec.
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post #2 of 16 Old 08-17-2014, 05:26 PM Thread Starter
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Just pulled the water pump cover and impeller back off...everything looks clean. The radiator felt cool as opposed to the engine block and the coolant level didn't go down at all from where I topped it off in the plastic tank. Could this be a thermostat issue?
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post #3 of 16 Old 08-17-2014, 10:14 PM
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If you did not fill the cooling system up all the way you could have air bubbles. I do not have a manual for the KLR handy but on my BMW K1600 there is a procedure that must be followed.

2014 KLR650 New Edition
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post #4 of 16 Old 08-17-2014, 11:54 PM
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Did you BURP your cooling system?

To burp, you must fill your radiator with coolant; run the engine WITH THE RADIATOR CAP OFF, 'til the coolant begins to circulate (i.e., 'til the thermostat opens); give the system time enough to expel the air bubbles from the open radiator port . . .

Then, shut her down; when reasonably cool, top off radiator and reservoir.

Eliminate air bubbles in cooling sytem; air bubbles frustrate cooling; coolant temperature at cylinder head can be ski high (that's the temperature the gauge reads), while the thermal switch in the bootom of the radiator (the device controlling the cooling fan) thinks it's just a nice day, only pleasantly warm . . . Air bubbles sometimes inhibit circulation; thus . . . burping remains essential, for a fully-functional cooling system.
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post #5 of 16 Old 08-18-2014, 09:01 AM Thread Starter
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Thanks for the responses iride4u and Damocles. I did not burp the system...guessing that's it.
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post #6 of 16 Old 08-18-2014, 01:29 PM
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The stock KLR thermostat (160 F) has a decent sized slot to act as an air bleed during filling and to provide some circulation when thermostat is closed. Generally this will allow the air to clear the system but, as Damocles recommended, burping the air from the system needs to be considered.

A bit of sludge can restrict the slot or someone may have installed the thermostat with slot down which leaves more air in the head. I want to repeat what he said that air can be trapped in the cylinder head because over heating of the exhaust valve area can occur to a very high degree despite the temperature gauge reflecting a lower reading.

The radiator fan only comes on when the coolant exiting the radiator exceeds about 210 F which means the thermostat must be open for circulation, and the temperature be above 210 F. The cooling fan's operation confirms that the thermostat has reached temperature and is wide open. In this state air will be forced out of the engine into the radiator and should purge.

If the coolant level is very low, the water pump will not be effective and so not be capable of forcing the coolant lower in the engine to pass through the thermostat bleed hole. This can lead to having the engine almost full of coolant but the water pump unable to build enough pressure to force the air pocket around the thermostat out. In this condition the thermostat would be dependent on heat transfer through the air pocket which often seems not to be sufficient to heat the thermostat. A partially blocked thermostat hole makes this worse because the coolant cannot equalize level.

The pump should fill with coolant added to the radiator because it's a down hill run but some engines can be very difficult. Many modern engines have air bleeds or a prescribed hose removal procedure to burp air. One has not lived until one has burped the air from my 1986 Toyota MR2 for example.

When the water pump is full of coolant and engine rev'd up the pressure against a closed thermostat can reach 60 PSI which shoots coolant through the thermostat hole at a great rate and will purge air almost instantly. If the system can't generate significant pressure, it may not purge the air.

Sometimes people "chicken out" before the thermostat would have opened but I'm often in that camp as can only speculate as to how high the temperature might reach in some pockets.

As Damocles stated, shutting down for a short "rest period" can allow the heat in the head time to even out and to heat the thermostat without over heating some areas.

It's good practice, IME, to measure the amount of coolant drained as a guide to how close to full is the refill. The KLR is not a tough one to clear the air and haven't heard of one damaged by partial refill so wouldn't worry in that regards.
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post #7 of 16 Old 08-19-2014, 07:03 AM Thread Starter
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Thanks Normk...that's definitely some more useful info. Just waiting for some free time to get back to the KLR
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post #8 of 16 Old 08-19-2014, 07:43 AM
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Quote:
Originally Posted by Normk View Post
The KLR is not a tough one to clear the air and haven't heard of one damaged by partial refill so wouldn't worry in that regards.
KLR250 story: Coolant was drained and replaced by a dealership shop on an extended-service maintenance episode.

Later, I found the temperature gauge reading dangerously high when idling in hot weather, but . . . the fan didn't kick in. At speed, and at higher rpm, not a problem; engine temperature normal.

I feared a defective thermal switch; rigged up a manual fan switch and indicator light.

Then, when the temperature gauge needle climbed high during a protracted idle, I flipped the switch, activating the fan. Although the fan operated,, the temperature did not go down!

Problem: AIR BUBBLE. After properly burping the cooling system, no more high cylinder head coolant temperature without fan activation. The air bubble apparently comprised a barrier to coolant circulation at idle, preventing transfer of the high cylinder head coolant temperature to the thermal switch in the bottom of the radiator.

Moral of the story: Burp well your cooling system (lest ye come to grief).

Oh, the manual switch and indicator? Still got 'em; consider the switch, "an elegant solution to a non-existent problem," if a functioning thermal switch is in the circuit, but . . . the jewel indicator light is GREAT; shows whenever the fan comes on, confirms maximum cooling when needed.
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post #9 of 16 Old 08-19-2014, 10:11 AM
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Damocles posted: "Oh, the manual switch and indicator? Still got 'em; consider the switch, "an elegant solution to a non-existent problem," if a functioning thermal switch is in the circuit, but . . . the jewel indicator light is GREAT; shows whenever the fan comes on, confirms maximum cooling when needed."


Excellent way to describe the modification. I've done it also, mostly because I could and wanted to play with the system. :-)
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post #10 of 16 Old 08-19-2014, 10:46 AM
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"Automatic" operation; lower coolant temperature less than 210 degrees F.:



Manually-activated fan:



When switch is in AUTO position, jewel indicator light shows when fan is activated by thermal switch.

NOTE: KLR250 fan circuitry operationally identical to Generation 1 KLR650; Generation 2 KLR650? Somewhat different; don't have no stinkin' fan relay!
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