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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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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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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.
 

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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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Discussion Starter #5
Thanks for the responses iride4u and Damocles. I did not burp the system...guessing that's it.
 

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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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Discussion Starter #7
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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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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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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"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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My present bike has a PO installed indicator light for the fan, which is mounted in place of the blanked indicator light position. I did a conversion to my previous KLR which placed the indicator into that location but used a colored lens which made it look like stock. Can't recall at all what was done....memories, from the corners of my mind...gone somewhere.

My older son was chucking over one of my old age mental lapses until I pointed out that when he does something like that it's quite amusing to me. When I do something like that, however, he's looking at heredity. He's not quite so smug now.... ;-)
 

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My jewel is connected between the fan power lead (BLUE) and frame ground; it is NOT connected directly to the manual switch.

When the jewel lights, power is being applied to the fan motor; otherwise, the bulb might show only the switch position. The hookup shown involves thermal switch (or manual switch) condition, and fan relay status, when bulb is ON.
 

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My quick view of the coolant flow path in my gen2 KLRs is that the radiator is higher than the pump, tubing, cylinder, head and thermostat, so by filling the radiator gravity flow will purge and fill the entire system if given time to do so. The time factor is due to the small bleed hole in the thermostat. A clogged bleed hole can cause filling problems. Under normal circumstances filling fully is very easy. Just fill the radiator, leave the cap off, start the engine and wait to see coolant entering the top of the radiator from the return hose. Then top off the radiator and you are done.

I have not tried to reverse the hose connections at the pump and don't know if it can be done, but if they were reversed, cool water from the radiator would be fed backwards through the thermostat bleed hole and the thermostat would not get hot and would not open causing over heating.
 

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Under normal circumstances filling fully is very easy. Just fill the radiator, leave the cap off, start the engine and wait to see coolant entering the top of the radiator from the return hose. Then top off the radiator and you are done.
+ 1!

I consider this process (including the radiator-cap-off waiting period, insuring the thermostat has opened and the coolant circulates to free any air mass), "burping."

While generally, water seeks its level and gravity would expel air pockets, some "inverted 'U'" passages and galleries may exist in the hydraulic circuit, where air can be trapped (if no burping is done) and inhibit coolant circulation at idle.

I agree with you, GoMotor. My recommendation and advice upon re-filling coolant: Burp.
 

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It's a good idea to capture the coolant drained in order to estimate the amount which should go back into the system. Not rocket science but it will make it obvious when there is a large amount of air trapped in the system.

As as been said, KLR650's are usually not a problem to fill.

It is quite easy to reverse the water pump hoses as have seen at least two with the hoses in the wrong orientation. The last one was last year and had apparently been that way for some time without apparent effects. Yes, I'm surprised but neither bike had a T-Bob or other by-pass system.

If one considers the normal flow: water pump to base of cylinder, through cylinder coolant jacket to head coolant passages, then into the thermostat pocket. One will notice that there will be a small flow of coolant through the vent slot in the thermostat. "Small" is relative because 60 PSI can move quite a lot of coolant through that slot.

This small flow should take air through and to the radiator since the radiator is "up hill" . Coolant flows to the radiator top, down through the radiator and to the water pump.

When the temperature in the thermostat pocket exceeds thermostat opening temperature, the thermostat will open and full flow will circulate until such time as the thermostat closes due to reduced coolant temperature.

With water pump hoses reversed, coolant flows from the water pump, upward top and through the radiator and "down" to the thermostat housing by way of the upper radiator hose. Coolant flow must be smaller in this direction because:
1) The thermostat is closed as before and flow is restricted to that through the vent slot.
2) Water pump pressure cannot exceed the radiator cap pressure of 1.1 atmospheres or about 16 1/4 PSI. If the pressure exceeds this level there should be venting of coolant from the radiator cap to the over flow tank.

Conditions should prevail until the heat in the thermostat pocket reaches thermostat opening temperature at which point coolant will circulate (in reverse) until the thermostat closes. I expect the thermostat will close much more rapidly in this flow direction since cooler coolant enters from the radiator rather than warmer coolant from lower down in the engine.

I'd expect the thermostat to cycle much more frequently and that over heating would be likely, combined with venting to the over flow during any but low RPM.

That this didn't happen with the last one I saw is a bit of a mystery which simply shows that the cooling system does not perform exactly as my impressions predict. Automotive engines having a reverse rotation water pump accidentally installed always over heated, IME. Mustangs, for example which had a "V" belt water pump installed onto a serpentine application or vice versa, for example.

Interesting but haven't been interested enough to repeat the test in warmer weather or on my own bike.
 

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Discussion Starter #16
Finally got some time to devote to the bike today and thought I'd have this all done. Reused the water pump cover gasket which was still in one piece and appeared ok. Unfortunately, it wasn't. As I started the burping process, coolant started leaking at the water pump cover. Guess that's how things go sometime and you learn lessons...another gasket already on the way.
 
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