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post #11 of 16 Old 10-10-2019, 08:26 AM
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Originally Posted by GoMotor View Post
I may need educating on BURPing the cooling system. It seems to me that any air in the system will naturally flow up to the radiator and be trapped there. Then just opening the radiator cap to check the coolant level and adding coolant if necessary should automatically remove all air from the system.

I keep hearing about BURPing, but don't see the need for any special procedure on a KLR. Perhaps the term BURP just means topping off the radiator.
A trapped air pocket in the cooling system can cause turbulence, or other obstacle(s), to full coolant circulation and . . . engine cooling.

Had coolant drained and changed on KLR250; got excessively high temperature gauge readings at low rpm; higher rpm and air speed, not so much. Became frustrated; installed MANUAL FAN SWITCH; could keep temperature down somewhat by liberal engagement of the switch, but . . . "burped," as described above, and hereafter manual fan switch became superfluous, redundant to thermal switch in bottom of radiator.

So . . . in my limited experience, trapped air in the cooling system will not dissipate on its own with the radiator cap closed, and system pressurized.

YMMV!

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre
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post #12 of 16 Old 10-10-2019, 11:05 AM
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Quote:
Originally Posted by Damocles View Post
A trapped air pocket in the cooling system can cause turbulence, or other obstacle(s), to full coolant circulation and . . . engine cooling.

Had coolant drained and changed on KLR250; got excessively high temperature gauge readings at low rpm; higher rpm and air speed, not so much. Became frustrated; installed MANUAL FAN SWITCH; could keep temperature down somewhat by liberal engagement of the switch, but . . . "burped," as described above, and hereafter manual fan switch became superfluous, redundant to thermal switch in bottom of radiator.

So . . . in my limited experience, trapped air in the cooling system will not dissipate on its own with the radiator cap closed, and system pressurized.

YMMV!
I wonder what others may think on this topic. It seems to me that a hypothetical air bubble would flow through the system to the radiator (high point) the same with 0, 5, 10, 15......... pounds of pressure on both sides of it. With the cap on or off.
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post #13 of 16 Old 10-10-2019, 11:49 AM
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Originally Posted by GoMotor View Post
I wonder what others may think on this topic. It seems to me that a hypothetical air bubble would flow through the system to the radiator (high point) the same with 0, 5, 10, 15......... pounds of pressure on both sides of it. With the cap on or off.
I join everyone in respecting the thoughts of other forum members on the subject of burping radiators! I can only share my own limited experience and (perhaps questionable) perception!

You said you wanted to be, "educated" on the subject. Don't want to be pedantic, but . . . conventional wisdom recognizes the merit and value of radiator burping to considerable extend. Thus, I share one of many links found on Google discussing the phenomenon.


Regardless, your hypothesis ("It seems to me that a hypothetical air bubble would flow through the system to the radiator (high point) the same with 0, 5, 10, 15......... pounds of pressure on both sides of it. With the cap on or off.") may be quite valid, regardless of the entries on the subject of radiator burping found on the Internet.

And, finally . . . YMMV!

--------------------------------------

Bonus: This link may explain more fully the conditions wanting burping:

http://automotivemileposts.com/garage/v2n15.html

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre

Last edited by Damocles; 10-10-2019 at 11:52 AM.
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post #14 of 16 Old 10-10-2019, 12:16 PM
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Quote:
Originally Posted by GoMotor View Post
I wonder what others may think on this topic. It seems to me that a hypothetical air bubble would flow through the system to the radiator (high point) the same with 0, 5, 10, 15......... pounds of pressure on both sides of it. With the cap on or off.
On a KLR it normally would, IME.

Some cooling systems on other models and other brands and automobiles have air bleed screws at air trap points in their systems. Sometimes right on top of the thermostat housing. I've even seen air bleeders clear down low, on top of coolant pump housings.
My KX500 has an air bleed at the rear of the cylinder head, because the hose comes off the front of the head & the engine sits at about a 15 degree incline.

The side mounted thermostat on the KLRs and using center stands vs side stands during cooling system re-filling might affect the volume of air that needs to be 'burped'. Improperly locating the air vent hole of thermostat may affect purging of air in the system.
The initial start-up after cooling system re-filling is usually suggested to be performed with the radiator cap still Un-Installed.
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post #15 of 16 Old 10-10-2019, 12:41 PM
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I think that Jeep in that video would have benefited from an air bleed fitting installed in that high arched top hose.

I have my doubts as to whether or not all the air could ever be purged from that system, in that manner. It would take a whole lot steeper up-hill / side-hill to get the top RH radiator hose fitting inlet higher than that arch over the alternator.

One of our past active, very knowledgeable members explained the reduction of cooling system efficiency with entrained (trapped) air emulsified (mixed) into to coolant.

{[QUOTE=Normk;377930]In discussion on another site regarding installing a second radiator, the owner was intending not to use an overflow tank which surprised me.

Problems occur if the radiator is not refilled because the air pulled into the radiator during cooling/contraction will mix into the coolant. As a rule of thumb, 2% entrained air by volume will reduce cooling effect by 8%. 4% trapped air by volume reduces cooling by 38%.

Thought it might be of interest.[/QUOTE)
I did Not know, that the effect was that pronounced!
Thanks Norm.

Almost negates the benefit of the second radiator, considering minus 38% of Both Radiators, doesn't it.}


A pinched radiator vent hose to the recovery bottle or a heat collapsed nipple on the recovery bottle would cause air to become trapped in the radiator!
MandaPanda415, you might check this hose & recovery nipple to confirm that it is not blocked.

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Last edited by pdwestman; 10-10-2019 at 12:45 PM.
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post #16 of 16 Old 10-10-2019, 02:42 PM
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Originally Posted by pdwestman View Post
The initial start-up after cooling system re-filling is usually suggested to be performed with the radiator cap still Un-Installed.
True enough!

From the link posted above:

--------------------------------------------------

In essence, you want to "burp" your cooling system to remove the trapped air. Start with a cold engine. Remove the radiator cap and fill it to the recommended level with a 50/50 mixture of antifreeze and water. Make sure any auxiliary tanks are also at the proper cold fill level. With the radiator cap off, start the engine.. You want 100% circulation of the coolant.

Let the engine operate long enough to warm up enough to reduce the idle speed to a normal idle.

Let it idle until it's at normal operating temperature, keeping an eye on the temperature gauge or light. Do not let your [engine] overheat! Overheating can cause additional problems, such as blowing your head gasket, even warping your carburetor. Once the thermostat begins to open, it's also very important to not rev the engine, even slightly, as this will force coolant out of the open radiator.

You might notice some bubbling of coolant out of the open radiator during warm up. This bubbling is normal if you have air trapped in your system, and is caused by the air escaping as it reaches the area of the open radiator cap. Unless the bubbling is excessive, continue to let the engine run at idle for a few minutes once it reaches normal operating temperature, then shut it down. Allow the engine and cooling system to cool off, preferably overnight. Then check your coolant level again. If it dropped, that means you've displaced some of the air in your system. Refill to proper levels, and repeat the process. Do this until the level doesn't drop any longer, then replace your radiator cap and check your coolant levels at least monthly, or weekly during hot weather.

---------------------------------

Granted, this procedure is NOT KLR650-specific, nor even motorcycle-specific; the instructions remain broad, intended for liquid-cooled engines in general; one might not need to go through all the steps mentioned on a KLR650.

An un-capped radiator fill nozzle allows trapped air escapement from the coolant and cooling system.

“You better put down that gun. You got two ways to go, put it down or use it. Even if you tie me, you’re gonna be dead.” "John Russell" (Paul Newman), Hombre
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