Coolant refill procedure?

Woodrow

Woodrow

1997
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What’s the correct way to refill the coolant in a 4L after draining?

More specifically, how do you get out the air preventing the engine from taking all of its coolant with a closed thermostat? When I’ve refilled after doing something requiring drainage, my radiator will be full when the system still needs a gallon or a little more. Simply running the motor briefly doesn’t clear the airlock. I need to get it warm enough at idle to open the thermostat and then the airlock clears but also the coolant is hot enough to boil. This seems like a disaster waiting to happen as air locked parts of the block and/or head are probably overheating and I worry about warped or cracked parts.

As I’m writing this, I’m wondering if separating a hose at the thermostat housing while filling would work. I am using a non-fail safe (Mopar) thermostat with a bleed hole positioned up.
 
All I ever did to every vehicle I've owned is open the radiator cap and pour it in. Did it two different times so far on my TJ.

The only vehicle I had air associated problems with was a diesel VW Rabbit from the early 80s. IIRC it's radiator had no cap and there was a specific name for the system and how it worked but I just yelled swear words while trying to get it filled. I also believe that the early XJs had a similar system.
 
Edit: I found this in an old thread and it makes sense:

RaymondT​

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If you do decide to drain the block, pop out the temp sensor on the thermostat housing. Pour your coolant mixture into the rad until it starts to burble out the hole for the sensor. Then slap it in, connect the pigtail, and finish topping up the rad.

Removing this sensor allows the block to fill without the system air-locking. It helps to pre-treat the threads of the sensor with pipe thread sealant before you start pouring so it's ready to go.
 
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I top off the radiator, then squeeze the lower radiator hose to push air out and top off with coolant several times. Then fill the overflow bottle to the "hot" level. After a few heat and cool cycles I check the overflow bottle again add coolant as necessary.
 
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Woodrow said:
What’s the correct way to refill the coolant in a 4L after draining?

More specifically, how do you get out the air preventing the engine from taking all of its coolant with a closed thermostat? When I’ve refilled after doing something requiring drainage, my radiator will be full when the system still needs a gallon or a little more. Simply running the motor briefly doesn’t clear the airlock. I need to get it warm enough at idle to open the thermostat and then the airlock clears but also the coolant is hot enough to boil. This seems like a disaster waiting to happen as air locked parts of the block and/or head are probably overheating and I worry about warped or cracked parts.

As I’m writing this, I’m wondering if separating a hose at the thermostat housing while filling would work. I am using a non-fail safe (Mopar) thermostat with a bleed hole positioned up.
Click to expand...

Jerry posted something on here that I used and basically I ran the engine and put a hose in the top and drained coolant until it was just water coming out then stopped filling with water and let it drain, then topped off with coolant in the radiator. No issues with anything since the cap should allow itself to burp on its own
 
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