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Changing Antifreeze

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I'd like to change my antifreeze before winter, but I've heard that people have problems with getting the air out of their system on the 4.0's. So my question is is it possible to do this without getting air in the system?


This is probably cheating, but when I first got my MJ I had the coolant replaced, and they used a pressure flush/replacement machine.


No worries.

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Yes, there are problems with changing out the anti-freeze. This is a closed cooling system, and it can get air locked in the block.


Last time I changed out the raditor, I took the top hose off at the thermostate housing, poured the 50/50 anti-freeze into the hose, filling the raditor, and let the air out thru the thermostate housing, added the IIRC 2.5 gallons, and when the anti-freeze started coming out of the housing, put the hose back on, and then added some to the presser bottle, about 1/2 way, left the cap off, started up the truck, let it get to operating temperature, shut off the engine, screwed the cap on the presser bottle, let it cool a good half hour, and it sucked out the anti-freeze out of the pressue bottle, filled it back up to the 1/2 way mark, and never had a problem with it, all summer.

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If you prop up the rear end of the truck higher than the front, you can loosen the temperature sensor in the back/top of the head to let air out and you fill it back up. You might need the engine to be running to get the air to all circulate to that spot so be careful and have someone at the wheel ready to turn off the truck should you accidentally unscrew the sensor too much and it pops off, spraying you with coolant. Safety glasses are a must and it's even better if you have a rag over the sensor as you're working to keep the spray to a minimum.

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