The jeepfan.com 2004 Wrangler TJ Unlimited has almost 195,000 miles on it. Since we have only owned it a short time it’s hard to know its maintenance history and recently we have noticed that the coolant has been boiling in the overflow bottle. Even more recently it boiled so bad that it puked up antifreeze all over the inside of the engine and on the driver side fender. Something needed to be done.
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Often boiling can be a defective radiator cap or a slow thermostat. Since the Jeep wasn’t running too hot but the boil over happens after highway driving we felt it was just smart to replace the cap and the thermostat. As well as give the cooling system a good flush and new antifreeze.
Some Technical Stuff
If the radiator cap can’t maintain the 18 lbs of pressure the coolant will boil at a lower temperature than the cooling system runs at. When it’s boiling it can create bubbles within the coolant as well as push coolant out of the overflow bottle.
A defective thermostat can cause overheating issues or underheating issues. Defective thermostats often get stuck open or closed, they can additionally become slow to react.
Replacing either or both of these components isn’t expensive and doesn’t take much time.
Parts and Supply List
The recommendation of antifreeze is the G-05 but many other types can be used including the plain green stuff. A good flush is needed if you are changing types since mixing two types together can cause issues. We went with the recommended G-05 antifreeze from Xerex. A new cap and thermostat was used along with a few replacement hoses and clamps.
Draining
With the Jeep’s engine cool remove the radiator cap and open the drain valve on the passenger side of the bottom of the radiator. Collect the old antifreeze for proper disposal, allow the system time to drain.
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We also removed the overflow bottle to drain and rinse it thoroughly. Pull the hose off the fill hole and pry the bottle upward. It will pop up and remove reasonably easy.
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