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Jeep CJ7 Radiator Overflow Tank

Troubleshooting Tips for the Jeep CJ7 Radiator Overflow Tank

Also known as the overflow bottle or reservoir, the radiator overflow tank of the Jeep CJ7 has the dual purpose of storing high-temperature coolant and to allow you to refill the radiator without disrupting its internal pressure or getting yourself burned in the process. So when it starts to malfunction, you can expect to have a serious cooling system problem in your hands. The following are some common Jeep CJ7 radiator overflow tank problems and how to troubleshoot them.

The coolant in the overflow tank is bubbling

If you notice that the coolant inside the radiator overflow tank is boiling, it is an indication that one of the radiator's cooling fans or the devices connected to it are malfunctioning and that the radiator is beginning to overheat. First, check if the fuses and relays of the cooling fans are in good condition. If they are, run the engine for around 15 minutes or until it reaches the normal operating temperature and check if the fans have turned on. If the fans are running, the problem may be with a bad thermostat, a clogged radiator, or a bad water pump. However, if the cooling fan stays still, the fan or its temperature sending sensor may be malfunctioning and needs replacing.

The coolant from the overflow tank is not returning to the radiator

There have also been cases of the overflow tank getting filled up with hot coolant and stays there even when the engine cools down. If this happens in your CJ7, check the radiator cap and the hoses for punctures and other types of damage. Damaged caps and hoses can allow air to get sucked in to the radiator and prevent the coolant from the tank from flowing back.

The overflow tank is constantly dry or low coolant levels

If you find that the radiator overflow tank of your CJ7 is often dry and you're filling it up more often than usual, there might be a puncture in the tank, coolant hoses and the radiator and the coolant is leaking out of it. Check the tank for any signs of damage; if the tank appears to be in good condition, inspect the hoses and radiator for leaks. We also recommend getting the radiator flushed as well, as there may be a clog in the radiator or in one of the hoses that prevent the coolant from the radiator to circulate back into the tank.

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  • Care and Maintenance Tips for Jeep CJ7 Radiator Overflow Tank 27 February 2013

    Many Jeep CJ7 owners tend to remember the radiator overflow tank only when it's time to refill the radiator with coolant, but it also requires proper use and maintenance from time to time. Also known as the overflow reservoir, the Jeep CJ7 radiator overflow tank is constantly exposed to high-temperatures, vibrations, and other stress-inducing factors while on the road. And while the tank is designed by Jeep to last the life of the CJ7, constant exposure to these stresses might cause it to malfunction. With proper maintenance, the tank is guaranteed to provide years of use with minimal risk of failure. In this guide, we'll show you some simple ways on how to maintain the Jeep CJ7 radiator overflow tank.


    Flush the radiator before refilling it with coolant.

    Ideally, you should flush your CJ7's radiator before you refill it with a new batch of coolant. Flushing effectively rids the cooling system of any rust particles, mineral deposits, and other particulates that may clog the radiator and prevent coolant from circulating to flow to and from the overflow tank. Also, by flushing the radiator before every coolant change, you prevent the new batch of coolant from being contaminated by existing deposits inside the radiator.


    Regularly check for leaks.

    Leaks are a common problem with the cooling system and can lead to an overheating engine to overheat due to lack of coolant or cause air pressure to build up inside the CJ7's cooling system and prevent coolant from circulating properly. We strongly recommend checking for leaks if you notice spots of coolant underneath the engine compartment or on you're the garage floor, or if you notice that you are refilling the overflow tank more often than normal.


    Refrain from using regular tap water as coolant.

    A lot of people tend to use regular water from their tap instead of coolant when refilling the overflow tank in order to save money, but this can actually be more expensive in terms of repair costs in the long run. This is because tap water contains calcium and other minerals that may build up inside the tank, radiator hoses, and the radiator and cause these parts to become clogged over time.