So I Have a Problem...

Hello fellow truck owners, I have an issue with my 3.9L Magnum. In the summertime, my radiator developed a very small leak under pressure. I usually had to top it off once every few weeks. I suppose that topping it off with plain water from the hose so much eventually replaced all of the coolant in the radiator with water, as the recent deep freezes have left me broken down. The other morning, my mother went out to crank the truck; it was about 9 degrees the night before. She said that the truck hesitated to start, but nonetheless started. After idling for about 15 minutes, I drove it about 3 miles to fill it with gas, and on my way back home I noticed that the heater was ice cold and the truck actually was beginning to overheat. I was showing about 230 on the temp gauge. I popped the hood and did some basic troubleshooting in the gas station parking lot, and I discovered a few things.

1. Radiator was frozen solid. I expected this first, and it was true. You could feel the slush in the hoses.
2. Heater hose going into the cab was ice cold

I limped the truck back home after it cooled down and parked it. A few days later, temps are back into the 60s here, so I went out to look again. I inspected the block first to check for any freeze plugs that may have expanded and popped out. All looked good. I flushed the radiator and filled it back up with straight water, just temporarily to isolate the problem. Started the truck back up, and let it warm up. Truck started to overheat again, and the heat still blew ice cold. The upper radiator hose was hot as hell, but the lower hose and the heater line were ice cold. I've never had a problem with the heat on this truck so I don't believe that the heater core is bad. I suspect a busted water pump, but I'd like another opinion before I tear the truck apart. If I start a water pump repair, its also gonna be a thermostat replacement, which also gives me an opportunity to fix the plenum, which also means tune-up, long story short it's gonna be some $$$.

Most thermostats normally fail open so I would suggest checking it.

Pull it out and look at the center disc to see if it is separated from the upper sealing ring. If so, it's failed.

If it is sealed against the upper ring, introduce it to some boiling water to see if the center disc separates from the upper sealing ring.

If you're going to be pulling the thermostat out to test it, put the hoses back on without the thermostat and start it up with straight water and see what it does then. It's possible that if the waterpump isn't gone, that the thermostat was damaged and is now stuck cold. There is a tiny hole in the thermostat to allow some coolant flow past is even when shut. If the thermostat is failed closed, the hot upper rad hose might be due to that. Which heater line were you feeling? Try popping the heater lines and starting the truck, should start spraying everywhere, if not, likely the water pump.

dudeman2009 said:

If you're going to be pulling the thermostat out to test it, put the hoses back on without the thermostat and start it up with straight water and see what it does then. It's possible that if the waterpump isn't gone, that the thermostat was damaged and is now stuck cold. There is a tiny hole in the thermostat to allow some coolant flow past is even when shut. If the thermostat is failed closed, the hot upper rad hose might be due to that. Which heater line were you feeling? Try popping the heater lines and starting the truck, should start spraying everywhere, if not, likely the water pump.

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Thanks for that troubleshooting info. Will try it out this weekend when I have some free time. As of right now, just leaving it be, school is too demanding to try and fix the truck when I have a perfectly fine Charger R/T to drive.

So a little update. Rain has moved in and ruined my plans to do some troubleshooting this weekend. I was really looking forward to solving this issue and moving on, but I guess nature has other plans. Hopefully, next weekend's weather will cooperate more with me.

Your heater core is most likely frozen along with lower hose. When it thaws out, look for leaks. You can buy a set of flush T fittings and reverse flush the heater core. Just like in a home, when pipes freeze they expand and rupture. I suggest to solve the leak or put enough antifreeze mix in to protect you to -10*