1999 Ford F350 5.4L
This week a coolant leak sprung on my truck. Here are the symptoms. When I first noticed the leak I looked under the hood and the reservoir was empty. I filled back up with water and drove for a little bit. After stopping I looked under and a pretty steady drip was coming from the back side of engine(unknown location) due to it being to tight to see anything. The reservoir was empty again, I took the cap off and the air pushed out and the reservoir filled back up with water. I drove around most of the day and kept adding water. The truck has been right in the middle on the temp gauge the entire time with no signs of overheating. I went to oreillys and got a bottle of Bars and put in the coolant system. The next day I tested and didnt notice any leaks and reservoir stayed full. After further investigation I think I may have another issue. I was squeezing(almost pumping the big radiator hose that goes from the top of radiator to the thermostat and noticed a small squirt of water coming out just under where the thermostat is. When i looked closer it looks as if someone fixed that hole /crack previously with some kind of putty or substance. if you look at the video you can see exactly what im talking about. Can anyone help diagnose why when i was taking the cap off the reservoir would fill back up and also by looking at the video can i clean that old putty off and put on on something new? If so what?

 

First, I hope when you were adding 'water' you were actually adding a water/coolant mix, not straight water. (From your video it looks absolutely clear, which means you might be running on just straight water).

Second, when you opened the reservoir tank and air rushed out and the tank filled, that's because the system is intended to be pressurized, so that's normal. It's why the cap says 'do not remove when hot.' If the system had been full, hot liquid could have squirted out and burnt you.

Third, Bars Leak isn't really a great thing to add, as it can cause clogs in the system if you add too much. Definitely don't add more. Better to find the actual leak (which you may have done but you should still check more).

As for that putty, that looks like it's a band-aid from a previous owner, could be JB Weld. Years ago I used it on a radiator fitting to get me by until I could get the radiator actually replaced, not a great solution for long-term use. You would need to peel that off to see where the leak actually is and fix it properly. It could just be the gasket between the thermostat housing and the intake, which means pulling it apart, drying everything, and putting a new gasket in. It could be the thermostat housing (which is not uncommon), and is basically the same process as just replacing a gasket, just with a new housing as well. It could also be damage to the intake manifold, which means a new intake manifold and quite a bit more teardown to fix it properly. Find out if this is your only leak or if you have another at the rear of the motor somewhere, and address it all at once.