That is a good tip about borrowing a pressure tester. I'd just like to add some advice on proper use. First and most important don't pump up the tester to more than about 15 lbs. If you pump it to the max you run the risk of creating a leak by blowing a hole in the heater core or something. Secondly,leaks usually don't occur when the engine is hot. The way it works is you shut off a hot engine when you park. As the engine cools the hoses,etc relax, and the residual pressure caused by the radiator cap causes about a cup of coolant to be forced out where ever the leak is. Once all the pressure is gone,the system tries to go into a slight vacuum, the leak stops. Each time the car is driven and allowed to cool the cycle repeats until you are way low on water.
Your hose problem was due to a faulty rad cap. The radiator cap has several functions. It covers the hole so junk can't enter the cooling system.
it keeps the system under pressure in the range of 100 to 140 Kilapascals to increase the boiling point or our cars would overheat on a moderate day. As the system cools it refills the overflow reservoir under pressure and then tries to go into a vacuum. The radiator cap prevents this so you don't experience the problem you did.
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