[66sprint6]

Our '67 LeMans came with no hoses going to the heater core. The engine had been replaced and the heat and AC had not been reconnected. I don't know if it was laziness or if it was because the heater core was leaking. I don't see any obvious signs of a leak, but who knows how long it's been since water flowed through it. I want to test it in the car. If it's OK I want to hook it up, because my son drives it daily, and it's starting to cool off here.
What can I rig up to check it? Air pressure? Vacuum? I don't have a lot of equipment but don't mind purchasing something inexpensive if it will tell me what I need to know.

[Sirrotica]

Most times you'd pressure test the system with a radiator pressure tester, and look for coolant escaping, and the ability of the pressure gauge to hold a reading.

If you want to test it dry you could put one hose on, and plug one hose on the other side and pull vacuum on, or pressurize it, to see if it will hold a steady pressure rate on a gauge. A vacuum pump used to evacuate A/C systems can be used if you want to test it dry. Pressure testing should be regulated down to 10 lbs, as to not damage the old core.

Or the no frills way would be to just hook it up and see if it leaks, chances are pretty good a betting man would win the bet on a leaker. In 50 years of wrenching as my profession, I've never seen a by passed heater core that was good.

If it's a driver, you might just want a new one anyway because the old one is most likely full of sediment and would work marginally anyway......