i have a1978 f150 4x4 my heater core is leaking. i called to get a new one they asked if it was a high output heater. how do identify this

 

There probably is variations of the size of the core based on this option and probably the only way to make sure is to pull the core and match it at the parts counter. Unless you have the original paperwork for the truck that will specify whether you have this option or you are able to measure the core dimensions pulling and matching is about the only way.

John

 

I agree with John. Pull the old core, then match it up at the parts store. In fact, that is the best way when replacing any heater core. First, call the place and make sure they have one in stock. This way, you can compare exact size and inlet and outlet tubes, bends, length ect. Saves the surprise of opening up the new core box at home, then noticing something here is a little different, something there does not look like the original core.
Remember, install a flushing "T" about 8" out of the inlet tube, then a quick connect 8" from the outlet hose. This will allow you to easily flush the heater core out. Do this, and you'll have hot heat and a heater core that will last longer than the vehicle.
The reason most cores leak is sediment and rust that are trapped inside the bottom of the core. Over time, it causes the seam to crack or rust through, in which the core starts to drip and leak. Flushing the core every other year at least, keeps the core clean, and gunk free. They don't rust = no leaks.
Good luck. Ed