I have 78F250 with the HO heater & no AC. I just had my engine built & since I got it on the road I'm having coolant leak from the heater core area into the passenger floorboard. Never had this issue before prior to engine removal/replacement. Tonight after looking at my shop manuals I believe the mechanic has reversed the heater hoses where they connect at the firewall. Will reversed hoses (in going in the out / out going in the in) cause leaks? Thanks.

 

Nope. It doesn't matter what hose goes to what side of your heater core. All reversing the hoses probably did was break loose some stop-leak or something else plugging a pre-existing hole. You can either replace the heater core or if you are tight on funds and time, loop the heater hose from the intake manifold to the water pump. Keep in mind that looping the hose will cause your heater to not work. All it will do is move air.

 

Thanks RNOVRIT -I'll just connect the hoses together in the interim to bypass the core.

I am curious though - is it possible that with my fresh engine there is pressure or flow changes which could have made this core leak?

 

Heater core only cost me $20 at NAPA. pretty cheap... PITA to change though

 

It was probably the sitting around until the engine was back up and running running and pressure back up that caused things in the cooling system to loosen up.

Did you replace the water pump and rad cap ?