My '89 F250 5.8L is leaking coolant pretty good from what looks to be a drain on the passenger side firewall on the engine compartment side. My only guess is this is coming from the heater core. Would that be a fair assessment?? Would it be strange for the heater core to go bad now when I'm not running the heat? That's probably a dumb question but figured I'd ask anyway. I watched a couple videos on YouTube but didn't see the drain like mine has. They were working on 89's like mine. Below is a picture of the drain. Is this just some sort of overflow drain so in case the heater core does leak it won't leak into the cab?

 

My guess is it is a condensate drain for the AC. If your heater core developed a leak you would see the signs come out of there. I have a 90 and my core went as I was driving it home for Christmas and I could small it and if fogged up my windows bad.

 

The heater core in these trucks is always a bypass loop of the thermostat.
In other words, it does not matter if the heat is on or not, coolant & pressure are always there.

The easiest temporary fix is to join the two ends with a 1/2" copper slip coupling, or loop one of the heater hoses back to where the other leaves the engine.
You'll lose a lot less coolant with the first method.

 

Just replace the heater core. It's really easy in these trucks.

 

Yeah it doesn't look all that bad to change it out. If I do I'll probably just get the Motorcraft one as opposed to the $30 Chinese version. A lot of reviews say they leak within 6 mos to 2 years. I drove the truck 2 more times and there is no more coolant leaking out of there. I estimate I only lost a few ounces. It seemed to stop as quick as it started. I would think it would have leaked again.