Hello, and thank you for your time. I went outside this morning, and fired up my new 1986 F-250 302 efi. The truck fired right up and was running just fine. I let it sit for maybe 3 minutes and then headed out. I started to drive, and it just started smoking out of the defrost vents. It started light and then just poured. I put the window down, and just barely made it back the few hundred yards and jumped out. It smelled like burnig plastic. I poped the hood, and part of the plastic housing leading to the heater core had melted. WHATS WRONG? Do you think my heater core is leaking and melting the plastic? I really can't find anything about this when I search the forums, and have no clue what would cause this. Thank you and have a great day.

 

The heater and fresh air intakes for the heater filled up with leaves and caught on fire is my guess.


The course of action most likely is going to be to remove the heater box, throw it away, and go get another one from a wrecker.

Make sure the vents and passages are completely free of leaves and foriegn matter.


The cowl is where the heater gets it's fresh air from. It's located at the bottom of the windshield, has the two wiper arms and pivots sticking out of it and is covered in slotted holes.

What happens over time is leaves goes through the slots in the cowl and collects at the bottom of the vents in the cab. There are two vents on each side of the cab in the passenger compartment on non/ac modles, or inspection plates on a/c models behind the kick panels to access the vent passages.

Normally these passages will only fill up to the bottom of the vent and really cause poor heater performance, a wet and mould smell or other such problem.

What happened to you was the worse case scenerio where the heater box filled up with leaves and caught fire.

You can help prevent foregin matter from entering the heater so it doesnt happen again, by replacing the cowl from a 1987-1996. The 1987-1996 cowl has little holes instead of slots and is a lot harder for material to get into the heater.

It's also a good idea to inspect the heater box by removing the blower motor resistor and check for foreign matter around the resistor. The most likely place the fire started on your truck.

Hope this helps....

 

I was going to say the same thing. I've seen leaves and such smoke a couple times from the heater core. I haven't seen it melt the plastic before however. so make sure everything is checked in the vicinity that could have heated up. I still think it's the leaf thing though.

 

There is one other option on your cowl.
After you get everything cleaned out and you have your cowl off you can epoxy some screen underneath which will help keep trash out. You can get the 2 part epoxy at any chain parts store.

 

The blower motor resistors are what start the fire. They get red hot. That's why they are mounted in the airflow.

 

Thanks guys, I'm going to pull it apart tomorrow, and let everybody know what it was. The truck is no longer running, so I have my work cut-out for myself this weekend. Have a great one, and thank eveybody for their help.

 

heater core may be leaking keep a eye on your water

 

Probaby should replace the heater core when you replace the heater box.

The fire could have damaged it.