Engine fires in busses built on Ford E-Series truck chassis

An insurance company was investigating the loss of a small passenger bus and hotel property where the bus was parked. The driver reported the smell of burning leaves coming from the heating vents, followed by fire in the engine compartment, which eventually consumed the vehicle. Leshner & Associates obtained NHTSA files indicating a defect investigation based on similar complaints.

Ford E-series (Econoline) trucks built from 1975 to 1990 have cowl vent openings large enough to admit leaves and debris. The blower ballast resistor is located in the heater plenum, and can glow red hot when the blower is set on the "low" setting. The resistor can ignite accumulated leaves and debris, resulting in an engine fire. Ford published Service Bulletin No. 84-12-22 in 1984, advising dealers to install a screen mesh under the cowl vent, to prevent entry of leaves. Ford did not correct the cowl vent opening design until the 1991 model.

Later model vehicles of many makes and models continue to make use of resistors located inside the HVAC plenum, capable of becoming sources of ignition if debris accumulates in the plenum.