Heater Performance - Cab Heat Expectations
84ford3Article No. 84-23-8
HEATER PERFORMANCE (6.9L) - CAB HEAT EXPECTATIONS
LIGHT TRUCKS 1983-85 F & E-SERIES
Many owners of 6.9L diesel-powered Ford trucks are first-time owners of diesel engines and prior owners of similar trucks with gasoline engines. Their prior ownership has produced certain expectations about how their trucks should perform, particularly in regard to cab heat characterstics. Some owners have expected the cab heat performance in the 6.9L diesel to be the same as their similarly equipped trucks with gasoline engines; however, warmup time for a diesel engine may take up to 3-5 times as long as a comparable gasoline engine. These owners may attribute this condition to a malfunction of the cooling system. However, the condition may be normal because of the inherent nature of diesel engines.
The reasons for the relatively long diesel warmup period are:
^ Very low heat rejection to the coolant for diesel engines at light load. This characterstic is a result of the inherent low fuel consumption of diesels at light load and the fact that light load diesel operation requires very low fuel-air ratios which produce combustion temperatures much lower than those obtained on gasoline engines.
^ Diesel engines tend to be heavier and have larger cooling and oil capacities than gasoline engines. This means more total heat input is required to achieve normal operation temperature.
The 6.9L diesel engine is typical of the above diesel engine characterstics. It has a (31) quart (U.S.) cooling system and a (10) quart (U.S.) engine oil lubricating system.
The Light Truck Owner Guide, under the heading "Cold Weather Operation" cautions the owner that "the diesel engine generates very little excess heat at idle, and prolonged idling will not improve heater performance nor aid in initial cab warm-up".
After driving the truck at a speed of 30 mph or above for a relatively short time (time period varies depending on ambient temperature), the engine will start to generate sufficient cab heat. At speeds above 50 mph heater performance may be better than gasoline engines heaters. Trucks with 6.9L diesel engines contain additional insulation to keep the heat in the cab once it is heated.
'Winter-fronts" are commonly used on trucks in cold ambient temperatures (climates below 0~F, -18~C) to improve cab heating time. Dealers may want to recommend that the customer purchase one as an optional item for cold weather use.
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