Freightliner School Bus Heating System
The conventional school buses heat up faster than a pusher bus because of the slightly smaller area the floor heaters have to cover. It still takes a while and we keep up with maintenance such as changing thermostats every 2 years along with the coolant as recommended by Mercedes. We use bulk coolant that’s delivered to a tank outside and plumbed into the shop to hose reels and a dispenser.
There is a lot of heat loss in the passenger area because of the immense amount of space and the 60 to 70 feet of one inch heater hose going both ways to circulate coolant to the heater cores. We have experimented running the pressure line from the engine directly to the cab heaters and then back with some success. There is just too much space to heat up and when the floor heaters are on high fan speed the temperature drops down quickly during frigid temperatures.
Different Engine Fans Make A Difference
The viscous engine fan contributes to a slow build up of heat because of the constant drag on the clutch built in to the fan hub. Even when the engine is cold the fan never free wheels to assist engine warm up. The electric and air clutch fans are much more efficient in this area and don’t kick in until engine temperature is over 180 degrees or even higher depending on the engine specs.
The Coolant Boost Pump
All school buses come with a coolant boost pump to help circulate coolant through the one inch heater hoses to the inside rear floor heaters. Each floor heater has two fans at each heater core mounted underneath two of the bus seats. You would think there would be more heaters at the back of the bus but the 2 underseat units is all that comes from the factory.
In the past we have installed an extra underseat heating system that we robbed from a retired bus to accommodate for lack of heating especially in a 40 foot pusher school bus. Some of the operators climb a grade before leaving for their regular run to warm up the heating system. Some bus runs start off going downhill to their destinations so heat will take some time to happen.
Diesel Fuel Coolant Heaters
A great solution to this problem is the introduction of diesel coolant heaters. The Webasto and Espar heaters do an excellent job to get a bus going in the morning and assist the block heaters that come standard from factory. We order diesel coolant heaters from the factory and have been since 2006. These heaters have to be cycled to keep the internal plumbing clean so we run them every service to test them out even during warm months.