Preparation is the key to troublefree bus operation in any weather-whether it is sub-zero in International Falls, Minn., or the temperature reaches 110F in Phoenix.
In sub-freezing weather, starting and operating a diesel engine and heating a bus interior becomes a challenge. In extreme cold conditions, coolant temperature in an idling engine may drop below the thermostat setting, which means the engine runs cold with these possible effects:
-If the combustion chamber temperature drops and the fuel is not properly or completely burned, white smoke may be emitted and liquid residue may be left behind to accumulate in the chamber and exhaust passages.
-The residue from incomplete combustion can form varnish deposits on the valves. Under certain conditions, this may lead to valve train damage.
-Injection nozzles can become coated by carbon deposits so that the fuel spray pattern could be restricted or distorted.
-The fuel residue along with condensed moisture can wash down the cylinder walls, removing needed lubrication, which may cause accelerated wear of the piston rings.
-The lubricating oil temperature drops and moisture can condense in the oil, possibly contaminating it and accelerating wear of the bearings.
A diesel engine that has idled for extended periods-more than 30 minutes in cold weather-could have a shortened life span. However, it is recognized that there are legitimate situations where extended engine idle is required-for example, keeping the school bus body warm while waiting for the football team.
Start your engines
Many improvements have been made in diesel design that have resulted in engines that start readily and perform well in extreme cold. In addition, electronic fuel systems have improved diesel running and starting capabilities. Engine engineers recommend that a diesel engine not idle for long periods of time; the driver should depend on the equipment's ability to start in cold temperatures. Some cold-weather engine starting aids include:
-Glow plugs. These heating elements come standard on some diesel engines. The plugs are installed in each cylinder and provide a hot surface to ignite the injected fuel to ensure cold engine starting.
-Intake manifold heater. This is an automatically controlled electric heating element or fuel-fired device to heat the intake air during engine startup.
-Fuel quality. Find a fuel supplier that can provide winterized fuel with a cetane rating of 45 or more. A cetane rating of 50 is best. High-cetane fuel will support faster starts and reduce white smoke during warm-up.
-Ether kit. Ether is injected into the intake manifold to ensure starting in extreme cold. Ether is not an option for engines with glow plugs or intake manifold heaters and should be used only where 110-volt power for other starting aids is not available. Only measured shot chassis-mounted systems should be used; do not try to boost engine starting with ether aerosol spray cans-severe engine damage could result.
-Cylinder block/coolant heater. This option improves startability and reduces warm-up time by heating the coolant surrounding the combustion chamber. A block heater can be turned on as soon as the engine is shut down.
-Oil pan heater. An oil pan heater will aid cold starting of diesel engines by warming the temperature of the engine oil to improve its flow. This provides faster cranking speeds for quicker starts and improves lubrication of moving engine parts.
-Battery heater. Battery power is affected adver sely by low temperatures. A warm battery will deliver more power to the starter for faster cranking speeds. This can be accomplished through a trickle charger supplying the battery during vehicle downtime, which will keep the plates and electrolyte warm for maximum performance. A warming pad can be used to keep the entire battery case warm.
Keeping it warm
Once the bus engine has been started in cold weather, it is important to keep it warm. One option is to shut off heater fans in the bus body. In addition, shut off all auxiliary heater fans in the bus interior to promote faster warm-up of coolant in the engine. Interior heater fans will only rob heat from the engine and slow engine warm-up. Turn the heater fans on when it is time to drive the bus to start the student pickup route.
Consider an engine warm-up device. Some diesel engines can be equipped with an electronically controlled exhaust system restriction valve that increases operating load on the engine. This device speeds engine warm-up and decreases white smoke.
Though useful in maintaining minimum engine coolant temperatures when the temperature drops below freezing, use of a winter front requires caution. If the coolant is able to maintain a temperature of 160?F (71?C) or higher, a winter front is not required regardless of ambient temperature. If left unopened while the engine is under load, a winter front can cause a restriction in air flow that can result in higher exhaust temperatures, power loss, excessive cooling fan usage, reduced fuel economy or engine overheating. The bus driver continuously must monitor the dash gauge to ensure engine temperatures do not reach excessive levels.
Preparations for warm weather typically are not as extensive as those required for cold weather, but they are no less critical. It is important to ensure vehicle fluids are at proper levels and that hoses and belts are in good working order.
In addition, air flow is a critical consideration for any vehicle, especially a bus. In many bus models, the vehicle's intercooler-a heat exchanger that cools air coming from the engine turbo charger-is located in front of the radiator. There is a space between the intercooler and the radiator where dirt and debris can accumulate on the face of the radiator and block the free flow of air. Use an air gun or water from a hose to clean out the space. This may require removal of the intercooler to gain access to the air side of the radiator.
Fluids and more
It is important to ensure coolant is maintained at proper levels. Beyond that, it is just as important to make sure the coolant has the proper concentration of antifreeze or other protective additives. Make sure the water/antifreeze mix is right-usually 50 percent water, 50 percent antifreeze-and make sure conditioner additives, which protect the engine and radiator from corrosion, are tested for the proper concentration. Also, check the pressure cap to be sure it can maintain the manufacturer's specified pressure in the cooling system.
Finally, check the engine thermostat, along with belts and hoses. Look for loose or frayed belts, or rubber hoses that are hard, cracked, mushy or swelling.