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.