Wednesday, November 09, 2005

Installing Fan Over-ride Switch On A Thomas School Bus With 3116 Cat Engine

Our buses [between 1995 & 1998] with 3116 Caterpillar diesel engines overheat in hotter ambient temperatures 30 degrees Celsius and up [90 degrees Fahrenheit]. They come with the same components as the Cummins equipped school buses but they reach very close to shutdown levels @ 220 degrees. After trying everything to cure the problem we decided to install a engine cooling fan over-ride switch on the dash. The operator just flips it on before climbing a steep grade just to get a jump start on the engine cooling process.

The engine fan motor is hydraulically actuated and electrically controlled by a coolant temperature switch [shown above]. When engine temperature reaches 200 degrees the coolant switch opens creating an open circuit. The engine fan is now rotating at engine RPM maximizing it's cooling potential.

The dash switch is wired in between the sensor wire and the sensor in series, and that's all there is to it. When the switch is flipped to the open mode you are creating an open circuit which turns the engine fan ON full blast.
The operator who usually drives the same school bus everyday knows his or her bus and it's habits. So he or she knows when to flip the fan switch. It may be a band aid solution but it works! After fighting the problem for a long time futility sets in and sometimes it's not a bad idea to IMPROVISE!


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