There are three variations of the float type of low oil shutdown. One is a lighted rocker switch that is connected to a float switch in the engine crankcase. When the oil is low the switch will flash as the engine rotates, and the engine will not run. Some engines are equipped with an optional Low Oil Shutdown System that includes a light but does not include a rocker switch. Some engines are equipped with an optional Low Oil Shutdown System that does not have a rocker switch or a light. In each type the float switch will shut the engine off while it is running if the oil level in the crankcase falls below a predetermined level. Oil must be added to the engine to bring the oil to the proper level before the engine will start.
Check the LOS switch while it is in the engine. The engine must be level and the oil level at the full mark. Place the speed control in the run position. Remove the spark plug wire from the spark plug. Install a gap type tester connected to the spark plug wire and a good engine ground. Spin the engine over using the electric or recoil starter. A bright blue spark should be seen at the tester. If not remove the blower housing and disconnect the LOS lead from the ignition module. Reinstall the blower housing and spin the engine over. If spark occurs now replace the LOS switch. If no spark is seen replace the ignition module.
If equipped, the indicator light will flash if the oil level is at or below the add mark and the engine is turned over while attempting to start. Test by turning the engine over with the oil level below the add mark. If the indicator light does not flash replace the indicator light.
Left: Tecumseh low oil float switch 611303.
Right: Tecumseh low oil pressure switch 611193.
Left: Low oil pressure sensor
Test the sensor on a running engine using an ohmmeter or continuity tester with one tester lead connected the sensor terminal (with lead wire removed) and the other to an engine ground. An open circuit should be found with the engine running and continuity should exist when the engine is shut off. If continuity is found or the tractor oil pressure indicator light is on or comes on at low engine RPMs, remove the sensor and check engine oil pressure with a master oil pressure gauge. The oil pressure of a running engine should be above 10 p.s.i. (.700 bar). If below 10 p.s.i. (.700 bar) an internal engine problem may exist.
Right: Current limiter type low oil sensor set in recess in engine base.
This sensor must use a # 194 bulb in series with the sensor for proper operation and to prevent sensor damage. Remove the sensor from the engine and attach the electrical plug. Attach a jumper lead from an engine ground to the threaded portion of the sensor. Place the keyswitch in the run position. The indicator light should come on with the tip of the sensor in air and go off when oil covers the sensor tip. The response time of the sensor is between 5 and 15 seconds with 13 volts D.C. at the battery. Lower battery voltage will result in a longer response time. Use teflon-type pipe sealant on the sensor threads to prevent oil leakage when reinstalling.