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Author Topic:   Engine Temperature Switch
jimh posted 07-13-2008 01:17 PM ET (US)   Profile for jimh   Send Email to jimh  
Many outboard motor alarm systems include an engine temperature alarm. These alarms generally consist of a thermal-sensitive switch which actuates at a particular temperature. The temperature sensor is generally installed on the upper cylinder head. In engines with two cylinder banks there is typically a temperature sensor for each cylinder bank.

There are often two types of sensors, one for an overheat condition, and another for an engine warm condition. The typical temperature sensitivities are:

OVERHEAT SWITCH
Switch closes at 203° ± 6° F
Switch opens at 170° ± 15° F

ENGINE WARM SWITCH
Switch closes at 96 ° ± 3° F
Switch opens at 89 ° ± 3° F

Source: OMC Service Manual for 90° LOOP V Models c.1992, 120 THRU 140, 185 THRU 225, 250, 300

jimh posted 07-13-2008 01:22 PM ET (US)     Profile for jimh  Send Email to jimh     
To test a switch, the suggested procedure is to immerse the heat sensitive portion of the switch in warm crankcase oil, then heat the oil with an external heat source. Do not use an open flame to heat the oil. Use oil with a flash point greater than 300°F. Monitor the temperature of the oil with an accurate thermometer and check the switch with a continuity checker.

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