@geomur, I'm confused, but that's just me! Let me summarize to see if I follow it. You have a temperature sender (switch), part number 96-23434. You think it may be broken because the gauge is pegged at 250-degrees. It probably is broken, but there may be other reasons why the gauge is pegged. If you shop around you may find one that's in your budget where you might just replace it and find out, but the ones that I found tonight were definitely outside my casual "just replace it" budget!
The way these devices work is that they put up a resistance to electrical current. The resistance varies as the temperature changes. The lower the resistance the more current that flows and the higher the resistance the less current that flows. It probably isn't surprising then, that a temperature gauge is one whose needle moves proportional to current flow. An ohm is a unit of resistance, i.e., a unit of measure. We use a Digital MultiMeter (DMM) in "ohms" mode to measure resistance.
We are reluctant to say "short" unless we mean zero ohms of resistance. Two bare wires touched together are said to be shorted. Open is the opposite end of the range. It means there is infinite resistance, i.e., doesn't conduct electricity at all. I don't mean to lecture or be picky about terminology (please forgive me), but it is necessary to understand the basics in order to follow the troubleshooting procedure in the technical manual.
I copied the paragraph in the TM (Technical Manual) below. It may help you diagnose if the switch is good or bad.
ARMY TM 9-6115-672-14
AIR FORCE TO 35C2-3-444-32
MARINE CORPS TM 09244A/09245A-14 4-198
4.13.2 Coolant Temperature Sender MT6.
a. Testing.
(1) Shut down generator set, paragraph 2.11.2.
(2) Open BATTERY ACCESS door (Figure 1-2), and disconnect negative battery cable. (Protects both you and your DVVM)
(3) Open left side engine compartment access doors (Figure 1-3).
(4) Remove dead crank switch plate, refer to paragraph 4.14.4.
(5) Disconnect electrical plug connector from coolant temperature sender (2, Figure 4-30) by unscrewing retaining ring.
(6) Set multimeter for ohms, and connect positive lead to temperature sender terminal and negative lead to pin 4. Multimeter should indicate as follows:
At 70°F, ohm range is 108-111 ohms. For each +10°F, add two ohms to either end of range. For each -10°F, subtract two ohms. Example: At 80°F range, should equal 110-113 ohms. At 60°F, range should equal 106-109 ohms.
(7) Connect negative battery cable to battery.
(8 ) Start up generator set, paragraph 2.11.1.
(9) Allow engine to operate while observing multimeter. Ohms indication should decrease as temperature rises.
(10) Shut down generator set, paragraph 2.11.2.
(11) Disconnect negative battery cable.
(12) If indications are not as above, replace coolant temperature sender (2). Refer to paragraph 4.13.2. b d.
(13) If coolant temperature sender (2) meets above requirements, connect electrical plug connector to sender by tightening retaining ring.
(14) Close engine compartment access doors.
(15) Connect negative battery cable to battery, and close BATTERY ACCESS door.
Let us know what you find out?
Evvy-
