I need to test my temp. guage. I think I would start by grounding the wire at the sending unit. I have a Blackmax 150 HP. XR2. Can you tell me how to test the guage and the sending units?
OEM temp senders are only suitable for warning horns. They will ground at overheat (maybe 200*F or so). If you have a temp gauge sender, the resistance will change with rising water temp. The gauges have a definite ohm range. A OEM spec sheet may give that to you.
Tan wire at top of (STB) head if I recall. Disconnetct bullet connector and ground with key on. Temp guage should peg. If it does then the sender is problem. If not, look to the guage.
Chevy, One of the twin temp senders may be for a gauge, or they could both be for idiot lights. You need to figure that out. Is there a third temp sender on the cylinder head? That may be for a gauge. The only way to test it is to get a spec sheet on the gauge and a candy thermometer and put it in a pot of water on the stove. Measure resistance at a given temp and compare to spec sheet.
thanks for the tips. I will check this out this weekend. Maybe my Clymers manual will help me with some info on this. I'm having to get familiar with the boat and it's eguipment. Your help is greatly appreciated.
You measure the sender resistance with an ohm meter. cold = 240 ohms, Hot = 33 ohms. Cold would be anything less than about 80 degrees. Hot is anything above "about" 210 degrees. Simply grounding the sender lead is not a test of the gauge. The wire itself may be the issue. Grounding the "S" terminal at the gauge is where this can also be done. The gauge also requires +12 volts (key on) and ground. Missing either of those means the gauge won't work. The difference between a sender and a sensor is that a sender is a resistance element and is used with a temp gauge. A sensor is nothing more than a heat sensitive switch (on or off). For outboards these are normally open switches. When an overheat occurs the switch closes thus grounding the alarm system and sounding the alarm horn.
