Temperature gauge problem

[jerry44]

I have a 2002 196 the temperature gauge is pegged hot but the boat is not running hot. For a while it would jump abruptly from normal to pegged hot but shows hot all the time now.

[bhectus]

sounds like your sending unit is bad.

[DanielC]

What engine does your boat have?

The temp sender is a thermistor, a resistor that changes value depending on how warm it is.
If it is hot, the sender has low resistance, and cold, higher resistance.

Disconnect the wire from the temp sender. This should cause the temp gauge to go to cold. Short the wire to ground, and the temp gauge should go hot.

There is more than one temp sender. Only one goes to the temp gauge.

[jerry44]

What engine does your boat have?

The temp sender is a thermistor, a resistor that changes value depending on how warm it is.
If it is hot, the sender has low resistance, and cold, higher resistance.

Disconnect the wire from the temp sender. This should cause the temp gauge to go to cold. Short the wire to ground, and the temp gauge should go hot.

There is more than one temp sender. Only one goes to the temp gauge.

Thanks Daniel,

The engine is a PCM GT-40. Can you tell me where the temp sender is located?

[jankedm]

It should be located on top of the circulation pump, (not to be confused with the RWP). If you look down from the top on the front of the engine, the end with the two belts, you can see it. It is located behind the largest pulley that both belts run on. It is brass with one wire comming off of the top. On mine, it was slightly angled towards the RWP and set back in a little. I hope my description made sense. David

[jerry44]

Thanks David.

I noticed that the other day and was wondering if that was it.

I was thinking today that if the resistance goes up as it gets hotter then an open circuit would peg the gauge. That being the case it may be that the wire is loose at the gauge.

[jerry44]

What engine does your boat have?

The temp sender is a thermistor, a resistor that changes value depending on how warm it is.
If it is hot, the sender has low resistance, and cold, higher resistance.

Disconnect the wire from the temp sender. This should cause the temp gauge to go to cold. Short the wire to ground, and the temp gauge should go hot.

There is more than one temp sender. Only one goes to the temp gauge.

I disconnected the wire from the temp sender and the gauge is still pegged hot. I touched the wire to ground and I think I saw the needle on the gauge move slightly one time. This was all with the switch on. My boat is a LE so I pushed the start button one time to turn the switch on.

Also the check engine light is on. I think that's normal when the switch is on but I could be wrong on that.

I would guess that my next step is to disconnect the wire from the gauge and if it goes to cold then that would mean there is s short somewhere?

[jerry44]

Temperature gauge

I removed the gauge and after I unplugged it, it was still on 240.

I can shake the gauge and the needle will move between 160 and 230.

[DanielC]

I think the gauge temp sender is on the intake manifold, behind the distributer, slightly to the right side of of the engine. If you disconnect the wrong wire nothing will change with the temp gauge.

[jerry44]

The one I unplugged was on the water pump. Do you know what that one is for?

With the gauge unplugged shouldn't it show cold?

Thanks

[jerry44]

I see one on the right side of the distributor (looking toward the front of the boat). It has 2 wires. One of the wires is in the harness with the wire that goes to the water pump. The other wire come from somewhere else and has a braided shield on it.

[AirTool]

I don't know about 2002 ford engines....but usually there are two temp sendors: One for the gauge and one for the computer.

[DanielC]

The gauge temp sender has only one wire, both GM and Ford engines. As far as I know.

[jerry44]

The one with only one wire is on the water pump and that's the one I disconnected.

So I guess it's the gauge.

[DanielC]

Here are the two temperature senders I found on my 1997 GT-40 engine. The one with my finger pointing to is for the computer. It has a single green wire on it. Mine is located on some extra plumbing that was added to install a heater. This sender is normally on the intake manifold, buried just behind, and to the right of the distributer.
The other picture, of the circulating water pump has a brown, or tan wire on it. Shorting the connection on it makes the temp gauge immediately peg full hot. If I connect a small test light to it, and ground the other end of the test light, the light glows dimly, and the gauge reads about half scale.

Find the temp sender with a single brown, or tan wire on it. I am not referring to two wires, I am using "tan" or "brown" because what I call brown , you may call tan. or the other way around.

If your gauge is pegged, disconnect the brown (or tan) wire from the sender. Turn the key on, and see what happens. If the gauge stays at minimum, suspect the sender. If the gauge stays full hot, go under the dashboard, and remove the brown (or tan) wire from the temp gauge. if the gauge reads low, the wire is shorted. if the gauge still stays high, I would suspect the gauge.