Jimmy,
You need a multimeter and set it to read Ohms.
Read the Ohms (resistance) when sender is cold and when the temp is at operating temp.

Place one lead on the wire connector and the other lead to the section of the sender that contacts the manifold.

It sounds like you may have the wrong sender for that gauge.
Call your vendor and verify you have the correct resistance readings for the temp gauge.

Good luck,

Ed
FFR1997K

 

Thanks Ed,I will try that. Is there any way to ohm out the SW gauge to see what range the SW gauge is?

 

No,
The SW gauge works off a voltage reading.
The Temp sender is compared to a known reference.

Ed
FFR1997K

 

Ed, with the car off I am getting 15 ohms on the sender. As soon as I turn the car on, I get 1 like an open circuit the entire time the car is on. After the car heats up and the thermostat opens I turn the car off and I get 25 ohms and the gage is on 190 degrees.

The problem seems to be when the car is on the sender acts like the circuit is open (?). I do have silicon on the threads to keep from leaking. Is the sender grounded through the threads?

 

I disconnected the wire from the sender to the gauge and the sender worked fine, as the car heated up the ohms changed. The sender wire has continuity so I think the problem is in the gauge. Sound reasonable? Can I check the gauge out to see if there is a short in it or something?

 

Jimmy,
From what you have told me in the above post, the temp gauge is operating fine.
The problem being the incorrect temperature reading.

This would lead me to believe the gauge is either incorrectly calibrated, or the temp sender is the incorrect resistance value range for that gauge.

Contact the vendor you purchased the gauge / sender from and verify the part numbers are a correct match.

There is nothing you can do other than verifying the correct combination of parts.
Maybe someone on the other forum can give us a part number for the SW temp gauge sender.

I'll see what that turns up and you contact the vendor.

Ed
FFR1997K

 

Jimmy,
One more thing I want you to verify.
You should have three wires on the SW gauge.
One is +12 volts from ignition, Ground and a wire that goes to the sender.

How the gauge works:

The gauge is trying to find the resistance value of the sender to determine engine water temp.

The gauge only knows what the reference voltage is since you apply the reference voltage to the gauge.
To determine the resistance of the sender the gauge looks at the amount of current flowing in the sender wire.
Ohms law states that Resistance = voltage / current.
So, if we know what the reference voltage is and the ammount of current flowing in the sender wire, we can use Ohms law to ddetermine the resistance value of the sender.
Remember, as the temp increases, the resistance changes.
As the resistance changes, the current is different in the sender wire.

I know this explaination is rough, but maybe it will help you understand how the gauge works and how it is connected.

So, if your gauge immediately goes to 280 deg as the ignition is on, you may have the wires connected incorrectly, or the resistance value is out of the gauges tolerances.

Let me know what you find out.

Ed
FFR1997K

 

The SW water temp sending unit part number is 280ED-F. The oil temp sender is 280EE-F. What does the gauge do if you remove the wire at the sender and turn the ignition to on. With the disconnected wire not touching anything, it should (if it functions like the Ford system) stay below the bottom of the scale (cold). If the sender wire is touched to ground, the gauge should peg to the top of the scale (hot).

 

Ed and Paul, thanks for your help. Long story short, I contacted the vendor that I bought the sensor from and I was sent the wrong one. The one I got was the 280EA, not the 280ED-F. Glad it was something simple!

 

Glad to hear you got it fixed.
Happy to be of service.

Ed
FFR1997K