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EFV-8 Club Forum / General Ford Discussion / Temp Sensor Testing

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Discussion Topic: Temp Sensor Testing

51woodie

09-24-2018 @ 8:08 AM

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My temp gauge was not working (pegged to hot) on my '46 coupe. Troubleshooting with a multimeter found that the short wire from the main harness to the LH sensor was open, although it looked good. Replaced the wire, started the engine and the gauge reads cold. Good stuff! Now the gauge reads cold for a bit, then when the engine stars to warm up it pegs to hot. The mechanical gauge is just starting to register temp. I've searched the posts and have not found any info on sensor testing that is of help to me. What I have read in the Ford manual describes how the sensors/gauge works, so the questions are:

How can I test the left sensor? Ohmmeter on both connections will show continuity when cold?
Left sensor will open if tested in boiling water?

What is the Ohm reading on the right sensor, connector to sensor body when cold?
Does the Ohm reading change as the sensor warms?

09-24-2018 @ 10:34 AM

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Many posts about about your problem on this forum and the Ford Barn Forum. Use the search tool and type in 'temperature sensors' or 'temp sensors'. Here are some of the posts I found >

https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=18&Topic=1912&keywords=temp%20sensor

https://www.fordbarn.com/forum/showthread.php?t=204434&highlight=temp+sensors

https://www.fordbarn.com/forum/showthread.php?t=102106&highlight=temp+sensors

https://www.fordbarn.com/forum/showthread.php?t=225522&highlight=temp+sensors

This message was edited by MG on 9-24-18 @ 10:50 AM

51woodie

09-24-2018 @ 3:21 PM

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Thank you MG. The last link you posted in your reply was most helpful. For some reason, I didn't find that one in my search. I'll have to go through the checks to see what shakes out.

Drbrown

09-24-2018 @ 8:52 PM

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In summary, your research will probably show my experience.

On my '47 the driver's side (left) OE sensor malfunctioned, as they sometimes do, and my gauge would register/spike to "hot" well before my aftermarket gauge sensor in the same head was just showing the engine warming up. After the engine got up to running temp, the dash gauge would finally drop down to a normal level. I did what many do and wired a by-pass of the left OE sensor, connecting the passenger side (right) directly through to the gauge. That stopped the dash gauge reading from spiking to hot and provides a more accurate reading..

TomO

09-24-2018 @ 8:55 PM

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The sending unit with 2 terminals is just a switch that opens when the engine is overheating. Try bypassing it by connecting both wires to one terminal. The sending unit with one terminal is the one that causes the needle on the gauge to reflect coolant temperature.

Tom

1934 Ford

09-26-2018 @ 7:22 AM

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Optima responded.
Production difficulties caused the problem and the 6 Volt Optima will be available again within a month.
http://forums.aaca.org/topic/315809-optima-6v-discontinued.

I'll wait.

1934 Ford's since 1972

51woodie

09-26-2018 @ 4:33 PM

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Thanks to MG, my problem with spiking temp is solved. The left sensor is the culprit, I started the engine and let it idle to warm up.. The temp gauge progressed nicely to about half way then spiked to hot. I jumped the left switch and the gauge went back to the middle. Bad left switch. I have to buy a replacement, so any suggestions on a reliable source?

Drbrown

09-26-2018 @ 7:50 PM

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Since I don't have a concourse grade car, I opted for what I thought was the best arrangement for me. I kept the right-passenger side sensor and wired it direct to dash gauge. I removed the left-driver's side two-terminal sensor and installed the sensor of my aftermarket mechanical temp gauge. This way I see whats going-on each side and they show about identical temp levels. One advantage of this set-up is that if one of the thermostats misbehaves it should show on the related temp gauge, especially during warm-up.
Sometimes when I use my heater, connected to right side, that side shows a bit lower reading.

If you what to keep your stock set-up I've most often seen two-terminal sensors on Ebay but if you're patient you'd probably also find them on the Ford V8 or Ford Barn classifieds. However, given the problem with this unit is common, you may eventually face the same problem again.

This message was edited by Drbrown on 9-26-18 @ 7:58 PM

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