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Old 08-05-2017, 09:19 AM   #1
tubman
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Default I now have TWO temperature gauges

After all the screwing around I did, I still couldn't get the temperature gauge on my '51 to work. Since that is the only thing wrong, and I've already been down for two years, I decided to install a mechanical gauge so I wouldn't lose the rest of the summer. I figured a way to install one with out drilling or cutting any holes anywhere and finished the job yesterday afternoon. I removed the stock drivers side sensor so I could install the sensor for the mechanical gauge. Now I have two wires hanging there, so I connected them together and taped the connection. I went in to start the car, and the mechanical gauge works just fine. I take a glance at the cluster to make sure I have oil pressure, etc. and lo and behold, the stock temperature gauge is now working!

I had checked the drivers side sensor for conductivity several times and it always showed zero ohms, meaning it was closed. However, I only checked it while the ignition was off. I can only surmise that there was something electrically bad with the "switch" sensor that only manifested itself when the circuit was operational. I'll figure that out later, but for now, I'm a happy camper who will live with the luxury of not one, but two temperature gauges!
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Old 08-05-2017, 09:37 AM   #2
JSeery
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Default Re: I now have TWO temperature gauges

That's cool that you found the problem!
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Old 08-05-2017, 09:44 AM   #3
drolston
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Default Re: I now have TWO temperature gauges

Glad you got something working. Having failed to find a NOS temp sender, I just ordered my third repo in three years. The current one goes full hot any time the engine temp goes over 190 degrees (measured at head water outlet with IR heat gun). I bypassed the driver side sensor to be sure the real sensor was the problem.

If anyone has a good original unit to sell, please let me know.
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Old 08-05-2017, 10:05 AM   #4
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Default Re: I now have TWO temperature gauges

An interesting observation I'd like to share. I had this engine on my test stand for a while, making sure the carburation and ignition systems were working correctly and also to develop the 6 volt tachometer driver we make. The stand has quality mechanical gauges on it, and I got quite familiar with their readings under a lot of conditions. The stock oil pressure gauge in the car seems to be spot on with the one on the stand. Hot idle is about 25 on the stand and a bit above the one quarter mark (20 lbs) in the car. At 2000 RPM, I have 55 on the stand and part way between one half and three quarters in the car. It's a little different with the temperature gauge. 160 on the mechanical is a little over half scale on the car gauge, while 180 is three quarters scale on the car. It's all relative, because the car gauge just has "C" and "H"; it just seems it runs a little high to me.
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Old 08-05-2017, 10:23 AM   #5
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Default Re: I now have TWO temperature gauges

Something else; I dissected an inoperable temperature sensor to see what made it tick. I found a lot of corrosion on the sending apparatus itself. When I cleaned it up, the unit started working again. I soaked it in Evaporust to get the rust off of the unit, and dressed the points. When tested, it gave of the same type of signals as my good units, only a bit more defined. Also of interest is that there is an adjusting screw on the points, which would allow you to calibrate the unit.

These units are rebuild-able. They are constructed in such a way that the sensing apparatus is completely sealed off from the engine coolant. One could remove the guts from the unit, screw the housing into the head, insert the sensing part temporarily and with subsequent test runs, could adjust the unit using the screw on the points. After you got it where you wanted it, you could use epoxy to put the unit back together permanently using some epoxy. The sending apparatus is held into the housing with 3 small crimps in the housing holding the working part in. These are easily removed with careful use of a Dremel tool. It is a little more difficult getting the guts out, but with the help of a couple of jewelers screwdrivers, I go it apart. There are two steel washer on top of the fiber insert, that has a brass cup in the bottom. Once you get that out, you have access to the actual sending unit, which can be removed with a pair of needle-nose pliers. The points will probably be corroded as well as the spring brass strip the contacts the cup in the bottom of the fiber insert. Clean all of the areas and I bet that the sender starts working again. Then it's a matter of putting it back together again with epoxy to hold the whole thing together. Since the internal contact is spring loaded against the cup, I used a "C" clamp to hold it together against the spring pressure while the epoxy hardens. One last piece of advice : before you remove the guts, make sure you note the orientation of them to the grooves on the housing.

For the price they are getting for repop sensors, taking a shot at rebuilding the old one seems to me to be a viable alternative.
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Old 08-05-2017, 10:27 AM   #6
JSeery
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Default Re: I now have TWO temperature gauges

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Very interesting information Tubman. Do you have some photos?
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Old 08-05-2017, 10:51 AM   #7
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Default Re: I now have TWO temperature gauges

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Originally Posted by JSeery View Post
Very interesting information Tubman. Do you have some photos?
I was in such a hurry to see if this would work that I put everything back together before I could take any photos. I used a minimal amount of epoxy for appearances purposes, so perhaps I'll try to take it apart and see if I can get some.
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Old 08-05-2017, 03:35 PM   #8
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Default Re: I now have TWO temperature gauges

You might consider keeping the second gauge and hooking it to the other head. I have that setup in mine.
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Old 08-05-2017, 07:02 PM   #9
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Default Re: I now have TWO temperature gauges

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Originally Posted by 4dFord/SC View Post
You might consider keeping the second gauge and hooking it to the other head. I have that setup in mine.
This is what I already have. You have to understand that what I am trying to do here is to show people how to understand how these things work and how to fix them. I think I'm on the right board for this. I don't think two aftermarket temp gauges in a "Pep Boys" panel is gonna cut it at an Early Ford V8 Club meet.
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Old 08-06-2017, 10:55 AM   #10
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Default Re: I now have TWO temperature gauges

"Jseery" - Here are the pictures I took yesterday. Please excuse the initial hack job I did taking this apart; this one didn't work and had infinite resistance, so I just cut 'er open. I think the pictures are self-explanatory. If you need clarification on anything, please ask. Also, I have not had this in an engine yet. My neighbor who is an electronics expert hooked this sensor up to his variable power supply and a scope. It puts out the same signals as a known good stock sensor, except as I said before, they are a bit better defined. After all I have been through with this, I am certain it would work in a car. I will definitely try it sometime down the line, but for the immediate future, I am sick of draining the coolant and buying antifreeze.
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Old 08-06-2017, 10:59 AM   #11
tubman
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Default Re: I now have TWO temperature gauges

Here are some more pictures, including the repaired unit assembled, and a good unit showing the crimps that should be removed with more care than I exercised. Also, you should be able to see the adjusting screw on the closeup of the bi-metal strip on the previous post.
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File Type: jpg IMG_0952.jpg (40.0 KB, 136 views)
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Old 08-06-2017, 11:09 AM   #12
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Default Re: I now have TWO temperature gauges

Thanks, I've never had one apart. Interesting to see the guts.
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Old 08-06-2017, 10:02 PM   #13
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Default Re: I now have TWO temperature gauges

tubman .... Sounds like you did exact what I did on my '47. The driver's side sensor was messing-up the dash gauge readings. So I kept the OE passenger side sensor and by-passed the OE driver's side sensor. Dash gauge has thereafter read good. I then substituted the driver's side sensor with a mechanical gaugse system.

I then tested the actual temperatures around the mechanical gauge sensor and found the mechanical gauge was very accurate. So I removed the OE dash gauge from its setting and using jumper wires, with the engine running at normal temp, I adjusted/calibrated the dash gauge so it read at its center/normal point. The dash gauge was pretty close to normal and just needed a nudge to match the mechanical "normal.' Just have to be careful not to ground any of the electrical contacts while doing the calibration.
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Old 08-07-2017, 02:18 AM   #14
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Default Re: I now have TWO temperature gauges

Drbrown - It sounds like we both have the same setup. I do have extra two terminal sensors that I could put in to get back to completely stock, but I think I'll leave it the way it is for now.

BYW, my dash temperature gauge seems to react much quicker than the mechanical one. After startup, the dash gauge is at quarter scale when the mechanical gauge is still on the peg (100 degrees).
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Old 08-07-2017, 03:18 AM   #15
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Default Re: I now have TWO temperature gauges

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Originally Posted by tubman View Post
Drbrown - It sounds like we both have the same setup. I do have extra two terminal sensors that I could put in to get back to completely stock, but I think I'll leave it the way it is for now.

BYW, my dash temperature gauge seems to react much quicker than the mechanical one. After startup, the dash gauge is at quarter scale when the mechanical gauge is still on the peg (100 degrees).
Heater side if open flow may heat up a bit slower...or just the meters being different.
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Old 04-23-2020, 05:42 PM   #16
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Default Re: I now have TWO temperature gauges

Thanks Tubman for sharing your knowledge and showing us how to rebuild one.
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