Sending unit
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More Turbo
Joined: Aug 2009
Posts: 551
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Sending unit
In my 49 I had the thermal switch fail the other day, I had one and remembered I had another set if flathead heads with sending unit/ thermal switch.
i pulled them out and installed into my truck, sending unit worked bit read cooler than it should due to being gunked up. I pulled it today and soaked it in fleet guard restore on stove top at approximately 212f for 90 min. It cleaned it as new looking, but now temp gauge goes all the was to C and doesn’t move until the key is off and goes to H as it should.
Im letting it sit overnight to see if it will work in am, what could have happened cleaning to cause it to fail? I prefer the vintage unit over the reproductions available currently.
i pulled them out and installed into my truck, sending unit worked bit read cooler than it should due to being gunked up. I pulled it today and soaked it in fleet guard restore on stove top at approximately 212f for 90 min. It cleaned it as new looking, but now temp gauge goes all the was to C and doesn’t move until the key is off and goes to H as it should.
Im letting it sit overnight to see if it will work in am, what could have happened cleaning to cause it to fail? I prefer the vintage unit over the reproductions available currently.
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
I don't believe those sending units are actually liquid tight in the first place. Chances are the heating while submerged allowed expansion of the joints and the Fleet Guard leaked in and shorted the contacts. You can try heating again not submerged and see if the liquid seeps out, but I think it's done for.
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
That's a new one on me too. I always assumed they were dry-bulb units considering the electrical components. I wonder what liquid is used that would be non-conductive?
Logistics Pro
Joined: Sep 2014
Posts: 4,920
Likes: 21
From: Bothell & Silverdale, WA
It's been my experience with marine instrumentation that all liquid filled temperature indicators are either direct reading (bulb thermometer) or indirect reading (wet bulb - connects to a gauge via a capillary tube, or a dial indicator via linkage). The bulbs are either directly submerged or installed in a well that is filled with a graphite paste to transfer heat from the well wall to the bulb without any loss. So I'll stand by my original assessment that the sending unit took a big gulp when submerged and heated, and failed. You MAY be able to save it by carefully drilling a pinhole in the top corner of the phenolic cap, hang it upside down and heat it up with a heat gun to see if it will drain.
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hugger94
1987 - 1996 F150 & Larger F-Series Trucks
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May 21, 2009 12:01 PM
