Temp Sending units for ‘73
Thread Starter
Racer
Joined: Jun 2017
Posts: 401
Likes: 79
From: Northeast PA
Temp Sending units for ‘73
Age old story, every new temp sender doesn’t run the gauge correctly. Gauge /wiring is good, every new sender I’ve purchased when I test shows cold resistance way too high, & doesn’t go low enough to even make the gauge move off of cold. I tried the Willcox variable resistor, & that doesn’t help because it’s starting off with excessive resistance & you can’t make it lower that what the senders default resistance is. Lectric doesn’t list a sender for that year, & I’ve tried at least 4 senders from different sources. I’ve become an expert at testing, but at a loss in finding an adequate replacement… As most of you know, Willcox site has been down for about a month, think they went out of business?
Race Director
Joined: Mar 2017
Posts: 11,946
Likes: 4,506
From: Virginia
Have you tried faking a sender with some resistors to make sure it's not a wiring problem?
I dove into the later senders a bit for a DIY trusted gauge. I never found a datasheet for the earlier C3 senders.
I dove into the later senders a bit for a DIY trusted gauge. I never found a datasheet for the earlier C3 senders.
Thread Starter
Racer
Joined: Jun 2017
Posts: 401
Likes: 79
From: Northeast PA
I did use a variable resister to test the gauge/wiring, & I can dial-in any temp I want the gauge to read. I think if it went down incrementally under 50 ohms the gauge would go up to around 200. Now I did that with the cluster out of the car so I suppose theoretically the ohms wire could be suspect, but when in the car & I ground the green ohms wire the gauge pegs to the rivet as the Willcox videos show.
Race Director
Joined: Mar 2017
Posts: 11,946
Likes: 4,506
From: Virginia
Here's the sensor I used for my DIY sensor setup. I have an Arduino reading a voltage divider circuit. I could not find an equivalent datasheet for the stock early C3 sensor. Perhaps the Wilcox site hosted that information, when it was up.
FWIW, this sensor is about 220 Ohms at 200 F, and 50 Ohms is 293 F.
Direct link to a PDF, if it doesn't work, it is a Delphi Coolant Sensor, GM part number 12146312. This is not what is in your car, but is (I think) used by the ECM in 82 C3s, and perhaps even in 81. The part numbers are all over the place, but I doubt the temperature response curve changes. I really wish I could find the curve for the stock sensor. Perhaps I'll have to measure mine.
https://pe-ltd.com/assets/coolant_temp.pdf
FWIW, this sensor is about 220 Ohms at 200 F, and 50 Ohms is 293 F.
Direct link to a PDF, if it doesn't work, it is a Delphi Coolant Sensor, GM part number 12146312. This is not what is in your car, but is (I think) used by the ECM in 82 C3s, and perhaps even in 81. The part numbers are all over the place, but I doubt the temperature response curve changes. I really wish I could find the curve for the stock sensor. Perhaps I'll have to measure mine.
https://pe-ltd.com/assets/coolant_temp.pdf
Thread Starter
Racer
Joined: Jun 2017
Posts: 401
Likes: 79
From: Northeast PA
Since my C3 is a 73 that sensor won't work, nor fit the heads. I recall seeing the Willcox resistance vs temp tables, testing 3 different senders, with the highest resistance at 60 degrees being about 600 ohms, the two others were a little lower than that... the one I just received is at 2.3k ohms, & the one before that was >6k, the resistance on neither of those senders drops below 1100, so the gauge stays put at full cold. I put them in hot water & read resistance as off the laugh meter.
Race Director
Joined: Mar 2017
Posts: 11,946
Likes: 4,506
From: Virginia
Since my C3 is a 73 that sensor won't work, nor fit the heads. I recall seeing the Willcox resistance vs temp tables, testing 3 different senders, with the highest resistance at 60 degrees being about 600 ohms, the two others were a little lower than that... the one I just received is at 2.3k ohms, & the one before that was >6k, the resistance on neither of those senders drops below 1100, so the gauge stays put at full cold. I put them in hot water & read resistance as off the laugh meter.
I wish I could find the same for the previous sensor. Perhaps I'll just have to measure mine. It is a big frustration to me that most sites just say "this is the part you need", without a link to a datasheet. Hopefully the Willcox site comes back online.
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
Per GM Parts WKI the sender number for 73-74 is 6490453.
See this for reference: http://gmpartswiki.com/getpage?pageid=97253
Per Corvette Central the equivalent they sell for that GM part number is their Part # 303586. They even cross reference it to the GM part number:
See here for that info: https://www.corvettecentral.com/c3-6...d%26q%3d303586
Since you already have the adjustable resistor, and you state that your wiring is satisfactory, then you should be able to dial this in...assuming your gauge is good.
I have the Willcox adjustable resistor in my 68 and it works lke a dream.
See this for reference: http://gmpartswiki.com/getpage?pageid=97253
Per Corvette Central the equivalent they sell for that GM part number is their Part # 303586. They even cross reference it to the GM part number:
See here for that info: https://www.corvettecentral.com/c3-6...d%26q%3d303586
Since you already have the adjustable resistor, and you state that your wiring is satisfactory, then you should be able to dial this in...assuming your gauge is good.
I have the Willcox adjustable resistor in my 68 and it works lke a dream.
Age old story, every new temp sender doesn’t run the gauge correctly. Gauge /wiring is good, every new sender I’ve purchased when I test shows cold resistance way too high, & doesn’t go low enough to even make the gauge move off of cold. I tried the Willcox variable resistor, & that doesn’t help because it’s starting off with excessive resistance & you can’t make it lower that what the senders default resistance is. Lectric doesn’t list a sender for that year, & I’ve tried at least 4 senders from different sources. I’ve become an expert at testing, but at a loss in finding an adequate replacement… As most of you know, Willcox site has been down for about a month, think they went out of business?
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Race Director
Joined: Mar 2017
Posts: 11,946
Likes: 4,506
From: Virginia
Per GM Parts WKI the sender number for 73-74 is 6490453.
See this for reference: http://gmpartswiki.com/getpage?pageid=97253
Per Corvette Central the equivalent they sell for that GM part number is their Part # 303586. They even cross reference it to the GM part number:
See here for that info: https://www.corvettecentral.com/c3-6...d%26q%3d303586
Since you already have the adjustable resistor, and you state that your wiring is satisfactory, then you should be able to dial this in...assuming your gauge is good.
I have the Willcox adjustable resistor in my 68 and it works lke a dream.
See this for reference: http://gmpartswiki.com/getpage?pageid=97253
Per Corvette Central the equivalent they sell for that GM part number is their Part # 303586. They even cross reference it to the GM part number:
See here for that info: https://www.corvettecentral.com/c3-6...d%26q%3d303586
Since you already have the adjustable resistor, and you state that your wiring is satisfactory, then you should be able to dial this in...assuming your gauge is good.
I have the Willcox adjustable resistor in my 68 and it works lke a dream.
Lectric Limited sells them, too.
https://www.lectriclimited.com/tempe...ng-unit-117238
And I quote:
Originally Posted by Lectric Limited's Website
Lectric Limited·s exclusive temperature sending units are NOT generic replacements. They have been manufactured in strict accordance to the original manufacturer·s blueprint specifications and tolerances.
Also, potentially of note:
Originally Posted by Lectric Limited's Website
Unless necessary to prevent leaking, we recommend that you do not use Teflon· tape, pipe compound, or any other sealant when installing this sending unit. Simply screw it in. Adding anything onto the sending unit's threads may result in improper operation.
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
Good find.
And lectriclimited agrees with the Corvette Central & GM wiki part number cross-referencing.
https://www.lectriclimited.com/catal.../category/734/
I will add that I use NeverSeize on my temp senders. It is conductive and makes things easier if I need to remove
And lectriclimited agrees with the Corvette Central & GM wiki part number cross-referencing.
https://www.lectriclimited.com/catal.../category/734/
I will add that I use NeverSeize on my temp senders. It is conductive and makes things easier if I need to remove
Thread Starter
Racer
Joined: Jun 2017
Posts: 401
Likes: 79
From: Northeast PA
Thanks for all of your feedback… The other item, that I just happened to realize is that the motor is not original, was replaced with another 350 that the prior owner didn’t know what year it was, nor if it even was from a Corvette. Numbers indicate it’s from 72 or 82, and the the heads accept a 3/8” NPT & the stock 72 sender seems to be 1/2” according to Lectric.
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
Ok then... I know of a 3/8" sensor that you can dial in to read accurate at 180°F. But anywhere beyond that and it deviates too dang much to be useful. Let me get that for you. At least you'll know that temperature....gimme a sec.
Thanks for all of your feedback… The other item, that I just happened to realize is that the motor is not original, was replaced with another 350 that the prior owner didn’t know what year it was, nor if it even was from a Corvette. Numbers indicate it’s from 72 or 82, and the the heads accept a 3/8” NPT & the stock 72 sender seems to be 1/2” according to Lectric.
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
It would probably be easy enough to get a 3/8" male to 1/2" female adapter and just use the specified sensor...... as long as it is deep enough for the sensor to fit....but meanwhiler......
Here. Read this. Duralast TU66 Temp Sender.
I was able to dial it in at 180°F but it deviates a lot either below or above that...... you can read the rest of the thread if you want to see how wonderful that Willcox adjustable resistor is.....
https://www.corvetteforum.com/forums...post1603572711
Here. Read this. Duralast TU66 Temp Sender.
I was able to dial it in at 180°F but it deviates a lot either below or above that...... you can read the rest of the thread if you want to see how wonderful that Willcox adjustable resistor is.....
https://www.corvetteforum.com/forums...post1603572711
Last edited by carriljc; Jun 21, 2022 at 01:24 AM.
Melting Slicks
Joined: Apr 2010
Posts: 2,794
Likes: 1,195
From: Canberra Australia
2025 C3 of the Year Finalist - Modified
I tested a number for my 71 a number of years back and found the closest was the WT-203Z
Was doing some more testing today...
https://www.corvetteforum.com/forums...post1605301671
Was doing some more testing today...
https://www.corvetteforum.com/forums...post1605301671
Last edited by CraigH; Jun 21, 2022 at 08:25 AM.