Temperature gauge
Thread Starter
Racer
Joined: Jan 2004
Posts: 277
Likes: 0
From: Bellevue WA
Temperature gauge
After an all new cooling system in my '63 SW, my temp gauge was reading 200-210 against a 180 gun so I put in a Napa sender that cross referenced to a Wells TU 5 (no Autozones around here) and the gauge now goes to 230-240 against a 180 gun. Can I assume bad gauge, not trust the cross referenced Napa sender or ?
Melting Slicks
Joined: Oct 2001
Posts: 3,025
Likes: 12
From: Pleasant Grove AL
There is still a good chance you don't have a proper sender. If you have a digital ohm meter, check the resistance of the sender at room temp. Should read around 700 ohms or just a bit less.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
You can't tell much from checking the sender's resistance at room temperature; the response curve is exponential, and the acceptance range at room temperature on the original AC drawing is within a band from 550-800 ohms. I haven't heard of anyone who makes a correct reproduction of the original 321 sender, but the TU-5 (or Standard TS-6) seem to be closer than most.
The original AC temperature-vs.-resistance response values for the P/N 1513321 sending unit are as follows (not a linear progression - it's an exponential curve):
100* = 340 ohms
120* = 250 ohms
140* = 180 ohms
160* = 140 ohms
180* = 110 ohms
200* = 85-90 ohms
220* = 65-70 ohms
240* = 50-60 ohms
The original AC temperature-vs.-resistance response values for the P/N 1513321 sending unit are as follows (not a linear progression - it's an exponential curve):
100* = 340 ohms
120* = 250 ohms
140* = 180 ohms
160* = 140 ohms
180* = 110 ohms
200* = 85-90 ohms
220* = 65-70 ohms
240* = 50-60 ohms
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
The users' manual that came with your meter will show you how to set it up for various readings; normally one of the leads has to be moved to a different connection to read resistance (ohms) than the one used for measuring DC volts. 
Melting Slicks
Joined: Oct 2001
Posts: 3,025
Likes: 12
From: Pleasant Grove AL
The 700 +/- ohms resistance at room temp is certainly no guarantee the sender will be accurate in other ranges, but it has been my observation that most senders which are properly calibrated read in the 680-700 range at around 70*. However, you can test one throughout the range by heating in a shallow pot of water with a thermometer for reference. Attach one lead to the case and then touch the other lead to the top pin connector to check the resistance at various temps.
Burning Brakes
Joined: Jul 2003
Posts: 868
Likes: 5
Almost every 63-64 temp gauges that I have serviced have been off that much(210-when actual temp is 180) from the factory.
Even the later replacement gauges were as well.
A 330 ohm resistor across the terminals will fix it.
Jason
VetteInstruments@aol.com
Even the later replacement gauges were as well.
A 330 ohm resistor across the terminals will fix it.
Jason
VetteInstruments@aol.com
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