Is the Series 1/2 temperature gauge adjustable?

[BobTR]

I've got a Series 1/2 temperature gauge TC4304/00 and got a new sending unit p/n 52700 from Speedy Spares with the number 3800/00 stamped on it. I'm testing the combination using heated water in a pan with a candy thermometer, and car battery. The gauge is reading about 10 degrees F below what the thermometer is showing. Is it possible to adjust the Series 1/2 temperature gauge to match the temperature of the water?

Here are a few of the test readings:
Room Temperature: sending unit= 318 ohms
Thermometer = 170, gauge = 160, resistance of sender= 43 ohms
Thermometer = 180, gauge = 169, resistance of sender= 35 ohms
Thermometer = 185, gauge = 175, resistance of sender= 32 ohms
Thermometer = 190, gauge = 180, resistance of sender= 29 ohms
Thermometer = 195, gauge = 185, resistance of sender=25 ohms
Thermometer = 190, gauge = 180, resistance of sender= 24 ohms
Thermometer = 210 - boiling, gauge = 205, resistance of sender= 22 ohms

Bob

 

[phyrman]

As the resistance goes down the temp rises. Try a resistor inline from the sending unit
Or just remember that you are 5-10 degrees warmer than indicated

 

[Barry]

I've got a Series 1/2 temperature gauge TC4304/00 and got a new sending unit p/n 52700 from Speedy Spares with the number 3800/00 stamped on it. I'm testing the combination using heated water in a pan with a candy thermometer, and car battery. The gauge is reading about 10 degrees F below what the thermometer is showing. Is it possible to adjust the Series 1/2 temperature gauge to match the temperature of the water?

Here are a few of the test readings:
Room Temperature: sending unit= 318 ohms
Thermometer = 170, gauge = 160, resistance of sender= 43 ohms
Thermometer = 180, gauge = 169, resistance of sender= 35 ohms
Thermometer = 185, gauge = 175, resistance of sender= 32 ohms
Thermometer = 190, gauge = 180, resistance of sender= 29 ohms
Thermometer = 195, gauge = 185, resistance of sender=25 ohms
Thermometer = 190, gauge = 180, resistance of sender= 24 ohms
Thermometer = 210 - boiling, gauge = 205, resistance of sender= 22 ohms

Bob

Bob,

Based on your readings, I think a 120 ohm resistor in parallel with the sending unit will give you close to the correct gauge reading when the thermometer reading is 190 degrees.

If not, we can fine tune based on the results with the 120 ohm resistor.

HTH

 

[BobTR]

Thank you Barry! I'll will have to find a local place that sells resistors. I'm not familiar with how I would wire the resistor in parallel with the sending unit. Would I put a double connector on the sending unit end of the wire that goes between the gauge and sending unit, and then plug one part of the double connector to the sending unit, and then put a wire from the other tab on the double connector over to a ground point? If I'm way off, please explain the best way to wire a resistor in parallel with the sending unit. I appreciate your help!!
Bob

 

[Tom H]

Bob,
I have done extensive testing on one set of SI, SII gauges and also have data from tests done by RootesRacer on this forum. Based on that data I am pretty confident that the SI, II Temp sender should be about 10 or 11 ohms at 212 F / 100 C. I suspect the sender you have may be close to that, but testing over a range of temps in a pan of water gets tricky. The heavy metal sender will respond to temp changes much more slowly than the water and the candy thermometer. Also note that measuring low resistances around 10 ohms and lower requires careful checking to eliminate the resistance of the test leads when doing the tests. The critical temperature is, of course, around the boiling point. I'd suggest repeating your measurement, focusing on getting the best reading you can get at 190 (where the Alpine gauge has a numbered mark. I would expect the sender to be about 17 ohms and the gauge to read 190 when the water is held at about 190 (according to the candy thermometer) for several minutes.

The gauges themselves are adjustable, but I would have more confidence in the original setting from the factory (assuming no one has messed with the adjustment) than any adjustment you (or I) could accomplish. All the calibration of these gauges depends on coils and magnetics which are not very subject to drift over time.

If you do conclude that some resistance in parallel with the sender would achieve better accuracy you can simply install that resistance between the T and E terminals on the back of the gauge while the gauge is out of the car. But that becomes more difficult to change or remove after the gauge is installed in the dash . So I suggest adding it right near the sender. As you say, put a double connector on the sending unit end of the wire. Connect one to the sender and connect the other to one end of the added resistor, Then connect the other end of that resistor to a good ground.

Tom

 

[moonstone SIV]

I've had success adjusting the back of the gauge on a SII Alpine and a SIII Rapier, same gauges. Correct thermostat, sender unit and still the gauge was inaccurate. Adjustment was done hot with a master gauge in the radiator. Some patience required to get the 2 nuts in just the right place in the slots in the back of the housing but it made a difference. Just a thought.

 

[BobTR]

Tom and Moonstone, thank you!! Per Tom's suggestion, I will test again and hold the water temperature at 190 for quite a while to see how the gauge responds and see the resistance reading of the sending unit. I will then also let it boil for a while to determine how the gauge handles that, since that is a crucial reading.
Bob

 

[Barry]

Thank you Barry! I'll will have to find a local place that sells resistors. I'm not familiar with how I would wire the resistor in parallel with the sending unit. Would I put a double connector on the sending unit end of the wire that goes between the gauge and sending unit, and then plug one part of the double connector to the sending unit, and then put a wire from the other tab on the double connector over to a ground point? If I'm way off, please explain the best way to wire a resistor in parallel with the sending unit. I appreciate your help!!
Bob

Bob,

Glad to help (or possibly add confusion).

For testing, the simple approach would be using alligator clips to attach the resistor to the terminals of the sender. To simplify finding the right resistance value, you could use a 1-watt 250 ohm potentiometer (aka variable resistor) to "adjust" the gauge reading at 190 degrees water temperature. Once the gauge is reading correctly, remove and measure the resistance of the "pot" and then source the appropriate 1% fixed resistor.

As Tom H noted, the parallel resistor does not have to be physically located at the sender and there are a couple of options for a permanent wiring setup.

Edited to note that the Alpine sending unit only has one terminal and that the "second terminal" is chassis ground.

Sorry for any confusion.

 

[BobTR]

Today (Sunday) I tested again. I slowly took the water up to 190F. Then I held it (as best I could with an electric hot plate) at 190 for about 20 minutes. Then I took it up to a boil for about 10-15 minutes. At 190 on the thermometer it read about 180+ on the gauge with 27 ohms at the sending unit. I tested the resistance several times during the 20 minutes I had the thermometer around 190 and the resistance was always right around 27 ohms (previous test was 29 ohms) . The thermometer never showed above 210 when the water was boiling vigorously. With the thermometer at 210 the gauge showed about 205 with 25-26 ohms. I was surprised that on my last test at 210F the resistance at the sending unit was 22 ohms, whereas today it was 25-26 ohms and I got that reading several times during the 10-15 minute period when the thermometer was at 210 and the gauge was at 205.

Tomorrow I will try to find some resistors or potentiometer.
Bob

 

[Tom H]

Bob, sounds like your test procedure was pretty solid. Not sure what meter you are using, but what does your meter read when you connect the leads together? Or better yet, when both leads are touching the sender body, i.e. ground. Should read pretty close to 0.1 ohm, not quite zero, just the resistance of the test leads.

I've been trying to get data on these SI, II gauges and senders for years. My only testing so far is on one Temp gauge, plus data from RootesRacer on his one gauge. I'd sure like to find out the factory specs on that sender.

Tom

 

[beamdream]

Bob, sounds like your test procedure was pretty solid. Not sure what meter you are using, but what does your meter read when you connect the leads together? Or better yet, when both leads are touching the sender body, i.e. ground. Should read pretty close to 0.1 ohm, not quite zero, just the resistance of the test leads.

I've been trying to get data on these SI, II gauges and senders for years. My only testing so far is on one Temp gauge, plus data from RootesRacer on his one gauge. I'd sure like to find out the factory specs on that sender.

Tom

Would the Archive centre have this info ?

 

[bernd_st]

Perhaps. The Original Rootes spare part # is P.46371. Worth to check via Matt Ollman...


P.S. The parts list states maker code : TT4800/00 (Smiths)

 

[BobTR]

When I got the 3800/00 sending unit from Speedy Spares in the UK (their p/n 52700) I asked about why I got the 3800/00 instead of the 4800/00. Here is their reply: "Smiths TT3800 and TT4800 are actually interchangeable anyway. They are the same but TT4800 was the number they used in their kits, whereas TT3800 was used for original equipment." Does the Archive centre agree with that?
Bob

 

[Barry]

Please note that I edited post #8 to cover the "single terminal" issue.

 

[bernd_st]

I'm not from the archive but my experience is if it's not explicitely mentioned in the drawings they can't tell. People in the trade may sometimes know better --especially when it comes to compatible parts. If Speedy says so they may be right...

 

[BobTR]

Tom, I have a Cen-Tech multi-tester. I believe I got it at Harbor Freight. It seems pretty good. When I set the resistance dial (ohms) to the lowest setting and touch the leads together I get a reading of .001. When I set the dial to 200 ohm mark, I get 00.4. When I set it to the 2k mark on the dial, I get a reading of .000. I used the 2k dial setting in my testing.
Bob

 

[BobTR]

By the way, I'm a bit skeptical of the response from Speedy Spares because pictures that I find on the internet of the TT4800/00 don't look the same as pictures of the TT3800/00. The 4800 has a flat bottom surface that requires a washer to seal against flat surface, whereas the 3800 has a tapered bottom that appears to seal against another tapered surface down in the water jacket.
Here are pictures of the TT3800/00 and then the TT4800/00 from the internet.
Bob

 

[BobTR]

Success with getting the TC4304/00 gauge from Series 1/2 Alpine, and the 3800/00 (52700) sending unit from Speedy Spares working and adjusted to almost the exact correct temperature!! Thank you Barry for suggesting the 120 ohm resistor in parallel and thank you Tom for reviewing my testing procedure and set up. I had to order resistors on-line from DigiKey since I could not find any local stores selling individual resistors. The Application Engineer at DigiKey was tremendous and patient in helping me find the right resistors for the testing I was doing. I ordered 3 resistors and a small potentiometer but I went straight to using the 120 ohm resistor and just used alligator clips to connect it to a parallel wire to the sending unit. The thermometer and gauge showed the exact temperatures all the way from 170 through 205 heating the water very slowly, so I went ahead and soldered the 120 ohm resistor into a wire and hooked it all up again and ran through the test. Again the thermometer and the gauge showed the same temperatures. So I claimed success and installed the 3800/00 sending unit and gauge in my car and went for a test drive. It worked just right. I am posting pictures of my test set up and the resulting thermometer and gauge readings. And the installed sending unit.

Thanks again for all the help from this forum!!
Bob

 

[Tom H]

Great job. Mike Hartman and I have been working on a summary document on the SI,II gauges and I think we need to incorporate your work and data. I only have data taken on the gauges themselves and no sender data, so this may make a lot of sense in our write up.

Tom

 

[Ken Ellis]

During calibration, what was your battery voltage vs. what it is when the car is running? Granted, the only one that matters is voltage when underway -- when you care about a few degrees of temp. on the gauge... Is the SI/SII gauge supply circuit regulated? This testing is great to see, by the way. (Insert "thumbs-up" emoji here.)