Water temp sender units
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Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
Water temp sender units
anyone know what the typical ohm range is for a water temp sensor?
my gauge is off over 15 degrees and the vendor is silent on the problem.
I have a bunch of senders that I can test, just trying to figure out what I am testing for.
I can heat some water to a known temp, and then connect to the gauge lead (and ground) and see what happens..
is this a 5 ohm range, or a 500 ohm range?
Sam
my gauge is off over 15 degrees and the vendor is silent on the problem.
I have a bunch of senders that I can test, just trying to figure out what I am testing for.
I can heat some water to a known temp, and then connect to the gauge lead (and ground) and see what happens..
is this a 5 ohm range, or a 500 ohm range?
Sam
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Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
Sam
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From: Kansas City area
Sam, I don't know the answer to your question but I have had really good tech help from Classic Instruments when I've had a problem. Of course I was using their instruments but i think they would help you also since they are really good folks. If you care to check with them the number is 800-575-0461 and tell them a satisfied customer suggested you call. They have always demonstrated the attitude that if they help a hot rodder, even if not a customer, perhaps they will gain a new customer. Good luck with the frustration.
Hotshot
Joined: Oct 2004
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From: Durham NC
Sam, many temp gauges are just idiot lights disguised as a gauge. As such the available senders may/likelyto not be linear in their "message" to the gauge but are only checked at 3 points: cold; normal operating range; and >boiling. Why do you need high accuracy, just recalibrate the gauge to those temps by swapping out senders until you find one you are happy with, or just by knowing what the gauge you have reads at operating temp?
NOTE: many gauge problems can be traced back to a well meaning installer using teflon tape on the sending unit's threads. Sending units should be installed "dry". The other common issue is an air bubble trapped around the sender's sensor giving a false reading. You might try bleeding the sensor with the water pump circulating water, loosen it until it "weeps" for ~ 30 sec then retighten.
NOTE: many gauge problems can be traced back to a well meaning installer using teflon tape on the sending unit's threads. Sending units should be installed "dry". The other common issue is an air bubble trapped around the sender's sensor giving a false reading. You might try bleeding the sensor with the water pump circulating water, loosen it until it "weeps" for ~ 30 sec then retighten.
Thread Starter
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Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
Sam, many temp gauges are just idiot lights disguised as a gauge. As such the available senders may/likelyto not be linear in their "message" to the gauge but are only checked at 3 points: cold; normal operating range; and >boiling. Why do you need high accuracy, just recalibrate the gauge to those temps by swapping out senders until you find one you are happy with, or just by knowing what the gauge you have reads at operating temp?
NOTE: many gauge problems can be traced back to a well meaning installer using teflon tape on the sending unit's threads. Sending units should be installed "dry". The other common issue is an air bubble trapped around the sender's sensor giving a false reading. You might try bleeding the sensor with the water pump circulating water, loosen it until it "weeps" for ~ 30 sec then retighten.
NOTE: many gauge problems can be traced back to a well meaning installer using teflon tape on the sending unit's threads. Sending units should be installed "dry". The other common issue is an air bubble trapped around the sender's sensor giving a false reading. You might try bleeding the sensor with the water pump circulating water, loosen it until it "weeps" for ~ 30 sec then retighten.
the supplied sender is 675 ohms cold.. one of the VDO senders I have is 700ohms cold. others are 250, 2500 and 2800ohms cold.
I'm not goin for 'high' accuracy.. just wanting the gauge to look 'normal' at normal temps, not all the way over into the danger zone.. (when its not)..
Sam
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Joined: Oct 2004
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From: Durham NC
Then you need to check resistance at operating temp (200 -215) and choose the one that give a gauge reading you can live with. Cold reading is immaterial since the gauge will always read zero with any resistance > threshold of the gauge. I believe the resistance decreases as the sender heats up, so 0 ohms = full scale.
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Hotshot
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From: Pflugerville, tx
Then you need to check resistance at operating temp (200 -215) and choose the one that give a gauge reading you can live with. Cold reading is immaterial since the gauge will always read zero with any resistance > threshold of the gauge. I believe the resistance decreases as the sender heats up, so 0 ohms = full scale.
maybe I can find a 700->0 pot or varistor. to see what the gauge likes..
Sam
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Joined: Oct 2004
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From: Durham NC
That would also tell you if the guage is faulty or not' if it goes full scale with a relatively high resistance and all the senders read much lower when hot you might have a problem.
The gauge suppliers are just buying the mechanisms for a manufacturer and putting their face on them, they likely have no real idea of the specs or even the quality of it, unless they get a lot of complaints/returns..
A last resort would be to take the glass off it and reposition the needle.
The gauge suppliers are just buying the mechanisms for a manufacturer and putting their face on them, they likely have no real idea of the specs or even the quality of it, unless they get a lot of complaints/returns..
A last resort would be to take the glass off it and reposition the needle.
Postmaster
Joined: Jun 2004
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From: Riverside, So Cal
You might also just put a resistor in the line from the sender. They are very inexpensive and you can get variable ones from Radio Shack. If you used a thermometer in the radiator fill and then adjusted the variable resistor so that the gage read the same at running temp, you could dial it in close enough for government work. 
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From: Pflugerville, tx
sam
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Hotshot
Joined: Nov 2000
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From: Pflugerville, tx
You might also just put a resistor in the line from the sender. They are very inexpensive and you can get variable ones from Radio Shack. If you used a thermometer in the radiator fill and then adjusted the variable resistor so that the gage read the same at running temp, you could dial it in close enough for government work.
sam
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From: Westminster,Md
All good info.. I keep a 10k variable pot in my tool box just for these kind of situations (3-leg,available at most Radio Shacks),It has met all my general needs thus far, the 1k "may" work..but why limit yourself or the tool or application when making the purchase?..or keep more than one in the box ..??
It's pretty common practice to add a little resistance in a circuit if nec if..,taking it away is trickier..this is where a lower than required sending unit comes in handy..you just add the right amount of resistance to dial it in..choice is yours to mess with the gauge..or the sender.So ..everybody is right!
I'm generally lazy so this is what I would do..stick the variable resistor(pot) in -line, find out where you and your gauge are happy,read it with a "digital-multimeter",get the number and visit Radio Shack......
It's pretty common practice to add a little resistance in a circuit if nec if..,taking it away is trickier..this is where a lower than required sending unit comes in handy..you just add the right amount of resistance to dial it in..choice is yours to mess with the gauge..or the sender.So ..everybody is right!
I'm generally lazy so this is what I would do..stick the variable resistor(pot) in -line, find out where you and your gauge are happy,read it with a "digital-multimeter",get the number and visit Radio Shack......
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Joined: Jul 2006
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From: Westminster,Md
Your challenged.???..well... I don't know what the 3rd leg is for..??
I've had this thing in my box for 20 yrs and only use 2 of the 3 (soldered leads/clips for easy/quick connection)..I don't build'em.., I just use the stuff Lol! somebody smarter than me has to answer that one. You dont "need" the third leg..it just came that way. But you did get my curiosity up ..so I measured it.
Ground is the center leg (or common position 2),The 1st to center is 0 to 10k ohm, 3rd to center iis just the opposite 10k to 0 ohm. Your potentiometer choice leg configuration may vary, no warranty implicitly implied, see you local dealer for details...Lol!
Your on it,Good Luck!
I've had this thing in my box for 20 yrs and only use 2 of the 3 (soldered leads/clips for easy/quick connection)..I don't build'em.., I just use the stuff Lol! somebody smarter than me has to answer that one. You dont "need" the third leg..it just came that way. But you did get my curiosity up ..so I measured it.
Ground is the center leg (or common position 2),The 1st to center is 0 to 10k ohm, 3rd to center iis just the opposite 10k to 0 ohm. Your potentiometer choice leg configuration may vary, no warranty implicitly implied, see you local dealer for details...Lol!
Your on it,Good Luck!