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Temperature transmitter

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53 minutes ago, stevecar said:

That will not matter. If that were true it would work differently with pos vs neg ground.

I have a used tested sender for $50 or new for $100. Still expensive.

Tried that first thing, didn’t work.

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On 2/24/2019 at 10:19 AM, stevecar said:

The 320 and 1500 temp sender is a mechanical device that is either on or off depending on the bimetallic reeds being open or closed. It has the effect of supplying a higher average voltage across the gauge when it is cold, which is the opposite of the newer types. It has nothing to do with positive or negative ground.  I do not know of any equivalent senders.

So it's on or off with no variance in resistance?

 

If you are dead set against purchasing the new OEM part, then you've got some homework to do. Get out your multi-meter, boil a pot of water and dunk whatever sender you have in and take some readings. If you say the 510 sender causes the gauge to read backwards, does it at least have a similar range? If you can figure out the resistance range, then you at least have something to go on.

 

Another approach is to buy yourself a volume knob for a guitar amp and wire it in place of the gauge sender wire (one side to ground) and start turning the knob. If you can get the gauge to move, then get it to either end of the range. Once there, take a resistance reading and write it down.

 

With this knowledge, you can then start the hunt for a sender with a similar range going the same direction. Now, once you find a sender, even if it does not have the same mounting style, you may be able to machine up a bushing that threads into the motor and also accepts the new sender.

 

If you can't find the correct range, you may still be able to adjust the range output with a resistor wired into the system. The guitar amp volumn knob will again help find the correct resistance for the ohm requirements of the resistor.

 

I've gone through this many times during my engine swap jobs and I have never come across a gauge that I couldn't make work with a different sending unit. Here is a worst case scenario: you get the gauge working but in the opposite direction. Simply remove the gauge from the cluster and paint on a new scale. Not original, but who would know?

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Taking a step back...

 

If I had to go through all of this just to save $150...? I would just buy the OEM part.

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Usually.... the gas and the temp gauges are powered by a small 8? volt thermal/mechanical regulator so that the varying 12.6-14.5 supply when running or not does not cause the gauge to read higher or lower. Most Datsuns are this way. I assume the gauges are similar and just have different markings. What I do know is the resistance range for the later 521/620/720 (probably all Datsuns) is 0 to 80 ohms. From this it could be assumed that the temp senders are also 0 to 80 ohms to move the gauges, regardless of whether gas or temp, through the same distance range using the same 8? volts. 

 

I'm saying the 320 gas and temp senders are probably the same resistance range... what ever that resistance is.

 

So. You used a 510 sender? or L16 sender? and the 320 uses a two wire? Have you tried the other wire.

Does the gauge read in the middle range, you didn't say, only that it read upside down or opposite.

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320 fuel gage and sender are:

 

0 Ohms = Empty

90 Ohms = Full

 

Same as most GM in Mid-60's to Mid 90's.

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On 2/24/2019 at 11:19 AM, stevecar said:

That will not matter. If that were true it would work differently with pos vs neg ground.

I have a used tested sender for $50 or new for $100. Still expensive.

Steve,

I’d like to buy the used tested sender you have. How would you like payment? I can do PayPal, Western Union, certified check, whatever.

My e-mail is dwightrutherford@hotmail.com

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22 hours ago, Stoffregen Motorsports said:

So it's on or off with no variance in resistance?

 

Correct. It is not like the fuel gauge sender, which varies resistance depending on position.

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Interesting. So how does an on/off switch tell the gauge to read anything other than on or off?

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6 minutes ago, stevecar said:

 

Correct. It is not like the fuel gauge sender, which varies resistance depending on position.

I am confused. If it is an on-off switch, how does the needle on the gauge know where to be?

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It will change from on to off at different rates, depending on temperature. The way it works is that the contacts are together when cold. That is why the temp gauge will go towards zero when you turn your key on. After the current flow through the contacts heats one of the bimetallic reeds enough, it will open and the temp gauge will start to go back to the hot position. Without current flowing through it, the reed will then cool down until it makes contact again. Then the whole process starts over. Once going it will change states at a rapid rate and will stabilize, depending on the temperature. The average voltage supplied to the gauge is what is important.

I should have put this explanation out earlier, but was trying to keep it simple.

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Totally makes sense now. ?

 

Learned something today.

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Ok, makes sense. Thank you for the explanation.

 

I bet a variable resistance sending unit would move the gauge, and it sounds like the 510 sender is already doing just that. So we're back to finding one that moves the needle in the proper direction with a similar range.

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Clear as mud!!!  LOL

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