Gauges

[difrangia]

When I studied the fuel gage system on our 320 several years ago seems that I finally determined that the Datsun & Nissan vehicles from the 60's to at least early 90's are 0-ohms at empty and 90-ohms at full. GM vehicles were the same from mid-60's to mid-90's. Here's link to a site to study a bit.

 

I ended up with a new sender from Classic Instruments model # SN38T6 that is a direct bolt into the 320 tank. Beauty of the unit is that it doesn't have the float out  on a arm to bounce around. Float is inside the tubular body of the sender. Tiny little hole in lower and upper area of tube maintains the fuel level inside the tube. The sender is about a hundred bucks.

 

https://www.tanksinc.com/index.cfm?ptype=results&category_id=159&mode=cat

 

[datzenmike]

22 minutes ago, difrangia said:

When I studied the fuel gage system on our 320 several years ago seems that I finally determined that the Datsun & Nissan vehicles from the 60's to at least early 90's are 0-ohms at empty and 90-ohms at full.

 

 

That's not been my experience Charlie. At least not with the 620 and 720 senders. The '84 720 FSM says 10 ohms full and 80 ohms empty. I've used a 720 tank and sender on my 620 truck gauge and it read perfectly the same.

[Rusty Dawg]

9 hours ago, datzenmike said:

It's ok if that was sarcastic. It's maybe helpful for someone else searching and reading about the sender/gauge but doesn't want to ask.

You don't know me, but that was 100% sarcasm.

[Stoffregen Motorsports]

I believe Steve is correct. When I swapped in a Smiths gauge in my 320, I thought I remember that the sweep was o=empty.

[Rusty Dawg]

My question now is, did anyone with knowledge about reading ohms look at my photos of the readings at "full"?  That would tell me which direction to go with in purchasing a gauge.  I have had similar dialogue on an old Dodge forum when dealing with an old fuel gauge on a truck.  It seems to be a confusing and/or maybe a complex system understand.

Edited December 14, 2021 by Rusty Dawg

[Stoffregen Motorsports]

I did not open the files to look at the pics. Was the reading high at full and low at empty?

[Rusty Dawg]

13 minutes ago, Stoffregen Motorsports said:

I did not open the files to look at the pics. Was the reading high at full and low at empty?

The tank is full when I took the readings.  I am just not sure how to check the ohms as you will see in the photos.

[stevecar]

The pictures showed up as .HEIC files. Not familiar with that extension. I suggest that you repost them as .JPG to make it easier for people to see.

[datzenmike]

2 hours ago, Stoffregen Motorsports said:

I did not open the files to look at the pics. Was the reading high at full and low at empty?

 

I don't open mystery files either.

[difrangia]

 Whatever  the sender is out of, if you have the sender in hand, take the cover off if necessary (it is on 320 sender as the resistance coil is inside the casting cavity) and take a look at the resistance coil. One end of the resistance coil will connect to the non-ground terminal of the sender and the other end terminates out in space. When the contact that is moved by the float is nearest the terminal end, that's zero or few ohms. When the contact is at the end of the coil furthest away from the terminal that is the high resistance position which is where the 320 sender is when the float is at the highest position in the tank.

 

I did go through the effort to locate the correct resistance wire and rattle-can insulating enamel and re-wind one sender which worked. The gage has to match the sender in polarity and resistance for accurate reading. I'm not sure if reversing the polarity of the vehicle, and many 320's have been reversed, will affect the gage reading. Mine has been reversed and reads correct empty/full direction.

[Stoffregen Motorsports]

If the sending unit is resistance to ground, would reversing the polarity affect the reading? I don't think so.

 

Not sure how the gauge will respond, but the sending unit shouldn't care.

[difrangia]

2 hours ago, Stoffregen Motorsports said:

If the sending unit is resistance to ground, would reversing the polarity affect the reading? I don't think so.

 

Not sure how the gauge will respond, but the sending unit shouldn't care.

 

Electricity is my weak point, but all you say sounds correct to me, Matt.

[Rusty Dawg]

12 hours ago, stevecar said:

The pictures showed up as .HEIC files. Not familiar with that extension. I suggest that you repost them as .JPG to make it easier for people to see.

Ya, sorry about that.  My kids got me a MacBook recently and it automatically converts photos on my phone into a .HEIC file when I AirDrop them.  I don't blame you for not opening them.  Let me work on that so you can see what I see.

[Rusty Dawg]

How's this?  These are readings I took at the base of the stud going to the sending unit.   Was I to use the red probe or the black one?  I will follow with 2 more photos of readings on the outer part of the same stud past the nut holding the wire in place.

 

 

[Rusty Dawg]

2nd readings.  Shouldn't I be getting the same reading regardless of where I check it?

 

[Rusty Dawg]

On 12/8/2021 at 6:34 PM, Rusty Dawg said:

 

IMG_5097.HEIC 2.74 MB · 0 downloads

This is fitting I plan to use to install the temp gauge.  This photo is of fitting on the (cracked) head that was on my truck when I bought it.  The tube will have to be no more than 3/8" thick with standard thread size of 5/8".  I will in fact go with teflon on both.

 

 

JPG file instead...

 

[stevecar]

41 minutes ago, Rusty Dawg said:

How's this?  These are readings I took at the base of the stud going to the sending unit.   Was I to use the red probe or the black one?  I will follow with 2 more photos of readings on the outer part of the same stud past the nut holding the wire in place.

 

 

 

Much better with the jpgs. You have the meter set up correctly. For measuring resistance,  it doesn't matter which one you have the red probe on vs the black probe. Sometimes it would, like if there are solid state devices involved, but here it should just be a rheostat.You should disconnect the lug on the stud to isolate the fuel sender and repeat your measurements. Try to get a good ground with one of the probes.

[stevecar]

37 minutes ago, Rusty Dawg said:

This is fitting I plan to use to install the temp gauge.  This photo is of fitting on the (cracked) head that was on my truck when I bought it.  The tube will have to be no more than 3/8" thick with standard thread size of 5/8".  I will in fact go with teflon on both.

 

 

Be careful when using teflon tape. If you are using the stock temp sender, you want the body of the sender to have a good ground.

[Rusty Dawg]

2 hours ago, stevecar said:

Be careful when using teflon tape. If you are using the stock temp sender, you want the body of the sender to have a good ground.

I'm going to remove the stock temp sender and install a mechanical one and thus why I needed the fitting.  The original temp gauge is finicky and I would hate to overheat the engine over a few bucks.  I could also just use ATV on the threads.

Edited December 15, 2021 by Rusty Dawg

[Stoffregen Motorsports]

18 hours ago, stevecar said:

Be careful when using teflon tape. If you are using the stock temp sender, you want the body of the sender to have a good ground.

I use Threebond on fittings. It flows nicely and doesn't affect grounding.

 

On that fitting, I don't think you need any sealant at all though. Doesn't it bottom out and tighten onto a machined surface inside the thread? I think so. Maybe the sender inside the adapter needs sealant, but not the outer adapter.

[difrangia]

If Rustydawg is using a mechanical (capillary-tube) heat gage the grounding issue will not need to be considered. 

[Rusty Dawg]

36 minutes ago, Stoffregen Motorsports said:

I use Threebond on fittings. It flows nicely and doesn't affect grounding.

 

On that fitting, I don't think you need any sealant at all though. Doesn't it bottom out and tighten onto a machined surface inside the thread? I think so. Maybe the sender inside the adapter needs sealant, but not the outer adapter.

I have yet to thread it in all the way, but it very well could bottom out.

Edited December 15, 2021 by Rusty Dawg

[Rusty Dawg]

Sooooooooo, I removed the lug, topped off the fuel tank and checked the ohms once again.  It bounce around 4.6 to 4.9 on my meter.

[datzenmike]

Which is 10 or less and that produces a full scale reading on the gauge.

[stevecar]

If you have a full tank, the 320 sender should read around 90 ohms. You might want to pop out the sender and take a look at it. I have had good luck rebuilding the senders.

Edited December 16, 2021 by stevecar