Gauges

[Rusty Dawg]

Howdy,

 

I have been looking to replace my gauges in my truck with a mechanical oil and temp gauge and a new electrical fuel gauge.  The original fuel gauge is not functioning, the temp gauge is sporadic in reading the proper temp and the aftermarket oil pressure gauge functions, but I want to replace it.  I do get a reading with my volt ohm meter at the fuel sending unit.  I would like to add a new fuel, oil pressure and temp gauge to mount under the dash to make certain I receive correct readings.  Can anyone enlighten me on what would work on my truck?  

 

I know the temp gauge is currently electrical and I think I would have to find a standard to metric adapter/insert to go into the engine head in order to install a mechanical temp gauge.  The fuel gauge seems to be straightforward since it's electrical.  The oil gauge also seems straightforward since it already has one, although I am not certain why there is an electrical connection attached to where the oil line goes into the engine block.  Not sure how to explain it, but there is a metal unit that is screwed into the block that has an opening for the oil line and the wire is connected to the top of this unit.

 

Thanks,

Roman

[Stoffregen Motorsports]

I used retro Smiths gauges on my 320. Not bolt in, but were period correct.

 

[nicklp]

Oil line to the gauge and electrical for the idiot light? (Above/between speedo and water temp on gauge cluster).

[thisismatt]

Why do you want to use a mechanical oil pressure gauge? If you do, make sure you get a quality braided line and not that crappy plastic one that breaks and sprays oil all over your engine bay or shins 😆

Edited October 17, 2021 by thisismatt

[datzenmike]

Realize that the mechanical reads almost instantly and gives startling numbers. Pressure rises and falls with RPMs like the tachometer. Unlike the electrical that is dampened and smooths the sudden spikes. Sudden stops can uncover the oil pick up and zero the gauge something scary to see. It's completely fine just weird.

[Stoffregen Motorsports]

9 hours ago, nicklp said:

Oil line to the gauge and electrical for the idiot light? (Above/between speedo and water temp on gauge cluster).

There was also a Smiths combo oil/water temp gauge installed in the original radio hole. We just didn't move it.

[Rusty Dawg]

So I plan to leave the mechanical oil pressure gauge that is already in my truck and just install a mechanical temp gauge along with a fuel gauge.  I think I know what I am looking for with a mechanical temp gauge, although getting it to properly fit into the J13 might take some research to find proper fittings.  My question is, and I know this will show my ignorance of electrical components, but is there only electrical fuel gauges?  I want to simply wire my existing fuel sending unit to an aftermarket fuel gauge since mine is dead.

 

Roman

[thisismatt]

How will a mechanical temp gauge "transmit" the engine temp to the gauge?

[datzenmike]

Just like the oil pressure but heat causes expansion and the pressure transmitted through a tube to the gauge.

 

 

The fuel gauge sender is most likely 10 ohms or less for FULL and 80 ohms or more for EMPTY. All Nissan sender/gauges I have seen are thus. Your gauge must be within this range to work properly.

[Stoffregen Motorsports]

And some read low to high, while some read high to low, so there's that to look out for too.

 

Take your sending unit out of the tank and grab your multi-meter. Check the ohms at empty, then check them at full. Simple as that.

[Rusty Dawg]

Hey there,

 

Would you have a good source for adapter fittings?  The head on the J13 has a metric fine thread opening for the temp gauge currently and I will most likely have to find an adapter fitting that takes the standard thread from thermostat from mechanical gauge and adapt it to a metric fitting to go into the head.

 

Roman

[Rusty Dawg]

I think I found a solution without having to re-tap the opening into the head using a few adapters.  I was a little worried at first about leaks, but I am not dealing with a high pressure environment and with some black RTV as my friend I think I can make it work. 

[difrangia]

Wrap a band of plumber's teflon tape three layers thick or so around the ferule-like area of the temp sender when you reinstall it. Did the same on the ferule  of the original-type exhaust leadout. Haven't had a leak on either in nearly six years. Fills in any minute gaps that don't contact metal-to-metal and the teflon will stand the heat.

Edited December 8, 2021 by difrangia

[Stoffregen Motorsports]

If it means using more than one fitting to solve the issue, I try to stay away from adapter fittings. If you can find the fitting with the threads you need in one piece, that's great, but it isn't always the case. Summit Racing is my go to for most fiddly bits, but for Euro-centric cars and trucks, Pegasus Racing also has a great supply. Problem is, you usually need to know what the fitting is called to find it. Or you end up searching for a while with multiple search entries before you find it.

 

I doubt the thread on the Datsun cylinder head is metric. Is the original sending unit one piece or does it have a threaded collar that slips over it? If the latter, likely it's 5/8-18 UNF, which is a common size for that type of sender.

 

If it is a one piece unit, it may be tapered thread. If it is tapered, just thread it to NPT and open up many possibilities.

[Rusty Dawg]

 

IMG_5097.HEIC

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.

 

 

Edited December 9, 2021 by Rusty Dawg

[Rusty Dawg]

9 hours ago, Stoffregen Motorsports said:

If it means using more than one fitting to solve the issue, I try to stay away from adapter fittings. If you can find the fitting with the threads you need in one piece, that's great, but it isn't always the case. Summit Racing is my go to for most fiddly bits, but for Euro-centric cars and trucks, Pegasus Racing also has a great supply. Problem is, you usually need to know what the fitting is called to find it. Or you end up searching for a while with multiple search entries before you find it.

 

I doubt the thread on the Datsun cylinder head is metric. Is the original sending unit one piece or does it have a threaded collar that slips over it? If the latter, likely it's 5/8-18 UNF, which is a common size for that type of sender.

 

If it is a one piece unit, it may be tapered thread. If it is tapered, just thread it to NPT and open up many possibilities.

This is what is installed on my engine currently.  I thought everything on this Datsun J13 engine was metric, but I shouldn't have assumed.

[Stoffregen Motorsports]

Datsun didn't go metric until the '70s.

 

The sending unit you have there looks like the two piece variety. I would search for a 5/8-18 fitting. Actually, if you have a 5/8" fine thread bolt laying around, give that a try before you buy any fittings.

[Rusty Dawg]

I'll start by saying that I am not very well versed with electrical components.  I thought I would simply just check the ohms on my sending unit while the tank was full to get a reading and I am not even certain how to properly do so.  In these photos I checked the ohms with both black probe and then the red probe on the outside of the nut that is on the stud leading to the sending unit with 2 different readings.  I will also attach photos on another post of readings that I took using both probes, but this time I checked at the base of the stud going into the sending unit.

 

IMG_5135.HEICIMG_5134.HEIC

[Rusty Dawg]

Shot of ohms reading at the base.  

IMG_5132.HEIC IMG_5133.HEIC

[datzenmike]

 I think all Nissan gas tank senders/guage units are basically the same, after all, why reinvent the wheel for every vehicle. You could use the same sender and use different length floats. I've used 720 tanks on a 620 and noticed it read perfectly. I have advised others with after market gauges compatibility and have not heard that the advice was incorrect.

 

Datsun/Nissan gas tank senders as far as I know reading 0 to 10 ohms produces a FULL reading on the gauge. 25 ohms is approximately 3/4 full, 37-40 ohms is 1/2 full, 55 ohms is 1/4 full and 80 or more amps reads EMPTY.

[Rusty Dawg]

1 hour ago, datzenmike said:

 I think all Nissan gas tank senders/guage units are basically the same, after all, why reinvent the wheel for every vehicle. You could use the same sender and use different length floats. I've used 720 tanks on a 620 and noticed it read perfectly. I have advised others with after market gauges compatibility and have not heard that the advice was incorrect.

 

Datsun/Nissan gas tank senders as far as I know reading 0 to 10 ohms produces a FULL reading on the gauge. 25 ohms is approximately 3/4 full, 37-40 ohms is 1/2 full, 55 ohms is 1/4 full and 80 or more amps reads EMPTY.

So what I need to find is a gauge that has a range from 0-10 ohms FULL and 80 or more ohms empty, correct?  I've seen some that read up to 240 empty.  I need to stick closer to the ranges you speak of or not?  Sorry, but I just don't understand this very well.  I actually have a 1947 Dodge 2 ton Dodge that took me 10 years to complete and make road worthy and although everything works, I been trying for 2 years to get the fuel gauge to work after sending it off to get rebuilt.🤯  

Edited December 12, 2021 by Rusty Dawg

[datzenmike]

Simply put power is supplied to and through the gauge. The other wire goes to the sender unit in the tank which is grounded. The lower the resistance the more current will flow through the gauge and it will read higher. Anything lower than 10 ohms resistance and the gauge reads maximum or full. As the gas is used up the sender's resistance increases, the current decreases and the gauge reading drops. At 80 ohms (or more) the gauge reads empty. 

[Rusty Dawg]

Thanks for dumbing it down for me😂

[datzenmike]

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.

[stevecar]

22 hours ago, Rusty Dawg said:

So what I need to find is a gauge that has a range from 0-10 ohms FULL and 80 or more ohms empty, correct?  

A 320 fuel sender reads high when full and low when empty. The opposite of the later senders.