12v gas gauge

zeke57 · Post by **zeke57** » Wed Jan 30, 2019 12:13 pm

Now that I have decided to convert to a 12v system I am wondering about the gas gauge specifically the sending unit. Is there a way to convert a 24v sender to 12v or is there a 12v sender on the market that will bolt into the a1 tank? Thanks.

MarkR1951M38 · Post by **MarkR1951M38** » Wed Jan 30, 2019 12:23 pm

Kaiser Willys has one for $40...

https://www.kaiserwillys.com/category/f ... j-2a-3a-3b

I stuck this in my M38 tank and works great in 12 v.

zeke57 · Post by **zeke57** » Wed Jan 30, 2019 1:25 pm

Thanks for the link Mark.

Post by **wesk** » Wed Jan 30, 2019 11:43 pm

The gage & sender must be mates. Also the civvy sender uses a different mount bolt layout on the tank.

4x4M38 · Post by **4x4M38** » Thu Jan 31, 2019 6:34 am

I believe there is a variant that will screw into the M38 tank correctly.
Whether it is clocked properly in th M38 tank to allow the float to move properly is a question.

I removed a very rusty version of the one in the link above from my M38 fuel tank. Five holes. You just had to turn it to get the pattern to line up.

zeke57 · Post by **zeke57** » Thu Jan 31, 2019 9:36 am

From what I gather the aftermarket sending units will bolt up to the a1 tanks but they will not read correctly. The Kaiserwillys web site mentions lengthening the float rod to make it work correctly. Has anyone done this?

Post by **wesk** » Thu Jan 31, 2019 10:52 am

Let's avoid the confusion of opinioned guesses/assumptions and stick with the facts.

1 - The civvy senders do not match the screw hole pattern in the military tanks (all three of them)!

2 - The fuel sender must mate correctly electrically with the gauge. This requires the normal purchase to be of a set.

3 - There are a few aftermarket fuel gauging systems that are not targeted at any one specific model and have built in adjustability to get the desired travel of the float and fit of the sender.

I would focus on finding a set that can be easily adapted to the required dimensions. To determine those dimensions just measure your existing equipment.

The Marine Industry is a good place to look: https://www.google.com/search?source=hp ... IZ3orlY5ko

Jeff_Lee · Post by **Jeff_Lee** » Thu Jan 31, 2019 11:59 am

I looked long and hard on ebay and found a 12v gas gauge with OD trim AND the all important illumination slits around the inner rim for backlighting. I got lucky and found such a gauge, and got even luckier when I found a sender that would fit my re-pop tank (MD Juan, I think) and operates pretty well with the found gauge. The sender arm didn't have enough swing, so it "shows" empty, before it is. I didn't bother to lengthen the arm, but could have.

My point here is to consider if you want the backlighting as the original M38 uses. If so, remember to look for the all important slits. Most of gauges I see on sold are Chinese or Indian in manufacture, and don't incorporate the slits.

Jeff

Jeff_Lee · Post by **Jeff_Lee** » Thu Jan 31, 2019 12:02 pm

Larger picture. Unfortunately, No maker information on gauge.

Jeff

Jeff_Lee · Post by **Jeff_Lee** » Thu Jan 31, 2019 12:34 pm

I found the box that the 12v OD gas gauge (above photo) came in. I stored the old 24v gauge in it.
When I searched the NSN number 6680-00-177-8260 on Google it came up as:

"GMC M-36 2 1/2 Ton Gas Truck" and was dated in 1984.
The is one (or a 1000!) out there somewhere on a shelf.

Jeff

Post by **wesk** » Thu Jan 31, 2019 1:06 pm

There is a Army TB/ORD 479 dtd 11-21-52 Standardization of M series Gauges that is worth consulting. There is a copy in my photo album: http://www.willysmjeeps.com/v2/modules. ... _album.php

zeke57 · Post by **zeke57** » Fri Feb 01, 2019 9:38 am

Talked to a fuel sender manufacturer and one thing he mentioned was that the sender he has would only read the level in the shallow end of the m38a1 tank which is where the sender is located so does anyone know of a fix for this or do just know when the tank reads empty you still have reserve?

zeke57 · Post by **zeke57** » Fri Feb 01, 2019 9:53 am

Another thing I am wondering is if I cannot find a 12v fuel sender that will read correctly can I just reuse the original 24v sender? I know it will not read correctly but if it gives me an idea of how much or how little fuel is in the tank that is all I am after. Has anyone tried this setup?

Post by **wesk** » Fri Feb 01, 2019 11:52 pm

When I mentioned matched above I was referring to the gauge and sender being matched electrically. These indicating systems are based on resistance (Ohms). A sender that will read 7 ohms empty and 20 ohms filled must be used with a gauge that is wired to read empty at 7 ohms and full at 20 ohms.

If your plan for your jeep is to run it on 12 Volts and find a quantity gauge system that will function adequately I suggest you stop toying with wild ideas for operating any sender with an unmatched gauge. Just buy a universal aftermarket 12 Volt fuel quantity gauge and with electrically matched sender. You just need to insure the sender will fit the tank at the round hole and the reach of the sender arm is adequate for the depth of your tank. A drill will solve any indexing issue with the sender vs the hole in the tank. Then install it and live happily ever after.

he mentioned was that the sender he has would only read the level in the shallow end of the m38a1 tank which is where the sender is located so does anyone know of a fix for this or do just know when the tank reads empty you still have reserve?

The original 24V sender was indexed in the hole so the arm and float would travel top to bottom of the tank. Your job, if you choose to accept it, is to find a sender that has adequate swing height and lateral reach to perform the same arc the original sender did. To do this simply measure the length of the original 24V senders arm and then measure the total travel top to bottom of the float and then note the angle of the arm at full & empty relative to the top flat surface of the tank. Draw a nice illustration of the above dimensions and angles and email them to your possible sender vendors/manufacturers to find what they have that will fit.

zeke57 · Post by **zeke57** » Sat Feb 02, 2019 8:26 am

Thanks for simplifying it for me Wes.