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Fuel gauge issue

JEB

JEB

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I'm back with a problem I can't seem to fix on my M38A1.
Fuel gauge still reads 1/2 a tank when full.
So far...
-New sending unit from Midwest Military.
-Re-grounded gauge.
-Correct fuel gauge per Army manual.

Everyone says It's a ohms issue.

How to fix?
Buy every freaking' gauge on the internet until you find correct one?
 
DeetFreek

DeetFreek

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Are you on FB? More specifically, there's a group titled M38/M38A1. I did a quick search and came up with a thread that Wes Knettle commented on, and since he's the closest thing to the Bible, I saved the pics of his replies. If you're not, shoot me a message and I'll send you the TM pages.

Secondly, a lot of guys responded with they bent the float arm until it read correctly.
 
JEB

JEB

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Sorry, I don't do Facebook...
But I do have a TM.

I haven't looked at it thinking the ohms mismatch issue between the gauge and sender would not have happened when everything was new and units were made by OEM suppliers.

Does anyone have any experience with bending the sending unit float arm?
 
m38inmaine

m38inmaine

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You can test it two ways, with or without a multimeter, best to have a meter but let's try a simple test first. Remove the sending unit from the tank, attach a temporary ground wire from the sending unit body to a known good ground on the body, with the sending unit wire plugged in and a temporary ground attached turn on the ignition, with the float hanging down it should show empty, as you slowly raise the float you should see the meter read and all the way raised should show full. If this test works then it is a float level issue and the arm will have to be bent to correct it.

If you have a meter, set it to ohms and with the sending unit removed, no wires attached place one meter lead to where the wire plugs in and one to the sending unit body, as you move the float up you should see a steady increase or decrease in ohms, if I remember I think it goes from 0-60 ohms, the manual will have that info. If this checks out the sending unit is good and you probably have a bad tank to ground issue. It is a very simple system and will be easy to fix once you understand how it works.
 
JEB

JEB

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Colbert, WA
Finally resolved.
It took three tries, but it was firmly re-grounded....
So, it reads fairly accurately (with fuel up to the base of the huge filler neck, it reads a tick below the "full" hash mark)....which I'm told is about as good as a 70 year old Jeep is going to get.
 
Last edited:
JEB

JEB

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Location
Colbert, WA
I didn't Ser what the repair was, I believe he used an extra wire to a good surface.
The gauge works better but still shows about 3/4 of a tank when full.
So whay next adjust the float?
 
JEB

JEB

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Location
Colbert, WA
That's just it, I don't know how accurate ANY would be 70 years on...


Maybe it is as good as its going to get without All new aftermarket gauges...which I don't want.

Why doesn't someone make new gauges that look correct?
 
M

Mud Diver

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Yorba Linda, CA
We may be talking pineapples and oranges. I’m working with 12 volt aftermarket gauges that like correct, but don’t have the windows for the panel lights. Dumb a**s me tossed the 65’ish instruments when I got the new stuff and shit still doesn’t work.
 
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