Fuel capacity - M38A1

iamtehcrispy · Post by **iamtehcrispy** » Fri Jul 11, 2014 8:57 am

Short question, what is the fuel capacity in the tank on an M38A1?

I've got a mixed up '52 M38A1 that I have been driving for a couple months now. The thing has been converted and swapped over in a bunch of places. My fuel tank, for instance, only holds 12 gallons. I just had the thing out and cleaned up to remove all the rust and dirt that was sitting in the bottom of the tank. I have read the data plate, the manual I have, and the operator manual from the downloads section. Everything agrees that it should be 17 gallons.

My problem with this, though, is that I can't see where another 5 gallons would squeeze under that seat. Does the listed capacity include 5 gallons in a jerry can on the back?

Imagine my displeasure when I figured I got to about 12 gallons used one day and said "Oh, I have another 5 gallons to go". Oh course, my fuel gauge doesn't work and I was surprised on the side of the road. On the plus side, I have a nicely cleaned tank now.

Thanks,
Andrew

wilfreeman · Post by **wilfreeman** » Fri Jul 11, 2014 9:10 am

Good question. Maybe all the way to the top it will hold 12. I usually fill mine back up when I have about 1 to 2" left in the tank. Fill it up to about half way up the neck. Usually takes about 8 or 9 gal. My tank is an Omix repop.

MODIFIED · Post by **MODIFIED** » Fri Jul 11, 2014 9:48 am

hmm, I doubt one might consider the interpretation of 5 residual gallons residing in the fuel system itself, i.e; fuel bowl, fuel pump and lines.

Perhaps consider the vehicles 5 gallon jerry can capacity were issued to all vehicles and hence included in the tabulated data.

Post by **wesk** » Fri Jul 11, 2014 8:14 pm

The stock M38A1 gas tank is 17 1/2 gallon capacity. You mentioned squeezing under the seat. Do you actually have a CJ5 tank that lays on the flat civvy floor with a capacity of 10 gallons? The correct M38A1 tank fits into an extra deep well that extends way below the floor.

iamtehcrispy · Post by **iamtehcrispy** » Mon Jul 14, 2014 8:03 am

Nope, it isn't flat bottomed. I definitely have that well in the floor and the tank fits into it. Given the amount of other hack jobs on this thing, I probably have some home fabrication tank sitting in there. My tech advisers (read: "father-in-law and his brother") tell me something is odd about the tank, but can't quite figure out what it is. They are going to take a look at a couple others and see if they can spot the difference.

Post by **wesk** » Mon Jul 14, 2014 8:38 am

And you have lifted the tank from the well and confirmed there is an extension of the tank in the well? Or are there 4 blocks of wood hidden under a few years worth of grit and grime in the well supporting the flat tank?

iamtehcrispy · Post by **iamtehcrispy** » Mon Jul 14, 2014 10:37 am

Well. I just ran out an measured the tank. I knew I had the well, since I had the tank out for cleaning. But, the measurements show pretty much what you have in the diagram. Then, because I'm not the trusting sort, I did the math. Given my exaggerated rounding, that tank in the diagram and the one I measured in my jeep should both be about 17 gallons.

I am now completely confused. It's also going to stay that way until I work up the enthusiasm to drain the tank and pay more attention. Last time, I splashed some gas from a five gallon can into it, left the can at least half full (I didn't see how much was in it to start), and filled up at the gas station for 11.25 gallons.

Oh well. At least I proved my jerry can is good this weekend. I'll have a five gallon reserve for next time. Next on the hitlist is probably cleaning up the mess of wiring from somebody converting it to 12V. They cut off all my number tabs from the military harness.

RICKG · Post by **RICKG** » Mon Jul 14, 2014 11:04 am

An incorrect civvy CJ5 fuel pick-up will deny access to the extra fuel in the lower well-just a thought.

cabinfever · Post by **cabinfever** » Sun Aug 10, 2014 10:41 am

Yesterday, I ran out of gas in my M38A1. It was a bit embarrasing as I told my wife before we took off that we had plenty of petrol in the tank. (My fuel gauge does NOT work). I really thought we had enough. I filled the tank on Memorial Day and have driven less than 100 miles.

At any rate, I added exactly 5 gallons of fuel from a gas can. Then drove the 5 miles to town and filled the rest of the tank. The tank took an additional 7 gallons, for a total of 12 gallons. I fill my fuel tank to the top of the neck on the inside. There is still headspace above this fill point, whether its an additional 5 gallons, I'm not sure. But I always stop filling at the inside top of the neck - as the warning says, "Don not overfill, leave room for expansion."