M38A1 fuel pumps

Custer · Post by **Custer** » Tue Mar 22, 2011 4:30 pm

Wondering about fuel pumps for 52 M38A1, the pump that was on the jeep is not original it has a glass bowl on top, in & out lines on bottom and top.
When I got my jeep he had a 12v electric fuel pump added on so not sure if the one I have is good or not, (jeep is apart for restoration) so was wondering if the aftermarket fuel pump for CJs or M38s work with a 24 volt system.

SteveJ · Post by **SteveJ** » Tue Mar 22, 2011 6:32 pm

Depending on the level restoration you are doing why not just get a rebuilt original mechanical pump then you will be able to hook up the vaccum side for the original wipers

Post by **wesk** » Tue Mar 22, 2011 9:07 pm

so was wondering if the aftermarket fuel pump for CJs or M38s work with a 24 volt system.

I am not sure which pump you are referring to here. The 12 volt electric or the CJ glass bowel mechanical pump.

Either can be made to work with the 24 volt jeep. My personal choice is the same as has already been pointed out. Use the stock pump especially since the vacuum side is needed for proper venting and wiper activity.

If the CJ pump has a vacuum half then it will meet the needs of your stock vent and wiper system.

There are several ways to adapt the 12 volt pump to your 24 volt jeep but you will have no vacuum for the stock system needs.

There are also many choices in 24 volt electric pumps both civilian and military issue.

If you decide on an electric pump be sure to provide a means to cut the pump off in an emergency. Most folks have a on/off switch for the pump in series with an oil pressure switch so the pump will not function when the engine is not running. Then an alternate power source during start so the pump will run when the starter is engaged.

Custer · Post by **Custer** » Wed Mar 23, 2011 8:42 am

Ya the 12 volt electric was fucntional before restoration and it did have a seperate switch to shut down the pump. The aftermarket pumps I saw did have vacum also. I have herd though the advantage to the electric pump is the ethonal fuel problem, you shut the pump of run the carb dry of fuel. Im not even sure wether or not the current pump ( fuel/vacum)works, but I would like vacum for the wipers. So anyway is the running a 90/10 blend
going to be a big deal I'm not going to driving it much when all is done.

Thanks for the info

Post by **wesk** » Wed Mar 23, 2011 9:20 am

Electric pumps have no advantage over mechanical pumps on an M38 or M38A1. They cost more, have pressure regulation issues and are hazardous if not safety switched so they don't continue to run in an accident. Using 12 volt pumps in 24 volt systems creates an unbalance in power consumption between batteries and results in degradation of one battery as opposed to the other.

Ethanol will have the same affect on parts in both electric or mechanical fuel pump installations.

Leaving fuel bowls dry for long periods results in corrosion and loose corrosion particles plugging carb passageways.

The best way to combat the nasty effects of ethanol is to not use it or reduce the percentage of it in your gas and couple this to the use of the most modern rubber parts you can acquire.

The easiest way to reduce the percentage of ethanol in your gas is to mix it with aviation 100 low lead gas at a ratio between 2 to 1 up to 1 to 1.

If you store the jeep for a long period then you can drain all the fuel and pump a very light oil 10 weight or lighter thru the fuel pump and carb. Or run the jeep empty and refill it with straight aviation 100 low lead and run it for a few minutes then store it. Be sure to thin the 100 low lead with regular auto gas when you pull the jeep out of storage.

Custer · Post by **Custer** » Wed Mar 23, 2011 6:00 pm

Thanks, looks like I'm going for the mechanical pump.

Custer · Post by **Custer** » Wed Mar 23, 2011 6:03 pm

Also is there any way of testing my current mechanical pump short of trying to run the engine.
Thanks

Post by **wesk** » Wed Mar 23, 2011 8:12 pm

You would have to simulate about 1000 RPM which would be pumping the lever 500 times per minute.