Fuel Bleeding a HEMTT

[bsteinborn]

Replaced the fuel filter today on the HEMTT, now I need to bleed the air out. TM 9-2320-279-20-1, Section 2-18 discusses bleeding the air at the fuel filter housing with a priming pump. Is the TM talking about a hand primer pump similar to the one at the link below? I guess the pump is a plunger that is compressed a few times? How do you know if the system is primed? Thanks.


https://www.amazon.com/Bosch-2447010038-Hand-Primer-Pump/dp/B001CO92F2

 

[Tornadogt]

I removed the fuel return line at the fuel tank, then pressurized the fuel tank until fuel comes out of the fuel return line. Reconnect the fuel return line and start the truck.

 

[DrillerSurplus]

I removed the fuel return line at the fuel tank, then pressurized the fuel tank until fuel comes out of the fuel return line. Reconnect the fuel return line and start the truck.

It's a great way to get the fuel all the way through the system, but a warning if you haven't done this before- use very low air pressure- like maybe 2 or 3 psi, 5 psi tops!
The fuel tanks aren't designed for pressure and it is easy to split it open. 2 psi will lift diesel a little more than 5 feet vertically which should be enough.

 

[Coffey1]

I used way more than that on 5 tons tanks.
5psi won't do crap in a 155 gal hemtt.
You might as well open lid and burp in it lol.

 

[DrillerSurplus]

I used way more than that on 5 tons tanks.
5psi won't do crap in a 155 gal hemtt.
You might as well open lid and burp in it lol.

Military vehicles' fuel tanks are generally stouter than those in commercial vehicles. If you have experience, you can make your own decisions, I wanted to warn those with less experience.

How much pressure it takes to do damage depends on the shape and construction of the tank. The cylinder shape of the HEMTT fuel tank can take more pressure than a rectangular tank, the ends would bulge out and warn you without splitting anything. A rectangular tank like the one on the MK48 is riskier. Let's say the tank on the MK48 is 18" wide and 48" long which is more than 800 square inches, then 5 psi is putting more than 4,000 pounds against the top of the tank.

If you measured the water pressure at 10 feet deep in a swimming pool it would be the same as 10 feet deep in Lake Superior or a garden hose up in the air 10 feet. The size of the tank does not matter.
5 psi will lift diesel fuel over 12 feet in a 3/8" fuel line or a 36 inch diameter pipe. The fuel filters won't create any back pressure at the very low flow rate bleeding the lines unless they are totally plugged up.

There is lots of literature out there that recommends not exceeding 3 psi test pressure unless the tank is built for pressure.
Here is a link to Coast Guard regulations on fuel tank testing: http://www.uscgboating.org/regulations/assets/builders-handbook/FUELSYSTEM1.pdf
There are some diagrams pages 7-9 and the test procedure starts on page 89.

I built a at least a hundred flat tanks to haul water in the drilling business, lots of them about 4'x8'x3' tall and a bunch of flatbeds 8' wide x 22 ' long that held 2,000+ gallons of water. The crews split a few of them by inadvertently blocking the vent so they pressurized the tank when it got full- takes about 5 seconds to turn the tank into a giant pillow then it splits a seam. I might have a few pictures still.

Anyway- the thing is I really like the efficiency of pressurizing the tank to bleed the system, but I want folks to know they can't drill and tap a quick connect into a cap for their fuel tank and hook the shop air up to it.

 

[Floridianson]

You need a primer pump like the 809 series has an two hoses for fast and easy priming is what I found. A clean jug of fuel and the fitting that screws into the filter block. That is the way I have always done Detroit's.
Works on Cat's to. By the time you do the air/fuel tank thing I would be down the road. You can also leave the hand pump installed.

 

[73m819]

I have used a cheap air pressure regulator and gauge with quick disconnect on the in/out, hook up my air sources, set to 3 to 5 lb then to the fuel tank, very cheap, very safe, very easy. When adding air to a tank or fuel system, or in fact any closed system, add it SLOW to ALLOW things to ADJUST to the pressure. I have seen people nearly killed by OVER pressurizing or pressurizing WRONG.

REMEMBER, it does not take a lot of air pressure to KILL YOU.

 

[wreckerman893]

Many of the HEMMT's I encountered had an air valve installed in the fuel cap. This was used to put LOW pressure on the fuel system.

Detroits are notoriously hard to prime. Even on civilian trucks it was a bear to get them to fire if they had lost prime.

That's one reason you never, ever want to run one out of fuel.

 

[DrillerSurplus]

Many of the HEMMT's I encountered had an air valve installed in the fuel cap. This was used to put LOW pressure on the fuel system.

Detroits are notoriously hard to prime. Even on civilian trucks it was a bear to get them to fire if they had lost prime.

That's one reason you never, ever want to run one out of fuel.

I've seen some of those Schrader valves on fuel caps. Along with my own experiences, that's what made me make the original warning post. If someone didn't know they could easily assume it was OK to hook the air up without paying attention to the pressure. We ran a lot of the Detroit 6V92 up until a couple of years ago and usually used the air pressure in the fuel tank method to prime the system.

Floridason's idea is great. I have a little 12 volt electric fuel pump with some 3/8ths fuel line in my tool kit that I use for lots of different purposes, including priming fuel systems.

 

[Floridianson]

Buy the right tool. What if you need to change the fuel filter and no air around. Buy the right tool.

 

[Coffey1]

If the truck is aired up at the time you change it you have air.

 

[JDToumanian]

I've never had any trouble priming, but I'm also careful to avoid getting air in the system. The procedure for replacing HEMTT fuel filters, if I recall, is to remove the old filters, fill the new ones with fuel, and install them... No bleeding necessary, the engine is capable of passing that amount of air without stalling. But if it's lost prime, I made up the pump kit shown in the pic below, same pump as posted earlier. They're available on eBay and elsewhere for around $50. They're designed to mount in the dash or control panel and be plumbed in permanently, but they're also great as a stand-alone pump with some hose barb fittings and hose. Unscrew the pipe plug on top of the final filter housing and install a barb fitting, connect the pump with the output hose going into a coffee can or whatever, and pump until there's no more air bubbles.

Jon

 

[Ford Mechanic]

Let's see pics of your install!

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[Floridianson]

Think I would install it close to the fuel filter block. Leave the out end hooked to the filter block and the suction line long enough to fit in a gallon jug. Have some kind of cap made up to keep dirt out of the open end. Mine is just sitting in the engine bay of the crane but before I just kept it in the tool box so I could service other motors.
Also I would like to see a TM where it calls to fill the uninstalled filter before install.

 

[JDToumanian]

Also I would like to see a TM where it calls to fill the uninstalled filter before install.

It's in TM 9-2320-279-20-1

Section 4-9 For the Fuel-Water Separator:

1 - Open drain valve and drain fuel-water separator.
2 - Remove T-handle, preformed packing, lid, and preformed packing.
3 - Remove filter element.
4 - Install filter element.
5 - Close drain valve.
6 - Pour clean diesel fuel into body of fuel-water separator until full.
7 - Wet lid and preformed packing with fuel.
8 - Install preformed packing, lid, preformed packing, and T-handle.

Section 4-11 For the Secondary Fuel Filter:

a. Removal.
NOTE - Secondary fuel filter is a spin-on type.
1 - Remove filter element and gasket from housing.
NOTE - Remove housing only if replacement is necessary.
2 - Remove fuel line and elbow from housing.
3 - Remove fuel line and bushing from housing.
4 - Remove fuel line and elbow from housing.
5 - Remove plug, two screws, lockwashers, washers, and housing.

b. Installation.
NOTE - Follow steps (1) through (5) only if new housing is to be installed.
1 - Install housing with two screws, lockwashers, and washers.
2 - Install plug.
3 - Install elbow and connect fuel line.
4 - Install bushing and connect fuel line.
5 - Install elbow and connect fuel line.
6 - Fill filter element with fuel.
7 - Moisten gasket with fuel.
8 - Install filter element and gasket on housing. Hand tighten filter element.

Jon

 

[Floridianson]

I would never believed it. I will always prime my systems with the filter installed empty no matter what a TM says. Don't know why DD or the older Cat's did not have a primer pump in the engine bay. I still stand by my right tool for any job. Tanks

 

[JDToumanian]

I would never believed it. I will always prime my systems with the filter installed empty no matter what a TM says. Don't know why DD or the older Cat's did not have a primer pump in the engine bay. I still stand by my right tool for any job. Tanks

I agree completely about having a primer pump in the tool box, also that engines without an electric in-tank pump should have had a hand primer pump as standard equipment. The pump is better and (in my opinion) easier than pressurizing the fuel tank. Filling the filters with fuel just saves even more time compared to attaching the pump on engines not equipped, though I'd definitely still have a pump around, because when the engine passes the little bit of air that remains in the filters after filling it usually sputters a bit... Though I've never had one stall.

 

[DrillerSurplus]

I would never believed it. I will always prime my systems with the filter installed empty no matter what a TM says. Don't know why DD or the older Cat's did not have a primer pump in the engine bay. I still stand by my right tool for any job. Tanks

I agree with the right tool for the job.
Leaving aside how to get the fuel moving to prime, I'm curious why you prefer to install the filters empty? It does seem like it would be cleaner, it's hard not to slop at least a little fuel out when you go to install a filter that is full of fuel.
The engines on the drilling equipment (trucks or stationary) I worked on were usually pretty high horsepower with big primary & secondary fuel filters that would take a while to fill with the small primer pump most of them had, so I always filled the filters unless they were installed in a place that would slop a bunch out as the new filter was installed. If it was a routine filter change the engine would almost always start right up without needing to bleed at all.

 

[Ford Mechanic]

I agree with the right tool for the job.
Leaving aside how to get the fuel moving to prime, I'm curious why you prefer to install the filters empty? It does seem like it would be cleaner, it's hard not to slop at least a little fuel out when you go to install a filter that is full of fuel.
The engines on the drilling equipment (trucks or stationary) I worked on were usually pretty high horsepower with big primary & secondary fuel filters that would take a while to fill with the small primer pump most of them had, so I always filled the filters unless they were installed in a place that would slop a bunch out as the new filter was installed. If it was a routine filter change the engine would almost always start right up without needing to bleed at all.

Cause the fuel you filed it with will be unfiltered going straight to the IP

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[Coffey1]

What! Ford it would be filtered once in cansiter it has to pull it through filter