Fuel Line Material?

OneLapper · February 01, 2009, 12:46:24 PM

Here's the skinny:

I FINALLY got around to installing a fuel pressure gauge. All I could get was a "spike" of 5 psi, the entire time from idle to WOT it read zero. I then plumbed in a remote fuel jug by installing 3/8" barbed fittings and clear nylon chemically resistant tubing. With 5 gallons in a translucent racing style 6 gallon fuel jug and the lines in the bottom, it easily sucked up the fuel and purged out the air, at which point the fuel pressure gauge read 20 psi at idle and about 60 psi at WOT! I relocated the fuel jug to inside the bus, ran the line through the window and told my oldest daughter to watch the lines, and off we went to road test it!

1000% improvement. The bus would actually accelerate..... Until the fuel return line popped off. It then proceeded to pump 2 gallons per minute onto the highway till we gently coasted to a stop. After we topped off and reprimed, off we went. Mission Success!

THE QUESTION: The PO had already run a SS braided fuel line and bypassed the oem copper linefrom the fuel tank to the engine. Should I attempt to replace it with another fuel line or install the modern plastic 3/8 stuff? I have no idea where the hole in the current line is, but it didn't fix the PO's previous problem, so I want to take the time to fix it correctly!

Thanks for any input!

Mark

JohnEd · February 01, 2009, 02:29:05 PM

Mark,

Just a guess here, but I think it looks like the PO tried to solve the problem by running a new line. Ever see those brake bleeding pumps that put a vac on the brake bleed fitting? Hand pump vac and a gauge to tell if it is holding. Disconnect you rear most fitting and put a vac on the fuel line at the front end and see if it holds. No vac means there is a hole in the line and that is a straight forward fix. Got vac holding and you are still looking. Your tank isn't empty is it?

I have had fuel pickup tubes perforate near the top of the tank. Fixed it with a piece of brake tubing and silver soldered it in. You could also verify by drawing a vac at the rear most fitting and verify that the fuel coming out of the tank is bubble free.

Whatever fuel line you use, make sure that it is speced to handle BioD.

HTH,

John

OneLapper · February 01, 2009, 03:58:34 PM

There's no doubt that the PO's replacement line has a hole in it, and I can only assume that the original copper tubing also has a hole in it.

I'm going to have to take the time and test the original tubing and the replacement tubing. Now that I've taken a few minutes to trace the PO's replacement hose, it's a Rube Goldberg job at very best. Right now I'm trying to work on this thing in the driveway. We've had a foot or more of snow in the two weeks, as well as below average temps. It's 80 miles to my shop so I'll have to stop twice to fill up my 5 gallon jug.

I've never used the plastic fuel line, but I like the idea of compression fittings, if permissible with fuel line, to splice inline with the existing fuel supply hose or tube.

JackConrad · February 01, 2009, 04:30:36 PM

Quote from: OneLapper on February 01, 2009, 03:58:34 PM
I've never used the plastic fuel line, but I like the idea of compression fittings, if permissible with fuel line, to splice inline with the existing fuel supply hose or tube.

Not sure about any "codes", but since this is a suction line with no pressure, I don't see why compression fittings would not work as long as the line is approved for fuel. We did this a few years ago on a friends 4104 that had a air leak in the line from the tank to the engine compartment bulkhead. We were at an antique tractor show and had to use what was available. As far as I know he is still running with this repair.
We ran a length of DOT brake tubing and used compression fittings (we also used the inserts in the ends of the tubing to prevent the compression rings from collapsing the tubing. Jack

OneLapper · February 01, 2009, 06:16:31 PM

Jack, was the brake tubing you used nylon or copper? I'd like to use the nylon brake line but I can't find any reference that is fuel approved. I have a coil of it at work so I'll check with the manufacturer tomorrow. My dad is a plastics engineer so I'll pass it by him. I'm sure that I can find some rigid nylon fuel line as well. I'll have to check around for that.

JackConrad · February 02, 2009, 05:44:53 AM

Quote from: OneLapper on February 01, 2009, 06:16:31 PM
Jack, was the brake tubing you used nylon or copper? I'd like to use the nylon brake line but I can't find any reference that is fuel approved. I have a coil of it at work so I'll check with the manufacturer tomorrow. My dad is a plastics engineer so I'll pass it by him. I'm sure that I can find some rigid nylon fuel line as well. I'll have to check around for that.

What we used was black nylon DOT tubing. I do not know if it is approved, but it is what was available where we were (miles from the nearest parts place). It has worked for about 3 years now. Jack

VanTare · February 02, 2009, 06:08:21 AM

onelappper there is nylon line appproved for fuel available it has been in use for years check under the hood of your car or pickup metal line is almost a thing of the past

David

OneLapper · February 02, 2009, 06:49:52 PM

David, I'm just curious if other bus nuts have used the DOT air line tubing for fuel. I have about 50 feet of the air line at work. I didn't get a chance to call around for bulk nylon fuel tubing today.

On another note, David, I pm'd you last week, trying to pick your brain on some reefer unit engines that may use tiny turbos. I have a customer's Yanmar 3 cylinder 3TNE engine we are turbocharging.

Thanks

Mark

NJT5047 · February 02, 2009, 07:24:05 PM

DOT air lines are designed to be hydrocarbon proof. They are exposed to engine oil and don't fail. Some air brake systems are full of oil...and water. And the lines are exposed to gasoline and diesel fuel, and oil leakage in the front of trucks.
If you're still looking for your fuel line leak, you don't have to use vacuum, you could use a pressure regulator set at 15 or 20 lbs and pressurize the line. Any leaks should become quite obvious and audible. Get your daughter to listen with you. Youngsters hear so much more than adult males....

As you say, if the PO's line install is poor, it's time to replace it anyway.
Flexible plastic fuel line is common in marine applications. Boats are like airplanes...if it says 'marine'...it's too expensive.
Steel tubing (brake lines) makes nice fuel lines. My MCI has what appears to be 1/2" black iron pipe for chassis fuel line. It's a heavy duty item.
I would not run any sort of rubber (even covered with SS braid) from the fuel tank. DOT would work fine...but nothing that could collapse when a vacuum is placed on it. You may not have a leak...the line may be sucking shut. Or as already covered, the pickup may be leaking air, or the pickup filter may be full of crap.
HTH, JR

OneLapper · February 02, 2009, 07:44:28 PM

JR, thanks for the info. I think I'm going to use the DOT airline I have at the shop that's laying around. I bought 100 feet of the stuff that I used when I installed the air throttle, so there's plenty left over. I haven't had the chance to talk to my father about the nylon material but your point about the operating environment make sense.

Now I need a day without snow in the forcast to get this bus to my shop to get it ready to go to SC in three weeks!

Mark

NJT5047 · February 02, 2009, 08:19:26 PM

What is the size of the DOT air line that you have? I'd have assumed that an air throttle would use 1/4" line?
Not to throw cold water on your fuel line, but I'd guess that the fuel line should be about 1/2" or 12mm? At the very least 3/8"..?? How long is the supply fuel line run? What is the ID of the OEM fuel line? I'd recommend matching the OEM ID.
Be sure that he fuel line flow is sufficient. The line flows a lot more fuel than the engine actually uses. The bypass fuel flow keeps the injectors cooled.
Most of the fuel is returned to the fuel tank.
JR

OneLapper · February 02, 2009, 08:24:33 PM

The oem and the replacement hose are both 3/8. The air brake line I have is also 3/8, so it'll work. I was surprised out much fuel circulates through the lines. The three or four gallons of fuel in the jug was very warm after about 8 miles!

leroy · February 03, 2009, 06:20:45 AM

replaced my fuel line with 3/8 id dot plastic air line, that was about 8 years ago ,still fine. it is on 4104
leroy

Highway Yacht · February 03, 2009, 12:13:06 PM

Quote from: OneLapper on February 02, 2009, 08:24:33 PM
The oem and the replacement hose are both 3/8. The air brake line I have is also 3/8, so it'll work. I was surprised out much fuel circulates through the lines. The three or four gallons of fuel in the jug was very warm after about 8 miles!

One thing you need to remember is that the "Hose" is measured by inside diameter and you get the full flow of the 3/8" and "Tubing" is measured by outside diameter so you will not have the exact flow especially if it is a thicker walled tubing like .065. The thicker the wall on the tubing means the smaller inside diameter on your tubing. Good Luck...

OneLapper · February 03, 2009, 06:38:56 PM

Quote from: jlink on February 03, 2009, 12:13:06 PM
Quote from: OneLapper on February 02, 2009, 08:24:33 PM
The oem and the replacement hose are both 3/8. The air brake line I have is also 3/8, so it'll work. I was surprised out much fuel circulates through the lines. The three or four gallons of fuel in the jug was very warm after about 8 miles!

One thing you need to remember is that the "Hose" is measured by inside diameter and you get the full flow of the 3/8" and "Tubing" is measured by outside diameter so you will not have the exact flow especially if it is a thicker walled tubing like .065. The thicker the wall on the tubing means the smaller inside diameter on your tubing. Good Luck...

Ah, good point. I'll have to look at this whole thing again!

Thanks

Fuel Line Material?

VanTare