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Old 08-03-2005, 09:10 AM
John Slade's Avatar
John Slade John Slade is offline
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Default Fuel hose leak

Here's a nasty failure mode to watch out for.

After fitting a new fuel pressure sensor I turned on the pump to check for leaks. The sensor fitting was good, but there was a slight smell of fuel which I traced to the regulator. There was a very slow drip which stopped after a few seconds. I stripped and rebuilt the regulator. Next pre-flight I pressurized the system and checked for leaks with a flashlight. The main return hose from the rail (steel braided teflon 1000PSI) was a little wet. I removed the cowl and turned on the pump. No leaks. I removed the hoses from the regulator and pressurized the entire rail & hoses to 100 PSI. The pressure held for more than 10 minutes. I put it all back together, re-installed the cowl and tried again. No leaks. I left it overnight, then did another check with the pump on. I had a steady drip from one hose that stopped after a few seconds. I ran the engine and did some taxiing, then checked again. No leaks.

Next day I did another preflight check with a flashlight. Again the hose was a little wet, but the leak went away after a few seconds and the hose dried out. After removing the cowl there were no signs of a leak. Last night I checked again. This time I had a jet of fuel from the middle of the return hose. I removed the braided teflon hose to find a dark spot at the point of the leak. The hose had not been rubbing on anything and was not abraded. The damage looks a lot like the result of an electrical arc, but there's nothing for it to short to anywhere near.

My theory is that this hose carried cranking amps at some time or other. I'd swear I've never cranked the engine with the ground strap off, but this is the only way I can imagine that this damage occurred.

Anyone have a better theory?

John (checking my other hoses)
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  #2  
Old 08-03-2005, 10:31 AM
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SSSsssssshhhhHHH !!!
John you are going to give one of these crazies the idea they can save weight by using steel braided hoses as engine grounds!
Hard to believe something like an Earl's hose would leak.
Glad you were persistant enough to catch it. These things can be elusive, passing off the smell of fuel or a drop of oil as a single time event will certainly not have a good ending. I had a large Perkins diesel in my sailboat and the fuel injection was at such high pressure it was impossible to see the leak. A mechanic said I would not be happy with the solution but it worked; you clean up everything in sight, degrease and dry, then blow talcum powder everywhere (the messy part), then run the engine. The leak was like a tiny laser beam, where it showed up was no where near where it originated.
...Chrissi
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Old 08-03-2005, 08:44 PM
Larry Wiechman Larry Wiechman is offline
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Quote:
Originally Posted by Cozy Girrrl
A mechanic said I would not be happy with the solution but it worked; you clean up everything in sight, degrease and dry, then blow talcum powder everywhere (the messy part), then run the engine. The leak was like a tiny laser beam, where it showed up was no where near where it originated.
...Chrissi
The powder method works great! Try painting the suspected area with a thin paste made of powder and alcohol. Dries fast and stays where applied.
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Old 08-03-2005, 09:00 PM
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Quote:
Originally Posted by Larry Wiechman
The powder method works great! Try painting the suspected area with a thin paste made of powder and alcohol. Dries fast and stays where applied.
Brilliant Larry!
Thanks, Chrissi
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Old 08-03-2005, 09:32 PM
Nathan Gifford Nathan Gifford is offline
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Quote:
Originally Posted by Larry Wiechman
The powder method works great! Try painting the suspected area with a thin paste made of powder and alcohol. Dries fast and stays where applied.
Would acetone work better? We use it at work to clean out analyzer cells.
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Last edited by Nathan Gifford : 08-04-2005 at 09:28 AM.
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Old 08-03-2005, 10:38 PM
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Quote:
Originally Posted by Nathan Gifford
Would acetone work better. We use it at work to clean out analyzer cells.
Please not anywhere around foam sandwich construction, it will dissolve the foam core.
...Chrissi
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Old 08-04-2005, 09:30 AM
Nathan Gifford Nathan Gifford is offline
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Quote:
Originally Posted by Cozy Girrrl
Please not anywhere around foam sandwich construction, it will dissolve the foam core. :eek:
...Chrissi
Glad to know that. Does it matter whether you use ethyl, methyl or isopropal alcohol. I know there are probably a bunch of people who would prefer ethyl...
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Old 08-04-2005, 01:47 PM
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John, Take a very close look at the discolored area, can you see if any of the braided wires that have gotten so hot that they melted and now have a little ball on the end?? If so, then it was an arc.

I ask this as its possible that the discolored area could possibly be just that, discolored from the leak, (car gas I assume) and there was no arc.

If it really is an arc, it looks like the arcing is localized. It appears as if this area of the hose touched a +12 wire or terminal. Is it possible this could have happened during assembly, i.e. one side of the hose was disconnected, and dangled and hit a starter connection (or something like this)???

I would think that if you attempted to draw a large current through the braiding on the hose (like with a starter), the heating, damage, and discoloration would be uniform through the entire length of the hose. Actually, I don't think that this would hurt the hose at all. The braiding looks good enough to handle a couple hundred amps.

Waiter
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Old 08-04-2005, 05:10 PM
DustinD DustinD is offline
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I think you are too optimistic about the amp carrying capacity of fine steel wire. Most electrical charts like the one I am linking to indicate a very low amperage capacity for copper wires of the same size. http://www.powerstream.com/Wire_Size.htm

Maybe the electrical load was spread out over most of the hose diameter for most of it's length, but had to concentrate at that one point on only a few wires to enter or exit the hose. That could explain why that small point heated up enough to discolor. I imagine there is only one entry and exit path on the cable, and since the ends are steel fittings that can handle a larger charge than a few small wires they probably would not heat up enough to damage or cook anything.
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Old 08-04-2005, 05:27 PM
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That car gas stuff is giving us serious cause for concern; we take a motorbike with us every year to osh (runs for ice in campground) and it ran the first day for a short while, then the next day would not keep running. Long storey short: all the fuel lines had turned to goo.
There is a clear line, a black line, a rubber breather in the gas cap, and a rubber stopper/grommet that the lines go into the top of the tank, everything was goo and when touched or pulled was like soft chewing gum and snapped off. Good thing there was a full line hardware store in town.
Sounds more and more risky to me.
...Chrissi
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Old 08-05-2005, 11:05 AM
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Quote:
there was a full line hardware store in town.
As in a full line of people needing the same stuff for the same reason?

Yes, the autogas game is a little worrying, isn't it. I've seen no problems so far but I've always refueled from the same local station (humping gas aint fun either). The mogas stations seem to be few and far between, and many of them seem to have 80 octane. Not too good for a turbo Maybe this is another good reason for having entirely seperate fuel systems. On long trips I might put mogas in one side and avgas in the other.

Speaking of motorbikes, I just picked up a Go-ped on ebay. These gas powered skateboards fold flat to about 30 inches long * 8 inches high, weight 20 lb, carry 400 lb and go 20 mph for 100 miles on a gallon of 2 stroke. If it works out I may get another one for Char (or for me, depending on how you look at it) .

Good to have the forum back. Thanks Dan
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