Mysterious fuel leak around tank... - Ford Mustang Forum
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post #1 of 14 (permalink) Old 05-05-2019 Thread Starter
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Mysterious fuel leak around tank...

I have an 05' GT with just over 20K miles. Last weekend I backed out of the garage and noticed fuel smell and saw wet concrete. There was no fuel smell in the garage prior to starting the car. I looked under the car (with it idling) and fuel was very fast dripping off of the bottom of the fuel tank cover. Needless to say I pulled back in the garage and shut the car off. The fuel continued to drip for a while with the engine off, then stopped.

My guess is that the fitting from the fuel line to the fuel tank sending unit may have dry rotted or a fitting has become loose. This is a garage kept, weekend driven, never in the rain car. No rust anywhere on the car and there are no signs of mice in my garage at all so I doubt it's rodent damage.

I removed the lower backseat cushion and popped off the cover over the sending unit and nothing was there, no sign of any leak nor any cracks. I also smelled it, no smell around the sending unit opening. No sticky residue from dried gas. I turned the key to activate the fuel pump...nothing, no leak at the 90 degree fitting or where it goes into the tank. I didn't start the car, just pressurized the fuel system.

I also checked the fuel filler hose from top to bottom, no leaks.

You can see in the one picture of the fuel tank that fuel has run down the side from the top. However, there's no visible sign of a leak at the top of the tank.

The only thing I can think of is that some part of the fuel line has a leak between the 90 degree fitting at the sending unit on top of the tank where I can't see it. I'm assuming a 2005 car would have fuel lines that are compatible with ethanol mix fuels...right? That's the only thing that comes to mind is that possibly the ethanol mixed fuel has deteriorated the hose over time so there's a leak in it.

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post #2 of 14 (permalink) Old 05-06-2019
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The car is 14 years old, and could possibly benefit from new gas line hoses near the tank.



The hose in photo #5 looks like it's missing a hose clamp. Did you remove it to get a good photo of the hose?

If not, replace the clamp to see if the leak stops.



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post #3 of 14 (permalink) Old 05-06-2019 Thread Starter
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Thanks for the reply. It's hard to see but the clamp is there, it's never been removed and there's no sign of any leak there. The leak is originating above the tank. Looks like a fun weekend project of replacing the fuel line is in my future.
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post #4 of 14 (permalink) Old 05-06-2019
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Since you only have a leak when the car is running (and for a short time after key off), you have a leak in the line from the pressure line from the tank. The plastic lines will often rub on a brace/bracket and develop a leak under pump pressure. You'll probably have to lower the tank to be able to see where it's leaking/rubbing.
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post #5 of 14 (permalink) Old 05-06-2019
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if your dropping the tank, you'll need a special torq bit (tp-50). normal torq bits are square end star, the tp-50 has round end star. not sure why Ford has to use off the wall stuff but whatever. a standard t-50 will probably work but will be slightly loose and can strip out the bolt if not careful. good luck
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post #6 of 14 (permalink) Old 05-06-2019 Thread Starter
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Hey Travis, Here's the odd part, the leak is only on the driver's side of the tank, on the drive shaft tunnel side. If that makes sense.

I jacked the car up to look at it, the fuel appears to be coming from around the "hump" which has no penetrations or hoses near that area of the tank. As you know, the S197 fuel tank is two sided, it has a center hump that goes over up against the top of the driveshaft tunnel that connects the two about equal "cells" on each side. Per the diagrams that I can find the only hose that comes out of the tank is on the driver's side and runs down the front of the tank then heads to the engine. No fuel runs down the front of the tank near that fuel line.

I've taken off the two access covers under the back seat and there's no fuel at all leaking from the two caps to access the sending units, the 90 degree fitting, or the fuel line that comes out of the driver's side. The front of the tank on the driver's side is bone dry.

Nothing makes sense. If the tank had a hole in it, the fuel would drip out to a point below the hole then stop. If it's the fuel line and/or fitting that comes out of the tank on the driver's side, there would be evidence of the fuel running out, there's zero leaking there. Yet somehow when the car is running there's fuel running out of the tank.

My only option is to have the car hauled down to my mechanic and put it up on a lift. I will post an update after it's fixed.
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post #7 of 14 (permalink) Old 05-07-2019
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Could be the return line.
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post #8 of 14 (permalink) Old 05-07-2019 Thread Starter
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Mystery solved - ruptured line

After investing in an $85 video scope, the leak is a ruptured fuel line that runs on the front side of the tank before it turns and heads towards the engine. I have a picture of the split, but I can't post it on the thread.

The way the fuel was spraying out of the line, it appeared to be coming from an area of the tank where there was no fuel line. Mystery solved.

The rupture isn't from rodent damage, there are no chew marks, just the split in the line. I'm not sure how a car that spends it's life in a garage and only has just over 20K miles on it has a fuel line failure...but I guess it happens.

Is there anyone that's replaced their S197 GT fuel lines? Seems like it will be very difficult without a lift. If there are any suggestions for replacement (upgraded) fuel lines online I'd appreciate it.
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post #9 of 14 (permalink) Old 05-07-2019
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if the car sat for a long time perhaps the lines dried out and became brittle and then the sudden pressure, perhaps combined with a sudden impact, managed it.
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Nothing last forever especially if you rarely use it. ^^^

Maybe with a set of ramps, a floorjack and a good friend, you might be able to tackle this.
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post #11 of 14 (permalink) Old 05-10-2019 Thread Starter
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Fake news...mystery not solved.

Question: How many think that the images I attached from my scope appear to be a hose with a slit in it and fibers sticking out of where the hose failed? That's what I thought I saw...and no, I hadn't been drinking.

This afternoon I was looking at the Ford "fuel tube" assembly part #5R3Z-9J27-9A diagram and realized there were no fuel lines or any other hoses in the location that I thought I saw a hose. (BTW, that part number is one assembly that Ford doesn't make any longer.) I also checked another part of the fuel system in rear, part #5R3Z-9E325-A (This part is still available.) So, I jacked the car back up to get completely under the car to see exactly what I was seeing in the scope. I found the object again with the scope, left the tip pointing at it, then crawled under the car...and it was a seam, where it's stamped together and those "fibers" are tiny metal shavings at the stamp location. It just was an optical illusion on the screen, or maybe I was hoping it was that easy to find and seeing what I wanted to see.

So after I realized that what I saw on the scope wasn't a hose, I started the car for less than a minute to get it to leak again. After shutting it off, I got under the car to watch. It took a minute or two but fuel did start dripping off the driver's side of the tank, towards the drive shaft tunnel. I had my scope with me and started looking all over. None of the fuel system hoses or fittings leaked, at all. I had the back seat out and both access covers off over the sending units...zero leaks around the openings or at the sending unit fitting on the driver's side. I followed the Ford part diagram where all the fuel hoses are to make sure, no leaks.

Based on what I could see under the car with the scope, fuel is coming from the driver's side of the tank, towards the section that goes over the drive shaft tunnel. The only thing that makes sense is that the tank has developed a hole in it on top, so it leaks when the sending units come on...which makes no sense.

I've talked to my mechanic, owns the shop I go to, he said it's not likely that a hose rotted. The car has ethanol safe hoses and it's not old enough nor has it been in the weather enough to rot hoses. Rodents could have gotten it, however where it's leaking from on the tank, there are no hoses or fuel line connections and I haven't seen one mark that would indicate something has been chewing on the hoses.

I can't wait to get the car towed down to the shop to see it on a lift. I know where this is going, he's going to have to drop the tank...which means removing half the back end of the car and most of the cash from my Mustang aftermarket parts fund. Oh well...

Once I get it fixed I will post an update and photos.
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I know it sounds crazy but hear me out, ive read this type of fuel leak on another forum im a member of. what likely happened is a rock just the right size got lodged between your gas tank and the body of the car. over time and heat cycles, the rock rubbed a small hole in the tank. then after the rock had shrank from constant rubbing and the hole in the tank got larger, the rock dislodged and is no longer there. as far as dropping the tank, make sure its almost empty (DUH, I know lol). should only have to unbolt the drive shaft and remove the over axle exhaust pipes. good luck

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post #13 of 14 (permalink) Old 05-18-2019 Thread Starter
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bl817 - I think you're right, some how there's a hole in the tank on the driver's side, up near the "hump" in the tank. I'm not able to get my car down to my mechanic until next weekend to find out what's up which I know will involve dropping the tank to figure it out.

It's just odd (and frustrating) the car only has 20K miles on it, has always been garage kept, it's maybe been driven on wet roads 2 or 3 times so a rusted tank from the outside makes no sense. I find it hard to believe that condensation on the inside of the tank would have rusted it out. There would have been rust in the fuel that would have clogged fuel filter or caused poor performance from contaminated fuel. I had the fuel filter replaced last year and there was zero indication of anything in the fuel tank or line. What a PITA. I will post an update and pictures of what he finds.
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post #14 of 14 (permalink) Old 06-15-2019 Thread Starter
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Leak found...

I finally had the car towed to my mechanic. This is where having a lift vs. a floor jack makes a big difference. Long story short, I could not have the car running while up on a floor jack to see where fuel was originating from. I was crawling under the car after it was done dripping to try and locate the source of the fuel.

My mechanic starts the car, lifts it up and we both walk under the tank and immediately see the issue. Back story...I had Air Lift Performance installed on my car in January at a shop that does high-end builds. I saw their work, the cars look very impressive to me so I assumed all work would be done at a high level. Well...you know the old saying when you assume something.

As you can see in the pictures, the guy that did the install decided to drill a hole in the seam weld of the fuel tank so he could put a zip tie through it to hold an airline.

Now is when you hear the music from the Price Is Right when you lose a game on the show...we all know that tune.

Who drills a hole in any part of a fuel tank? Well, this guy did and it made my tank leak.

It reminds me of a saying that Mark Twain once said: "The thing about Common Sense is that it's not very common."

Thankfully the tank doesn't need replaced. The hole was plugged with fuel tank epoxy. I only wish I had found it before I had it towed there, I could have saved myself $250 and fixed it myself.

At least there was no weird tank defect and I can drive the car again.
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