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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old April 25th, 2008, 13:31   #1
NadaGasser
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Join Date: Mar 2002
Location: Green Valley, AZ
Fuel Economy: 51 mpg
Default Leak at Fuel Filter After Filter Change

Help! My 1999.5 New Jetta was running fine on B20 here in the sunny, warm state of Arizona, and since we will be driving to Wisconsin on May 11, I decided that the fuel filter should be changed, since it has not been changed since I bought the car last Fall. There were no fuel leaks before the filter was changed. There is a mechanic at a Texaco station here in Green Valley who is knowledgeable about VW cars (owned 16 of them in the past) and has worked on diesels, so I had him perform the filter changout. The filter was a Meyle with 2 new thermostatic valve o-rings.

Two weeks later, I noticed a rather strong odor of unburned fuel from under the hood, and when I looked, the ridge on top of the filter was full of fuel; and there were air bubbles in the clear fuel line from the filter to the injection pump. The leak appeared to be coming from the filter connection with the fuel return line to the tank. I stopped the engine and wiped off the top of the filter until no more fresh fuel was present. I then double-clamped the leaking connection and restarted the engine. Fuel again proceeded from the leaking joint and filled up the ridge on top of the filter. When I shut the engine down, a slight whistling sound was heard coming from the top of the filter .... where exactly I do not know.

Can anyone offer some clues as to what has happened? I spoke with the mechanic and he said he changed the o-rings on the thermostatic valve. I know in reading about fuel filters that mishandled o-rings can leak, but this does not appear to be the problem. Is the thermostatic valve prone to cracking if not handled with great care? HELP, please!

Mike in Green Valley, AZ
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Old April 25th, 2008, 14:47   #2
Jetiwarrior
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Mike,
The fuel filter is a pretty simple install. If the fuel is leaking around the return line control valve then you have one of the following problems.
1. O-ring not installed correctly or damaged
2. Retaining clip is missing or not installed correctly
3. Plastic control valve has a crack in it
4. Fuel filter has a manufacturing defect where
the o-ring seals.

Hope this helps you out.
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Old April 25th, 2008, 21:06   #3
unjester
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Also note that you can replace the T-fitting at the top of the fuel filter by itself. Pretty inexpensive part. In my experience they all start leaking at some point and need replacement.
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Old April 26th, 2008, 08:04   #4
Souzafone
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Mike, I've got the same exact car as you. It doesn't really matter what happened you either need o-rings or a tee. I fished mine out of the botton of my toolbox recently and re-used it at my most recent filter change with no problems, which brings me to the point. My last filter was ordered from a dealer as I needed a boost hose at the same time, and they sold me one from a '98 NB, with no tee. I used it most of the winter with no problems, and some people prefer it to correct filter for other reasons. The only problem is you can't fill it before installation. Just trying to give you an alternate fix. Good luck.
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Old April 27th, 2008, 10:08   #5
elmo_want_beer
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I vote the fuel tee fitting -- mine leaked a little, then when I tried to pull it out of the filter to check how the o-rings were seated, the tee came apart into pieces!! Ordered a new one from tdiparts.com for around $30.
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Old April 28th, 2008, 08:19   #6
mrGutWrench
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__. If you're getting fuel leaks, then what you're seeing is fuel from somewhere that there's pressure. That means the "return side" and would include the tee and its O-rings. The "side" of the fuel filter that's between the tank, fuel lines and engine is under suction. They can develop leaks but what happens is that air is pulled into the system - you rarely see fuel leaking out of that side of the system (certainly, if there's a major leak where you can see puddles, it's not over there because it would be leaking so much air that your engine wouldn't stand a cat in hell's chance of running).

__. So I second the opinion that it's over somewhere near the tee. Could be a crack in the hose going to the tee, the connection of the tee to the hose, the tee and it's O-rings, or the line out of the tee back to the tank.

__. But it's pretty certain it's over on that side.
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Old May 1st, 2008, 18:00   #7
NadaGasser
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Default Problem Fixed! But Don't Know Exactly Why!

OK, everyone, thanks for the input. I ordered a new T-valve from tdiparts and installed it this afternoon. No leaks! Here's what I discovered though with the old valve:

1) does NOT appear to be cracked. I would presume that if cracking occurred, it would have been during removal from the old filter, NOT when pressed into place in the new filter. Why? The only really good way to grab the valve for removal is to lift it via the two "handles", e.g., the two fuel line barbs. That puts (what we engineering guys say is) "beam loading" into the barbs which they are not designed to handle, and an old, brittle T-valve can be cracked. Conversely, when a T-valve is inserted into a filter, this is done by pressing down on the center of the valve, and the design of the valve is clearly intended to handle this push load.

2) O-rings did NOT fit their ring grooves well. They were a sloppy fit. The circumferential fit seemed snug, but the ring heights were shorter than the ring groove heights. In other words, the o-rings could be moved up and down in their respective grooves. This would present a potential leak path. My auto service provider said he replaced the o-rings on the T-valve with the new o-rings provided by Meyle. (Note: The new T-valve came equipped with new o-rings already installed. The fit in the ring grooves was very good, not sloppy as with the Meyle o-rings on the old valve).

3) I was not able to determine if the Meyle rings were nicked at installation. My vision isn't what it used to be, and I did not have a magnifying glass to give them a good look.

Bottom line: If I had to do this again from the get-go, I would NOT have told my mechanic to replace the existing o-rings with the Meyle o-rings. The old filter was not leaking at any of the connections, yet it APPEARED to be leaking from one of the connections after the filter changeout.

Here's what I think (FWIW) was the true cause for this leak: Bad o-ring seal between T-valve and filter, letting fuel by the o-rings and traversing the leg of the T to the return line to tank. There, gravity took over, making it APPEAR as if the leak was coming from the connection between the hose and the T.
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Old May 1st, 2008, 19:19   #8
unjester
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Glad to hear you got it worked out. Save your old T in case your new one develops problems - maybe it is not cracked from the beam loading and it just needs O-rings that fit it better.
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Old May 1st, 2008, 20:31   #9
mrGutWrench
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Quote:
Originally Posted by Mike in Oshkosh, WI
(snip) 3) I was not able to determine if the Meyle rings were nicked at installation. My vision isn't what it used to be, and I did not have a magnifying glass to give them a good look. (snip)
__. Yeah, speaking of old eyes, I did a fuel filter for MzLauraLee on her waggin and had some leaks. When I pulled the Tee, it appeared as if the O-rings were folded or twisted. I'm pretty sure that they weren't *nicked* (i.e. I didn't see [note two sentences above] any cut-type damage) but they sure weren't sealing very well.

__. I diagnosed that one by pouring a little "mineral oil" from the drug store on the area around the Tee. It's heavy enough that it sealed up the air leak temporarily, indicating to me that that was where the leak was.

__. Just like yours, I did new O-rings from the stealer down the street and that fixed it. (I was also careful to lube the barrel of the Tee, the O-rings and the filter bore and I was also careful to push *straight* in.)
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