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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 November 18th, 2007, 12:04   #1
downcycle
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Join Date: Sep 2005
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TDI(s): '01 Golf
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Default Fuel line flow diagram

Can someone point me to or explain to me the flow direction of the four lines going into and coming out of the fuel filter? This is purely for my own understanding as I head into a fuel filter change. I have searched the forums to no avail. Thanks to anyone who can help.
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Old November 18th, 2007, 12:10   #2
downcycle
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I should say that this is my best guess as to the lines, there are 2(?) fuel lines coming from the tank, one of which goes into the filter, the other into the thermostat. The line into the filter is drawn by the clear line to the engine. The black line I'm not really sure about. I can't decide if it's going to, or coming from the pump, but the only reason I could think that it would be coming from the engine is if it was trying to increase flow by adding warm fuel? That's my best guess, so someone straighten me out. Thanks.
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Old November 18th, 2007, 13:02   #3
mrGutWrench
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Quote:
Originally Posted by downcycle
I should say that this is my best guess as to the lines, there are 2(?) fuel lines coming from the tank, one of which goes into the filter, the other into the thermostat. The line into the filter is drawn by the clear line to the engine. The black line I'm not really sure about. I can't decide if it's going to, or coming from the pump, but the only reason I could think that it would be coming from the engine is if it was trying to increase flow by adding warm fuel? That's my best guess, so someone straighten me out. Thanks.
1) From the tank to the filter -- it seems to come out of the inner fender, near where the hood closes;

2) From the filter to the fuel pump/engine (fuel pump in a "VE" engine -- '99.5 - '03 MY).

-- These following two attach to the "thermostatic 'T'" and return fuel from the engine to the tank --

3) From the fuel pump to the "T" on the filter;

4) From the T back to the tank -- this one runs parallel to (and is clipped to) #1, above at the inner fender.

__. If the fuel is warm, don't even think about the "T" -- in that case, fuel goes straight back from the engine to the tank like the T wasn't even there. So 3 and 4 act like a single fuel line.

__. It's a pretty simple "single loop". The only things tricky is that the filter in in the loop and the "T" is too. But it's pretty simple.
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Old November 30th, 2007, 08:10   #4
elmo_want_beer
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Just curious, how warm is the fuel that returns to the tank? I wonder if it is warm enough to significantly warm up the fuel in the tank... that way I could run a higher blend of biodiesel in the winter as long as I can keep the car warm overnight...
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Old November 30th, 2007, 08:36   #5
weedeater
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It's fairly warm. But if the car is cold, then it recirculates through the filter before going to the tank. In really cold weather (probably colder than what you would see), I don't think it keeps the tank that warm. Hence winterized fuel is still required.
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Old December 1st, 2007, 09:44   #6
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Quote:
Originally Posted by elmo_want_beer
Just curious, how warm is the fuel that returns to the tank? I wonder if it is warm enough to significantly warm up the fuel in the tank... that way I could run a higher blend of biodiesel in the winter as long as I can keep the car warm overnight...
If you contemplate doing this, please modify the fuel pickup. You'll appreciate this the first cold day.

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