You may see online instructions for gasoline Passat which mention a filter tucked next to the gas tank - your TDI has no filter there.
The fuel filter clamp is a 8mm triple square (not torx) bolt and the bolt head is (of course!) facing the back of the engine. I replaced mine with a regular hex head bolt so that it can be loosened with a ratcheting head wrench and is easier to access. You only touch it once every 20,000 miles so bolt replacement is optional.
Change the fuel filter every 20,000 miles or as needed. All fuel filters linked here are made by Mann or Meyle so don't worry about buying a "non genuine" VW part.
If you are using high percentages of biodiesel like B85 or B100, change the filter early since biodiesel will clean out the old buildup and clog the fuel filter if there was significant build up in the fuel system. As a safe interval, 1000 miles and then again at 5000 miles, your mileage may vary with biodiesel. A more economical idea is to install a small clear inline fuel filter before the main fuel filter to filter out larger particles and let you see how clogged the fuel filter may be.
Early symptoms of a clogged fuel filter are stumbling at high rpms or lack of power. A general lack of power could also be limp mode, see 1000q: TDI limp mode and 1000q: TDI constant low power can't rev for causes and possible solutions. Make sure that these symptoms are not caused by an air leak in the fuel line or a clogged pickup at the fuel tank. Bacterial or algal growth in the fuel tank can clog the pickup. It's also possible that the low pressure in tank electric fuel pump, the lift pump, is failing or bad. This can cause hard starting or a stalled engine due to fuel starvation.
Safety disclaimer - you are working with open fuel lines and fuel vapors
when you change the fuel filter! Make sure that there are no sources of
ignition, spark, or open flames near the car or where fuel vapors could reach.
Work only in a well ventilated area where any fuel vapors can be immediately
evacuated and if fuel is spilled, clean it up before you continue working.
Although diesel vapors are not as flammable as gasoline vapors (as seen in the
video below at the 1:00 minute mark - it's a demonstration only do not try
that yourself!), you still want to comply with all cautions in your factory
service manual. Wear eye protection at all times when working on your car.
See the TOS Agreement for the full legal disclaimer. Diesel fuel will melt
asphalt and rubber lines on your car so clean up any spills immediately.
Make sure to use gloves because diesel fuel has a strong odor and you don't want
it soaked into your hands.
There is a temperature sensitive recirculation valve on the return line. When below 59oF, the valve recirculates return line fuel to the filter and help regulate the fuel temperature. When the fuel is above 88oF, it should switch and recirculate fuel back to the fuel tank. The return line fuel is warmer than outside temperature because it's heated by the pressurization and compression from the injection pump and ambient heat from the engine and fuel lines. If this valve or any of the fuel lines are not sealed well, it will let air bubbles into the fuel lines and this could result in engine stumbling or a hard/no start condition. Make sure the o-rings and fuel line clamps are seated properly. The arrow on the recirculation control valve should point toward the fuel tank to the rear.
If you have a recirculation T and want to get rid of it (due to leaking or you live in a warm area), you can use a block off T, available from kermatdi. A block off T should increase power slightly by making sure you get cool fuel. I suggest leaving it alone if you live in a cold area or use biodiesel since some warmth is a good when cold. There are also better and more productive power increases available from other modifications, see 1000q: basic power mods for more details.
You may hear that the fuel filters are heated, this is true only in the sense that they are slightly warmed by the return line fuel. There is no active or electric heater unless someone installed an aftermarket heater for a veggie or grease system and you wouldn't want diesel or biodiesel to be too hot anyways.
Although you are supposed to drain water every 10,000 miles, I have never seen any water in my fuel. Water from condensation would be present in fuel that has sat for a long time or that has contamination from the gas station. The water drain drains the whole filter out the bottom when unscrewed.
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8mm triple square bit (not torx)
paper towels and vinyl/latex/nitrile gloves
1 fuel filter, either:
VW# 1j0 127 401 a (1j0127401a) or
VW# 3b0 201 148 (3b0201148)
optional parts if needed
VW# 1j0 198 247 (1j0198247) 2 o-rings (should come with filter)
VW# 1j0 127 250 (1j0127250) fuel-T spring clip (mickey mouse ears clip)
VW# 1j0 127 247 j (1j0127247j) fuel-T (comes with o-rings)
Here is a picture with the engine cover off to get
familiar with the area.
Remove the plastic engine cover (3x 10mm nuts).
Loosen the fuel filter clamp using the 8mm triple square bit (yellow arrow
below) I don't know why they used a triple square bit here so I replaced
it with a normal hex bolt that can be loosened with a ratcheting head wrench for
easy clearance. If you want more clearance
on the lines, pull them out of their plastic clamps (yellow box below).
Remove the spring hose clamps on the fuel filter hoses. Remove the fuel lines from the filter and wrap/clamp them. Diesel fuel eats rubber so wipe up any spills.
The filter can then slide up and out. Make sure to replace the
o-ring on the return line T.
Pour some fuel or fuel additive like power service or diesel purge into the
filter. Your engine has an electric fuel lift pump in the tank but filling
the filter with fuel will help.
Turn the key to on and leave it there for a second. Repeat. This runs the electric fuel pump in the fuel tank to prime the fuel system. Repeat a few times and the car should start without too much bucking. Below is a video showing the entire procedure.
An advanced way to prime the fuel lines is to attach a clean hose to the fuel filter outlet going to the engine (the one in the middle). The hose should empty into a clean jar. Turn the key to ON but not start. This will run the pump for about a second as long as the engine isn't running and is much more effective at purging the air out. Repeat until you see fuel in the jar and then empty the fuel into the fuel tank. You may have to cap the exposed line at the fuel filter or fuel will squirt out.
If the fuel rails in the cylinder head were run dry, you can also do this method on the return line coming back from the engine.
Here is what's inside the fuel filter housing, click to enlarge the thumbnails.
If you ever need to remove the bracket, remove the 3x 10mm bolts and 1x 10mm nut holding
it down (yellow arrows below).
You should be able to reach them with extensions or a wrench. Here you can see the original 8mm 12 point bolt that I replaced with a regular hex bolt.
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