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The splash shield reduces noise, makes the car more aerodynamic, reduces front end lift at high speeds, and ducts cooling air underneath the engine. The most important reason to keep the splash shield intact is because it keeps dirt and water/road salts off the front belts, pulleys, AC compressor, wiring, and other stuff in the engine bay. However, the splash shield is not a skid plate and will not protect the aluminum oil pan against hitting road debris or if the car bottoms out in a pot hole. It protects against dirt and water only. If you want impact protection for the aluminum oil pan get a metal skid plate. If your car is lowered, a metal skid plate becomes more important. See dieselgeek.com for the VW Passat TDI skid plate.
All Passat splash shields (1.8T, V6, W8, TDI) are interchangeable between models and B5 vs. B5.5 (the early body style vs. later body style). The W8 has 2 more air ducts at the front. The TDI has a rear splash shield in addition to the front one so it needs different fasteners where they meet. All use the same plastic side fasteners. The splash shield will also fit on the same generation Audi A4 or Audi A6.
The silver fasteners are 18mm long. The black are about 20mm long. The brown (TDI only) are 21.5mm long.
Front of splash shield: There are normally no rubber washers in the front so use 2 black on sides/1 silver in middle -plus the 10mm nut in the center. If you want to add rubber washers use 2 brown on the sides, 1 black in the middle, plus the 10mm nut.
Gasser rear of shield: 3 silver (should have rubber washers to hold
them in place when the shield is off)
TDI rear of the front shield/front of the aft shield: 3 brown when using rubber washers, 3 black when not using rubber washers
TDI rear of the aft shield: 2 silver
-VW Passat TDI metal skid plate from dieselgeek.com
4 cylinder splash shield: 8d0 863 821 s
TDI front splash shield: 3b0 825 235 b
TDI rear splash shield: 4b0 863 822 g ,(or 4b0 863 822)
6 cylinder splash shield: 8d0 863 821 q
w8 splash shield: 3b7 825 235 a
NOTE: ECS tuning used to sell cheap splash shields w/no sound insulation for cheap, they have since increased the price. Any genertic one will work because it's just a piece of plastic.
brown 21.5mm fasteners: 3b0 805 121
rubber washer: 4a0 805 137
plastic side screw: 4a0 805 121 a
plastic side snap/clip: 4a0 805 163
You don't even need to raise the car to remove the splash shield, just reach underneath with a stubby screwdriver.
The rear of the front shield should have rubber washers to sandwich the fasteners. This holds them in place when the shield is removed. You can use them on the front too but you may need longer fasteners to account for the extra length. If the fasteners are too loose they will fall out. The purpose of the rubber washers to make it more snug. Don't move the silver ones to the front sides because they're too short and the splash shield will fall out - it won't be secure.
The special fasteners are called Dzus lock fasteners. After you think it's tightened all the way, turn them counterclockwise a tiny bit to feel that they're locked in place and then back tight all the way. There's a little hump in the thread where it can trick you into thinking it's locked.
If you're short Dzus fasteners and you have to drive, the 2 front side and 10mm nut in the center take priority since the wind can catch the splash shield at highway speeds and pull it down. Use plastic zip ties for the rest. Replace them as soon as possible since the splash shield can become damaged.
If you have a TDI, the front of the rear shield goes under the rear of the front shield. This prevents the wind from catching it and it'll only fit one way anyways. If you have another model I believe the rear shield will also fit yours but due to the cost I wouldn't buy one.
ECStuning used to sell replacement shields for cheap with no sound
insulation. The sound insulation is the main difference between
models. The W8 shield also has 2 extra air ducts at the front. If
you are missing a splash shield or have a damaged one this is a good
option. To transfer the sound insulation to a new shield, thoroughly clean
any grease or oil off both surfaces and use contact cement to glue it
Because I had a new shield I put some extra soundproofing mat (the silver
stuff) and a few rivets at the leading edge of the sound insulation in case the
wind lifts it up.
Here is the rear shield on the Passat TDI. After 10,000 miles, the
intercooler leaked some oil from the couplers which dripped down onto the mat.
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