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Skid plate/metal engine belly shield installation mk4 dieselgeek
Metal skid plate / engine belly shield installation
This article shows a comparison of skid plates and shows how to install one on a VW Jetta TDI, other cars similar.
The aluminum oil pan on the mk4 TDI is low to the ground and can be damaged by road hazards. Unlike most cars, it hangs below the front car subframe and is exposed under the car. Road debris like tire treads (they are made with steel cords) or roadkill may hit the oil pan instead of being somewhat blocked by the subframe. Because the oil pan is aluminum, if the car bottoms out in a pothole or hits road debris and cracks the oil pan, the engine oil will leak out. If the crack is big enough for oil pressure to be lost, the engine will quickly be damaged. Replacing the plastic lower engine cover (splash shield) with a metal skid plate will help protect it.
The stock plastic splash shield protects against dirt, small pebbles, and water only. This is important because it protects the drive belts at the front of the engine and keeps road salt/some dirt out of the engine bay. It also dampens sound, reduces wind noise, and improves aerodynamics. However it offers no protection against speed bumps, potholes, or road debris. If it's damaged you could find a used one but if it gets torn off then it means you were very close to oil pan damage. A metal skid plate usually costs less than a new stock splash shield and provides some protection. It also helps stiffen the chassis which can help handling. You could also install a steel bottomed oil pan or refresh the suspension to raise the ride height slightly. If you need new tires soon, taller sidewall tires will raise the car but make handling slightly softer. See 1000q: tire calculator to see how much tires could affect ride height.
This article shows installation of a dieselgeek skid plate on a mk4 Jetta. Any tips here are superceded by the manufacturer instructions and apply only to my car and this exact model of skid plate. A few metal skid plate options are listed below. I found the product and phone service from dieselgeek to be good enough to recommended but this page is not an endorsement or recommendation of any specific skid plate. A basic comparison of the various skidplates is listed below.
The hazard is caused by a few reasons. As mentioned above, the oil pan is exposed and hangs below the subframe. The TDI engine is heavier than a gasoline engine - this extra weight causes the front of the car to sit lower. While the springs are stiffer vs. a gas engine to account for this, age and mileage wears compresses springs and lowers ride height. The struts are tuned soft so when you hit a pothole or run over a speed bump, the front end can move more, potentially striking the ground. New springs and bushings will raise ride height in the front to new specs. Firmer struts will also help dampen movement and reduce bouncing of the car. This reduces how fast the oil pan could bottom out and also improves handling.
The articles on this site avoid scaremonger language and try to keep editorial to a minimum, so here's a story by "alovelyman" that made me laugh: "I pulled into a gas station which is used heavily by semi trucks. The entrance to this station has two small impressions where the semi tires have compressed the roadway creating a little bump in the road....Exiting my car I saw that some fool had left oil all over the parking lot. It took me a few seconds but once I saw it lead right to me I began the finest foul mouthed rant I've had in years." Total cost for tow and repair: $1700. A skid plate is not required but it's a cheap investment and provides a lot of confidence.
Note - a metal skid plate should not interfere with crash safety. In the event of a severe frontal crash, the engine mounts will break away and the engine should move under the car. The few bolts and anchors that hold the skidplate aren't going to stop the heavy engine/transmission from moving where it wants to go. I doubt that aluminum skidplates can withstand that amount of force and VW's OEM skidplate is steel (stronger than aluminum) and is mounted at the same points.
Parts and skid plate comparison
(click links to compare current pricing, all skid plates come with all installation hardware)
Optional: steel bottomed oil pan VW# 1jm 198 601t from metalmanparts
A few of the available skid plates are OEM VW steel, Dieselgeek's aluminum panzer, Defender-tech's galvanized steel, and Evolution's aluminum atlas. These part numbers are for reference only, double check with your vendor before ordering! If you have a New Beetle, I suggest an aftermarket piece because the OEM skidplate for the New Beetle is expensive (VW# 1c0 018 930a).
Dieselgeek's MK4 aluminum Panzer skidplate (the Jetta/Golf/New Beetle skidplate is pictured below) uses two steel front posts and a bent tab at the rear to secure the skid plate. The steel front posts are a direct copy of the OEM posts (steel tubes angled forward with a two-bolt welded flange). 10mm bolts hold the skidplate to the two front mounting posts and three 10mm bolts secure the plate to the rear subframe mounting points I added some spray on liquid soundproofing to make it stealth and add sound dampening (optional). Installation instructions at dieselgeek.com.
Here is clearance between the oil pan and dieselgeek skid plate.
The OEM steel VW skidplate is 1/3 heavier than aluminum and uses 2 thick front posts (2 bolts each). The disadvantage is that it's heavier and reduces ground clearance vs. the dieselgeek skidplate. In other words, it sits slightly lower to the ground than the other skid plates. It's also slightly harder to remove than the aftermarket skid plates because of the support arms on the sides. The advantage is that it's steel and its ribbed steel construction will hold up to heavy duty use. Then again, if your skidplate sees such heavy duty use that you can't use an aluminum skidplate then you should be driving another vehicle with more ground clearance. Pictured below is an OEM steel skidplate from a R32 golf.
OEM parts list for Jetta/Golf:
skid plate kit without sound deadener or side panels 1j0 018 930 b
VW metal skid plate for diesel VW# 1j0 018 930 b , skid plate for gasoline VW# 1j0 018 930 [c or h, depending on VIN]
front posts (quantity 2) VW# 1j0 018 885 a
rivnut (rivetted cap nut,quantity 7) VW# n 908 106 01
bolt (quantity 5) VW #n 100 704 03
stop buffer (quantity 3) VW# 1j0 018 977 a
retainer (quantity 3) VW# 1j0 018 967 a
sound deadener mat VW# 1j0 018 997
clip (quantity 9) VW#n 905 333 01
bolt (quantity 2) VW# n 908 704 01
The Evolution's aluminum Atlas skidplate uses 2 thinner front posts (1 bolt each) and a wide thick slot in the rear to hold the skid plate. It fits Jetta/Golf/New Beetle. Installation instructions.
Defender-tech galvanized steel skidplate uses 2 thinner front posts (1 bolt each) and a wide thick slot in the rear to hold the skid plate. 5 bolts hold the skidplate to the car. Because it's steel, it weighs about 10 lbs more than the aluminum skidplates. Installation instructions.
JS Performance's aluminum Armadillo has 5 bolts and a wide thick slot in the rear to hold the skid plate. It has the largest oil drain hole which could be either good and bad.
Raise the front of the car securely. Rest the car on jack stands, chock the rear wheels, and make sure the front of the car is safe and stable before getting underneath. See the TOS Agreement for the full legal disclaimer. Again, these exact tips are for the dieselgeek skid plate only.
Remove the plastic lower engine cover and side shields (t-25 torx screws and speed washers) Wash the underside of the car - you'll be doing some work underneath the car and it's nice to not be showered with dirt and rust. Always wear eye protection.
Note - this installation method was of a 2009 model and earlier dieselgeek skid plate which is also applicable to other models. For 2010 dieselgeek changed the installation of rivnuts which is explained in the video below:
Grease the inside threads of each rivnut thoroughly and set aside. You may also see it called a rivinut, rivenut, rivetnut, or rivet nut. The purpose of greasing them is to let the bolt threads slide and mushroom the rivnut as you tighten each bolt. If you don't grease it the threads could strip so apply plenty of grease to the bolt's threads! Mushrooming inside the frame is how the rivnut holds the car. When you install each rivnut, grease a bolt and washer, put them on one side of the install tool and hand tighten the bolt into the rivnut. Avoid getting grease on the outside of the rivnut as it installs easier with more friction against the body. Make sure to securely press the rivnut (or install tool) against the car so that it installs flat.
Here's a video showing more on rivnut installation on a mk4.
If the rivnut gets stripped, use a grinder to cut an "X" or star in the rivnut head and then chisel the head away. You can then punch the rivnut body into the subframe. You could also drill out the center and then punch the rest out. A third option is to tap new threads. If you need more rivnuts the part numbers are listed above.
Install 3 rivnuts in the front subframe at the circled holes below. These will hold the rear of the skidplate. Use the installation tool to hold the rivnut while you tighten it's bolt to 35 ft-lbs. Remove the bolt and wipe clean.
Circled below are the 3 rear rivnuts after installation.
Install 2 rivnuts for the front posts in each frame rail. The install tool has a cutout hole to go through the stud sticking out of the frame rail.
If you don't have an install tool, use the front post as an install tool to hold the rivnuts. You can now install the front posts. Each post should slant towards the front of the car. Repeat for the other side. Leave the 2 front post bolts loose during initial skid plate installation for proper alignment of all the bolt holes.
Cut the plastic sideshields to clear the front posts. They will be inboard of the front posts. Even if they are damaged, they can still be used since they are not structural to the skidplate at all. Refer to the manufacturer's instructions for exact dimensions. While they were off, I applied liquid soundproofing to them to help quiet the engine. See 1000q: soundproofing for more tips.
Attach the plastic sideshields before attaching the skid plate. Lubricate each front post's threaded hole with WD-40 and test thread a bolt to throughly lubricate the threads. Now lift the skid plate and attach 2-3 bolts to hold the skidplate from falling down. Put a washer above the center rear hole. Loosely hand thread the 5x 17mm bolts, make sure everything is aligned, and then tighten them all to 35 ft-lbs. I prefer to tighten the driver's side rear bolt first since it's at a slight angle. This should help prevent stripping of the rivnut. The skid plate will slightly distort while you tighten the other bolts. To minimize this angle and distortion, I placed a rubber washer between the skid plate at the driver's side rear bolt. Remember to tighten the front post bolts now that the skid plate is aligned.
The sideshields will only use 1 speed washer and 2 torx screws. The front screw may be too short so just use the long phillips screw to hold the front.