Changing Spark Plugs on a 2008 STI Hatchback
 

I changed the Spark Plugs on my 2008 STI Hatch at the wknd and just wanted to give some useful pointers and to say the job is a big fat pig to do lol

First off, I installed NGK Laser Iridium pre-gapped plugs, I believe they are gapped to 0.6mm. Part Number - SILFR6A6 Batch Number 8659. Subaru Part Number - 22401AA670. I believe the ...6 at the end of the part number represents the gap size as the un-gapped version part number is SILFR6A.

I followed the workshop manual that can be found online (just search on google for 2008 sti workshop manual, there is a few places to download the manual in .pdf format) and got cracking.

So, couple of pointers:

* Use a 1/4" socket set to do the job as I used a 3/8" and it was tight. The angles you have to do things call for a small socket set to make it easier. I'd think a 1/2" set is just impossible. I was surprised at how far the spark plugs are recessed into the engine.

* Get a variety of socketry - that rhymes lol - such as different length extension bars, a couple of universal joints (the swivel/angle/elbow thingy) and obviously a 1/4" 16mm Spark Plug Socket. Or even an adapter to attach a 3/8" or 1/2" Spark Plug Socket to a 1/4" ratchet. Basically the variety of options makes it easier to get at the spark plugs in weird and wonderful angles. The more options you have, the better.

* This is personal preference but you could remove the rubber seal inside the spark plug socket that grips the spark plug. Only reason is after tightening the new spark plug and pulling the socket off, there is a chance the rubber seal could remain gripped on the spark plug and only the socket comes off. Getting a pair of pliers in the hole to retrieve the rubber seal would be really difficult. Bear in mind the rubber seal may act as a cushion on the spark plug porcelain when tightening but if the socket is straight, not at an angle and not putting pressure on the spark plug then thats ok. Alternatively you could lubricate the inside of the rubber seal a tiny bit to stop it gripping the spark plug too much.

* Use a flashlight and small mirror to see into the spark plug holes and check there is no debris or obstructions before you push the new spark plug in. You cannot see into the holes yourself as its too tight so most of the work is done by feel. Thankfully the engine is cast in such a way that the spark plug recess/hole is wide at the mouth and then narrows to the spark plug threaded hole so you do not have to poke around trying to find the hole. (oh er!) You'll see what I mean.

* You may find it easier to tackle the job from underneath the car or under the bonnet, I raised the car and removed the under shield so I could use either. Each spark plug location is different with different obstacles in the way so its trial and error to find your preferred method of attack.

* Dont force anything! Everything should come out and go in with ease, the coil packs should slide over the spark plug easy (they are made of a flexible plastic/rubber) and provided the threads are ok, you should be able to hand tighten the new spark plugs into their holes by holding onto the extension bar until you cannot tighten any further, then use the ratchet/torque wrench to finish.

As per the workshop manual, these are the torque settings:

Spark Plug - 21nm
Coil Pack Bolt - 16nm

Lastly, make sure everything remains as clean as possible, you dont want any road dirt getting into the spark plug hole or into the coil pack electrical connectors.

It took me a fair few hours to complete the job but a big sigh of relief once its done. Unfortunately the design of the boxer engine and its relationship to the car chassis means space is very tight. The rear spark plugs (the ones nearer the gearbox) are more difficult than the front as the chassis narrows towards the rear so if youre like me, there could be some colourful language, funny face pulling and lots of finger fumbling! If you are fairly confident with a spanner then it is an easy enough job, just take your time.

Hope that helps! :)

(Sorry no pics, I didnt think of it at the time)