Paul's Travel Pictures

Subaru Forester Spark Plugs Replacement Guide
How to check or change the FB25 2.5L boxer engine's spark plugs in a 4th generation 2014-2018 Subaru Forester.

Main Menu                 Home                Digital Cameras                Misc. Pictures                 Articles                 My Blog

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-001
2017 Forester FB25 Engine
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-002
Driver Side - 12V Battery
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-003
Loosen Negative Terminal

This automotive maintenance tutorial was specifically written to assist owners of the fourth generation (2014, 2015, 2016, 2017 and 2018) Subaru Forester SUV in checking or changing the spark plugs in the FB25 2.5 liter four cylinder boxer engine.

Owners of other Subaru vehicles such as the Outback, Impreza, Legacy, XV Crosstrek, WRX, BRZ, SVX, Tribeca, Exiga, Trezia, Levorg and Baja may also find these DIY instructions to be helpful.

The OEM spark plugs are the NGK SILZKAR7B11 laser iridium.

A few other compatible replacement spark plugs with their part numbers are as follows: Autolite XP5683, Denso (4712) IXEH22TT, Pulstar gg1h10 and Champion 9412.

The tools and other items needed to complete this procedure include an 8mm socket or a flathead screwdriver, a 10mm socket, a 1/4" drive ratchet, a 14mm spark plug socket (or a 9/16" spark plug socket), a short 2" or 3" extension bar, a pair of needle nose pliers and a tube of dielectric grease.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-004
Pull Off Negative Terminal
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-005
Pull Off Wire Fastener
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-006
Cover & Tuck Away
If this is your first time checking or changing the spark plugs in your Forester, I highly recommend removing the 12 volt car battery on the driver side and the engine air filter box on the passenger side.

Taking the extra time to remove those items from the engine bay will make the job much easier to complete. It will also be much safer on the driver side since you will eliminate the possibility of being electrocuted by the 12V battery.

When I repeat this process in the future, I believe that it can be done with out removing the battery or air box assembly since there seems to be just enough room to access the ignition coils and spark plugs on both the driver and passenger sides.

If you don't remove the 12V battery, please at least place a thick towel or rubber mat over the battery and avoid making contact with the terminals.

The first two steps are to open the hood and then move to the right (driver) side of the engine bay.

Loosen the negative "-" terminal nut by turning it counterclockwise with a 10mm socket and a 1/4" drive ratchet.

Pull the negative terminal off the "-" battery post, wrap it in a towel and tuck it away on the side of the battery to help prevent accidental electrical contact.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-007
Pull Off Red Plastic Cover
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-008
Loosen Positive Terminal
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-009
Pull Off Positive Terminal
Pull the red plastic cover off the top of the positive "+" terminal.

Set the red plastic cover aside in a safe place.

Loosen the 10mm positive terminal nut by turning it counterclockwise.

Pull the positive terminal off the "+" battery post and tuck it away on the side of the battery.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-010
Loosen Front 10mm Nut
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-011
Remove "J" Hook Bar
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-012
Loosen the two nuts on the top of the battery hold down bar or "clamp" by turning them counterclockwise with a 10mm wrench or a deep well 10mm socket with a 1/4" drive ratchet.
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-013
Remove Rear "J" Bar
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-014
Lift Off Battery Clamp
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-015
Battery Hold Down Bar
Pull the "J" hooks at the bottom of the two bars out of their mounting slots on the battery tray.

Avoid making contact with the battery posts.

Lift the battery hold down clamp off the top of the old battery and set it aside in a safe place.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-016
Battery Heat Shield Box
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-017
12V Battery Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-018
Plastic Battery Tray
Lift the heat shield cover off the old battery.

Carefully lift the old battery out of the engine bay and gently rest it on the ground.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-019
FB25 Boxer Engine
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-020
Driver Side of Engine
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-021
Lower Driver Side
The FB25 2.5L is a "boxer" or "flat four" engine with four cylinders arranged in a horizontal layout with two cylinders on the left (passenger) side and two cylinders on the right (driver) side.
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-022
Spark Plug Ignition Coils
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-023
Remove Plastic Battery Tray
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-024
2 Driver Side Spark Plugs
Lift the black plastic battery tray out of the way and set it aside in a safe place.

Once the 12V battery is out of the engine bay, you'll be able to easily access the two black plastic ignition coil housings on the driver side.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-025
Passenger Side of Engine
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-026
Engine Air Filter Box
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-027
Flip Up Air Box Latches
For easier access to the two spark plugs on the left (passenger) side of the engine, remove the entire air filter box assembly.

Flip up the two metal latches on the top of the air filter housing.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-028
Loosen Hose Clamp Screw
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-029
Pull Off Air Intake Hose
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-030
Remove Engine Air Filter
Loosen the hose clamp by turning the silver metal screw in the counterclockwise direction with either a flathead screwdriver or an 8mm socket with a 1/4" drive ratchet.

Pull the air intake hose off the air box housing.

Remove the engine air filter and set it aside.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-031
Disconnect MAF Sensor
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-032
Squeeze Together Prongs
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-033
Pull Out Wire Fastener
Push in the release tab on the MAF (mass air flow sensor) electrical connector and pull it straight out of its socket.

Use a pair of needle nose pliers to squeeze together the two prongs on the plastic pop rivet fastener for the MAF sensor's wire loom.

Separate the MAF sensor wire harness from the air box.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-034
Rear of Air Box Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-035
Lower Bolt - Front Air Box
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-036
Loosen Counterclockwise
Set the rear half of the air box aside in a safe place.

Removing the front half of the air box is optional if you want even more working room on the passenger side of the engine.

Remove the bolt at the bottom right (driver) side of the front air box.

Attach the 10mm socket to a long extension bar and loosen the bolt by turning it counterclockwise.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-037
10mm Bolt Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-038
Nut - Top Left of Air Box
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-039
Loosen Counterclockwise
Set the 10mm bolt aside in a safe place.

Remove the 10mm nut on the front left (passenger) side of the front air box housing by turning it counterclockwise.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-040
10mm Nut Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-041
Air Box & Resonator Tank
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-042
Resonator / Silencer
Set the 10mm nut aside in a safe place.

Lift out the front half of the air box which is attached to the white plastic resonator tank which acts as an intake silencer.

Set the front part of the air box aside in a safe place.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-043
Passenger Side of Engine
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-044
Two Ignition Coils Exposed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-045
Loosen 10mm Bolt
Once the air box assembly is out of the way, you'll have easy access to the two spark plugs on the passenger side of the engine.

The steps for checking or replacing any of the four spark plugs is the same.

I recommend only checking or changing one spark plug at a time to reduce the risk of having debris enter the spark plug well.

Loosen the single bolt that secures the ignition coil housing to the cylinder block by turning it counterclockwise with a 10mm socket and a 1/4" drive ratchet.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-046
Spin Out Counterclockwise
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-047
10mm Bolt Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-048
Pull Out Ignition Coil
Spin out the 10mm bolt and set it aside in a safe place.

Gently pull the ignition coil straight out of the spark plug well.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-049
Ignition Coil Removed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-050
Spark Plug In Well
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-051
14mm Spark Plug Socket
Rest the ignition coil on the side of the engine.

Try to avoid stressing or pulling on the electrical wires.

In order to remove the old spark plug, you'll need either a 14mm spark plug socket or a 9/16" spark plug socket.

My 9/16" spark plug socket was too long to fit into the small space on the side of the engine, so I pulled out the rubber insert from inside of it and pushed it into a standard 14mm socket.

Attach your spark plug socket to a short 2 or 3 inch extension bar and insert them into the spark plug well.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-052
Loosen Counterclockwise
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-053
Spin Out Old Spark Plug
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-054
Old Spark Plug Removed
Attach the 3/8" drive ratchet to the extension bar and loosen the old spark plug in the counterclockwise direction.

Try to avoid using excessive force to prevent from cracking the ceramic portion of the old spark plug.

If necessary, you can spray a small amount of penetrating oil into the spark plug well and try again a few minutes later.

Once the old spark plug is loose, detach the ratchet from the extension bar.

Spin the old spark plug out the rest of the way by hand.



 

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-055
Inspect Old Spark Plug
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-056
Spin In New Spark Plug
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-057
Tighten Clockwise
Pull the old spark plug out of the engine and separate it from the socket.

Inspect both sides of the old spark plug.

If the electrode end of the old spark plug appears to be ashy white, the plugs might have been exposed to high temperatures such as overheating or they might be the incorrect heat range for your driving conditions or environment.

If the electrode tip of the old spark plug looks grey or is covered in dark black soot, the engine might be burning oil and should be inspected by a professional mechanic.

I recommend buying the genuine OEM NGK SILZKAR7B11 iridium spark plugs that are installed in the Forester at the factory.

Push the new spark plug into the socket and insert it into the well.

Carefully spin the new spark plug in the clockwise direction by hand to prevent it from becoming cross threaded.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-058
Tape - Secure Socket
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-059
To Just Past Hand Tight
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-060
Dielectric Grease
To prevent from having the socket pop off the extension bar and possibly become stuck inside the spark plug well, I like to use some painter's tape to secure it in place.

Attach the ratchet to the extension bar and the spark plug socket.

Tighten the spark plug in the clockwise direction.

If you are replacing the old spark plug after checking it, just tighten it to a small fraction of a turn past hand tight.

If you are installing a new spark plug, tighten it to just past the point when you feel the new crush washer collapse.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-061
Line Up Ignition Coil
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-062
Push In Ignition Coil Housing
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-063
Re-Insert 10mm Bolt
Apply a small amount of dielectric grease to the opening at the bottom of the rubber dust boot on the ignition coil housing.

The dielectric grease will help keep out moisture and debris to ensure a reliable electrical connection.

Push the ignition coil straight back into the spark plug well.

Re-insert the 10mm bolt and spin it a few turns by hand in the clockwise direction to prevent it from becoming cross threaded.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-064
Tighten Clockwise
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-065
Ignition Coil Secured
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-066
Lower In Front Air Box
Tighten the ignition coil bolt in the clockwise direction with the 10mm socket and a 1/4" drive ratchet until it is snug.

Try to avoid over tightening the bolt to prevent from cracking the plastic ignition coil housing.

If you removed the air box assembly, follow the next steps to replace it.

Lower the front half of the air box with the resonator / silencer bottle down into the engine bay.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-067
Front Half Air Box In Place
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-068
Spin In Lower 10mm Bolt
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-069
Tighten Bolt Clockwise
Spin in the 10mm bolt at the bottom right (driver) side of the front half of the air box.

Tighten the 10mm bolt in the clockwise direction until it is snug.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-070 Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-071
Spin On 10mm Nut - Top
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-072
Tighten Nut Clockwise
Spin on the 10mm nut at the front left (passenger) side of the front half of the air box.

Tighten the nut in the clockwise direction with the 10mm wrench.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-073
Re-Insert Air Filter
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-074
Replace Rear of Air Box
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-075
Push On Air Intake Tube
Re-install the engine air filter into the front half of the air box.

Lower the rear half of the air box down into the engine bay.

Push the tabs on the bottom edge of the rear half of the air box into their corresponding slots on the front half of the air box.

Push the air intake hose back on to the air box.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-076
Snap Two Latches Closed
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-077
Push In Wire Fastener
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-078
Re-Connect MAF Sensor
Swing the two metal latches closed over the top of the air box.

Snap the two latches in place to secure the two halves of the air box together.

Push the wire harness fastener back into the hole on the inner edge of the air box.

Push the MAF sensor electrical connector back into its socket on the top of the air intake tube.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-079
Air Box Re-Assembled
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-080
Replace Plastic Battery Tray
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-081
Battery Tray - Driver Side
Lower the black plastic battery tray down into the engine bay with the arrow pointing towards the front of the vehicle.
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-082
Replace Battery & Shield
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-083
Lower In Battery Clamp
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-084
Re-Insert Rear "J" Hook
Lower the 12V battery down into the engine bay and replace the heat shield cover.

Lower the two "J" bars and the hold down clamp over the top of the battery.

Avoid making contact with the battery posts.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-085
Spin 10mm Nut Clockwise
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-086
Replace Front "J" Hook
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-087
Tighten 10mm Clockwise
Re-insert the "J" hooks at the bottom of the bars into their mounting slots on the battery tray.

Tighten the two 10mm nuts in the clockwise direction until they are snug.

Make sure that the battery can't be rocked, slid or moved around in the engine bay.

If you can move the battery, tighten the two 10mm nuts an extra turn or two.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-088
12V Battery Secured
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-089
Push On Positive Terminal
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-090
Tighten 10mm Clockwise
Push the positive terminal on to the "+" battery post.

Tighten the terminal nut in the clockwise direction with the 10mm socket and a 1/4" drive ratchet until it is snug.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-091
Replace Red Plastic Cover
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-092
Push Wire Fastener On Bar
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-093
Push On Negative Terminal
Push the red plastic cover back into place over the positive terminal.

Push the black plastic fastener for the negative terminal cable over the top of the threaded rear "J" bar.

Push the negative terminal on to the "-" battery post.

Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-094
Tighten Nut Clockwise
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-095
12V Battery Replaced
Subaru-Forester-FB25-Engine-Spark-Plugs-Replacement-Guide-096
Spark Plugs Replaced
Tighten the 10mm negative terminal nut in the clockwise direction until it is snug.

Start the engine and listen closely for any strange sounds that might indicate a loose spark plug or a disconnected electrical connector.

Be sure to record the spark plug change in your vehicle's service records.

If you removed the 12V battery, please remember to adjust the time on the clock and program your favorite radio station presets before you start driving.

For more, please check out all of my 2014-2018 Subaru Forester DIY Repair & Maintenance Guides.
 

If you found this guide to be helpful, please consider making a small donation by clicking on the PayPal.com "Donate" button located to the right of this paragraph. Thank you!
(Note: I am not a registered charity. Donations are not tax deductible.)

Please help support this website by shopping at Amazon.com. Thank You! 

Main Menu            Home            My Digital Cameras            Misc. Pictures            Articles            My Blog

 

Google

Copyright 2017 PaulsTravelPictures.com
 All Rights Reserved