Parts for your 2010 Subaru Forester-Drive belt tensioner

2010 Subaru Forester drive-belt tensioner — is it actually used?

Short answer: on most 2010 Subaru Forester petrol models sold in Australia and New Zealand (the 2.5-litre EJ25), a separate spring-loaded drive-belt tensioner isn’t fitted. These engines run two accessory belts: the alternator/power-steering belt is tensioned by moving the alternator on its bracket with an adjuster screw, and the A/C belt is either a stretch-fit belt or tensioned with a simple manual idler, not an automatic tensioner assembly.

That means a catalogue “drive-belt tensioner” unit isn’t relevant to the common EJ25-powered 2010 Forester. Ordering a tensioner for these petrol variants will usually result in a part that doesn’t install, because the system relies on bracket adjustment and/or a manual idler rather than a spring-loaded arm.

There is an exception. The 2010 Forester 2.0D (EE20 diesel), offered in ANZ markets, uses a single serpentine belt with an automatic accessory belt tensioner. If the vehicle is the diesel, a drive-belt tensioner absolutely applies. So the need for a tensioner on a 2010 Forester hinges on engine type: petrol EJ25 = no separate auto tensioner, diesel EE20 = yes, fitted.

Why Subaru didn’t use an auto tensioner on the petrol EJ25 in 2010? It’s the legacy EJ accessory layout. Subaru didn’t move to a single serpentine belt and spring-loaded tensioner on petrol Forester models until the FB-series engine arrived in the following model year. Until then, belt tension was set manually via the alternator bracket and, for A/C, by a stretch-fit belt or a manual idler. It’s simple, reliable, and keeps parts count down—but it does rely on correct workshop adjustment.

Technical sources referenced for this conclusion include:

• Subaru Forester MY2010 Service Manual (STIS): Drive Belt sections for EJ25 (H4 SOHC) showing alternator bracket adjustment and A/C belt procedures.
• Gates Australia DriveAlign and Micro-V application catalogues: listings for 2008–2010 Forester EJ25 indicate no automatic accessory tensioner, diesel variant lists a tensioner.
• Dayco Australia online catalogue: 2010 Forester EJ25 applications show belts/idlers but no auto tensioner, EE20 diesel lists a tensioner assembly.
• Subaru technical training on FB-series engines: notes the move to a single serpentine belt with an automatic tensioner from the following model year.

Servicing tip for EJ25 owners: instead of replacing a non-existent tensioner, check belt condition, adjust the alternator/PS belt using the adjuster screw (never pry on the alternator body), replace the A/C stretch-fit belt with the correct tool where applicable, and spin/inspect the idler pulleys for noise or roughness.

• Does my 2010 Forester have a drive-belt tensioner?
  Petrol EJ25 models don’t have a separate automatic tensioner, they use alternator bracket adjustment and, for A/C, a stretch belt or manual idler. The 2.0D diesel does have an automatic serpentine-belt tensioner.
• How do you set belt tension on a 2010 Forester petrol?
  Loosen the alternator pivot and lock bolts, turn the adjuster screw to set tension, then re-tighten. Don’t lever on the alternator. After a short drive, recheck tension and listen for squeal. For the A/C belt, use the specified installation method (often a stretch-fit tool) rather than trying to “walk” the belt on with the engine.
• What should be replaced if there’s belt squeal on an EJ25?
  Start with belt condition and tension. If noise persists, inspect the alternator/PS idler and A/C idler pulleys for bearing roughness, and check pulley alignment. On diesel EE20 models, also assess the automatic tensioner for play or a weak spring.