Subaru FA20 Turbo timing chain rattle on cold start: what it is, what to check, what to do

FA20 Turbo timing chain rattle shows up a lot in WRX, Forester XT, and Levorg owner groups. It usually happens on a cold start, lasts 1–5 seconds, then disappears. Owners often describe it as a “chain slap” or “rattle” that sounds nasty, even if the car runs fine right after.

This post covers what owners report, what the likely causes are, and how to sort “annoying but common” from “stop driving and diagnose it.”

What the rattle usually is

Most forum explanations point to a simple idea: the hydraulic chain tensioner needs oil pressure to fully take up slack, and after sitting overnight it can take a moment to pump up again. Until then, the chain can make noise.

Owners commonly report:

• Rattle starts immediately after ignition
• Lasts about 1–5 seconds
• Then goes away and doesn’t return until next cold start

The most common owner theories (and why they matter)

1) Tensioner “drain-down” overnight

This is the big one in owner discussions: the tensioner bleeds down while parked, then needs a second to refill on startup.

2) Oil pressure delay (oil, filter, level, temperature)

A bunch of threads link startup rattle to low/slow oil pressure build, especially in cold temps.

3) Guides/tensioner wear, not the chain itself

When owners talk about fixes, they usually talk about tensioners and guides more than the chain.

When it’s probably “common” vs when you should worry

Often “common” pattern

• Only on cold start
• 1–3 seconds (sometimes up to ~5)
• No check engine light
• No drivability issues after startup

Red flags that need proper diagnosis

• Rattle lasts longer over time (trend is getting worse)
• Rattle happens warm, or at random stops/starts
• You get cam/crank correlation codes or timing-related faults
• You hear knock-like noise that doesn’t clean up quickly

If you’re not sure which sound you’ve got, take a 10–15 second video on a true cold start. That’s the fastest way to get a useful opinion from a Subaru shop.

What owners try first (low effort, low risk)

These won’t “fix” a worn component, but they can reduce the rattle if oil pressure build is the driver.

Check the basics

• Oil level on flat ground, engine cold
• Correct oil grade for your climate
• Use a quality oil filter (owners regularly call out filters in oil pressure/timing discussions)

Tighten your oil-change habits

Owners consistently report that clean oil helps chain/tensioner behaviour. It won’t repair a tired tensioner, but it can reduce symptoms when things are borderline.

A popular owner hack: “prime” oil pressure before starting

Some WRX owners mention a trick: hold the accelerator pedal down before starting so the engine cranks/doesn’t fire (varies by model), giving a few seconds for oil pressure to build, then start normally. People say it reduces the rattle.

Two notes:

• I can’t guarantee this works the same on every FA20DIT ECU setup.
• If your rattle is getting worse, don’t rely on hacks. Diagnose it.

If you’re planning to fix it: don’t do the job twice

If you end up opening the front cover / timing area, owners repeat the same hard lesson: replace the “small stuff” at the same time.

That means:

• Seals
• O-rings
• Any known leak points you’re already staring at

Because the labour is the killer, not the parts.

What to tell your mechanic (so you don’t get brushed off)

Walk in with:

• A cold start video
• How long the noise lasts
• How often it happens
• Any recent oil changes, oil type, and filter used

Then ask them to check:

• Oil pressure behaviour (especially on cold start)
• Timing system condition if there are codes or long rattle events

The Roo Racing take

FA20 Turbo timing chain rattle can be “normal-ish” in the sense that lots of owners report it.
But don’t ignore patterns:

• If it’s getting longer, louder, or more frequent, treat it as a warning.
• If it’s mixed with codes, oil pressure concerns, or knock-like noise, stop guessing and get it checked properly.