Mitsubishi Outlander: 4B12 Timing Chain Tensioner Rattle on Cold Start

The 4B12 2.4-litre naturally aspirated engine uses a hydraulic timing chain tensioner that relies on oil pressure to maintain chain tension. When the engine has been sitting for an extended period, oil drains back from the tensioner, causing the chain to go slack momentarily on start-up. Over time the tensioner's internal check valve wears, and oil drainage between starts worsens. A worn tensioner produces a pronounced chain rattle lasting several seconds on cold start. If ignored, chain slack causes guide rail wear, and in severe cases the chain can jump a tooth on the VVT sprocket, causing misfires or catastrophic valve-to-piston contact. The guide rails themselves are plastic and become brittle with age, compounding the risk.

• Metallic rattling from the top-front of the engine lasting 2–10 seconds on a cold start, then quietening
• Rattling that persists after warm-up, indicating guide rail or tensioner damage beyond normal slack
• Occasional misfire codes (P0300 series) if the chain has jumped a tooth on the VVT sprocket
• Check Engine light with VVT-related codes (P0011, P0021) pointing to camshaft timing deviation

1. 1

   Start the cold engine and listen immediately for a metallic rattling from the top-front of the engine lasting more than 1–2 seconds before quietening.

2. 2

   A healthy tensioner should be virtually silent from the first crank.

3. 3

   Inspect the oil cap underside and valve cover interior for sludge, which accelerates tensioner wear.

4. 4

   Pull service records to confirm regular oil changes; the 4B12 is particularly sensitive to extended intervals.

5. 5

   On a warm engine, a continuing rattle indicates the tensioner is already failing and guide rails may be damaged.

Parts involved: Timing chain.

$900 to $3,200 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Does the engine make any rattling noise on a cold start before it warms up?”
• “When was the last timing chain tensioner service or inspection carried out?”
• “Are there any stored engine fault codes, particularly for camshaft timing?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.