Engine knocking or rattling from cold: causes, seriousness and affected cars

A metallic knock or rattle in the first seconds after a cold start is the most common sign of a stretched timing chain or a tired tensioner. Never ignore it: on many engines, a chain that jumps makes the pistons hit the valves, and the engine is lost.

The most common causes

The timing chain and its tensioner

This is the most cited cause, on many engines:

• BMW 2.0 diesel N47: the chain at the gearbox end can stretch, with a metallic rattle from cold, then a jump and engine failure; the risk peaks up to 2013 (Caradisiac). CarVerif quotes €2,500 to €9,000 depending on whether only the chain or the whole engine is replaced (CarVerif).
• Peugeot, Citroën, DS 1.5 BlueHDi: the 7 mm camshaft chain can wear prematurely and then break; the first sign is a knock on a cold start. Models built up to 31 January 2023 were recalled for a reinforced chain (Fiches-auto; CarVerif).
• Audi and Volkswagen 1.2 and 1.4 TFSI: the chain with plastic tensioners stretches and can jump; an Audi A1 owner reports a rattle at 60,000 km and a €2,400 timing job (Fiches-auto; GetCarwise).
• Audi 3.0 TDI: cold rattles point to a tired tensioner from 100,000 km (CarVerif).
• Hyundai 2.0 CRDi: on the ix35, the chain wears between 80,000 and 120,000 km because of a faulty tensioner, mainly before 2013 (CarVerif).

On the BMW 118d, this cold rattle often comes with fault code P0016 (crankshaft/camshaft correlation) (CarVerif).

Big-end bearings

A knock that appears when warm is even more worrying: on the 2009-2013 1.5 dCi, it is linked to big-end bearing wear (CarVerif).

Other noises that can mislead

• an injector ticking on a cold start (Fiches-auto, Audi A1);
• the turbo wastegate actuator, which can rattle when cold without immediate consequences (GetCarwise, Aston Martin DB11; Euro Premium Parts, BMW 2 Series);
• worn engine mounts, which give a sharp clunk on start-up or gear changes (Auto & Moto Hebdo).

What to do

Do not drive with a pronounced chain rattle (GetCarwise, Audi A8). Have the chain, tensioner and timing diagnosed: a new chain costs far less than an engine.

Before buying a used car

Insist on starting the engine from cold yourself and listen for at least thirty seconds (CarVerif, Mercedes A-Class). Be wary of a seller who ran the car before you arrived (CarVerif, BMW 1 Series F20). Turn down a car that rattles from cold without a clear chain or tensioner invoice (CarVerif, Audi A1).