An engine has a hollow, metallic clatter when started cold. The noise diminishe

A hollow, metallic clatter when starting a cold engine that diminishes and eventually goes away as the engine warms up to operating temperature is a common issue. The noise could be caused by several factors, including piston slap, valve train noise, or timing chain noise.

Piston slap is caused by a piston rocking back and forth within its cylinder. The noise sounds like a muffled bell sound or a hollow clatter deep in the engine and is more noticeable when the engine is cold.

Valve train noise is caused by valve and hydraulic lifter noise that has a clicking sound that usually quiets down as you raise the engine RPMs. A lifter is what opens and closes intake and exhaust valves. These noises can be caused by worn or sticking hydraulic lifters. Sticking lifters, in most cases, are caused by a varnish build-up on the lifter surfaces. They may also be caused by low oil pressure (which would cause a hydraulic lifter to collapse). Sticking lifter problems can many times be solved by adding a detergent additive to the oil. If this doesn’t do away with the noise, then the worn lifters that continue to make noise would require replacement. This is not an easy or cheap job and will need to be done by a trained auto repair technician.

Timing chain noise is caused by the timing chains becoming so loose that they whip back and forth against the guides and possibly the timing cover. If the oil pressure is correct, the replacement of the hydraulic tensioners and chain guides would be required. A mechanic’s stethoscope is a great tool to pinpoint this noise. If the noise is loudest when touching the timing cover with the stethoscope, disassembly would be required to confirm and repair the problem. This is a semi-major job for most of these engines and would usually cost in the four-digit range.

It’s best to have a professional mechanic diagnose the issue to determine the root cause of the noise and recommend the appropriate repair.