Question: I have a 2005 Chevrolet Colorado with the I-5 engine. It's a great truck with 146,000 miles. Should I replace the timing chain/water pump to avoid a catastrophic failure? I'm concerned that the dealer might create more problems than this may avoid.

Answer: In general, an engine's timing chain isn't considered a maintenance item. But in high-mileage situations, a chain may indeed stretch and cause problems. I don't know of any GM dealerships recommending timing-chain replacement on the 3.5-liter five-cylinder engine, without symptoms. The water pump is another story. The pump is often changed along with the scheduled maintenance of a timing-belt replacement (on non-chain engines). It's often overlapping labor with the timing-belt job (might as well change it while you're in there), and a water pump commonly starts rattling and/or leaking before the belt gives way, anyway. In your situation, there's a little bit of a fail-safe built into the powertrain-control system. When the timing chain on the I-5 stretches to a certain point, the PCM will sense the camshaft-to-crankshaft timing getting out of whack, therefore setting code P0014, and turning on the check engine light. A timing chain can also produce a rattling noise when the excessive slack causes it to bounce off the inside of the timing chain cover or block--another symptom to give you a heads-up before the chain lets go. With that said, don't spend the money until you have to.

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