I read your article about the Jeep engine replacement. My Buick Century has about the same amount of mileage – 200,000-plus. How long can I expect my engine to last if I keep on driving it? It has had all the scheduled maintenance and seems to perform fine.

I received several comments about the Jeep engine replacement topic, with some folks questioning why such a bulletproof engine might need to be replaced. Others asked the same question you did: What kind of lifespan might one expect in an older engine, and what are the signs of impending failure? Let’s explore this.

The Jeep engine mentioned is a cast-iron in-line six with an enviable reputation for longevity. In blunt terms, it’s an old-school, overbuilt engine, and it’s not vulnerable to corrosion and distortion, which can plague some newer, lightweight aluminum or aluminum/iron engines. An engine such as the Jeep’s might require a valve job and timing chain replacement – perhaps at 150,000 to 200,000 miles – then keep on running until the rest of the vehicle wears out.

A newer engine might run as longer or longer, due to improved design, use of high-tech materials and superior machining processes, but it is more fragile due to greater stresses placed on lighter assemblies. Proper cooling system maintenance is hugely important on newer engines as corrosion can wreak havoc on expensive components, and an overheating incident can pop a head gasket or warp a cylinder head.

Lengthier oil-change intervals are common on newer engines, thanks to superior oil and improved crankcase ventilation systems. Yet clean oil, in the right quantity, is more important than ever.

Let me ask some questions about a high-mileage engine such as yours.

• Are the engine oil and coolant clean? Dark, discolored or stinky fluids are the result of deferred maintenance, and are not a good indicator of carefree miles ahead.

• Is the engine quiet at cold start-up and after? A slight clacking for a short time when cold might be harmless piston slap, but deeper knocking noises such as with a faulty rod or main bearing are big trouble. Ticking sounds are often related to the valve train.

• Does the engine idle and accelerate smoothly? If not, tests should be run of the ignition and fuel systems, and cylinder compression.

• Does the exhaust smoke? Worn valve seals and/or guides are a likely cause, and often require a valve job to fix.

• Has the engine ever overheated? A head gasket failure, or worse, might be on the horizon.

• Is the engine free of oil or coolant leakage? Minor oil leakage is mostly an annoyance. A large oil leak or any coolant leakage can lead to serious trouble.

Virtually all engines will require the camshaft drive to be renewed at some point. Timing belts should be replaced promptly on schedule (60,000 to 90,000 miles) to avoid a possible valve/piston catastrophe. Timing chains will run further, perhaps 125,000 to 175,000 miles.

If your Buick checks out in the above categories, and its timing chain has been renewed, you should be good to go for perhaps another 50,000 miles.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose.