I'm curious, if serviced properly, for example every six thousand mile oil change, what would be the first thing to fail on an engine, my guess would be valve stem seals as they are not metal but I’m not sure.

I understand anything could fail at any time but I’m wondering is it worth servicing my fiesta that's on 270 thousand miles with an oil change every six thousand miles when something like the valve stem seals are likely to fail first. Are valve stem seals preserved much by frequent oil changes?

  • My answer to this question is the answer I gave on this one building a car is all about engineering a highly durable product at a competitive price. If the engine is designed well then bearings, valves / seats , seals , rings, cylinders and other things that wear all fail at the same time. The real question is what is the design life of a new car? Or over the road 18 wheeler? That's based on customer expectations.
    – zipzit
    Commented May 14, 2017 at 20:03
  • 1
    It really depends on the engine and it's design. Every engine design is going to have a weak spot. Here you are focusing on piston driven engines, yet in a rotary engine the rotor seals are the weakest link. Commented May 14, 2017 at 20:04

3 Answers 3


Piston rings are first to wear out most of the time. They are under much mechanical and friction stress, poorly oiled, and subjected to combustion particulates. Valve stems seals are under no particular stress and the oil tends to preserve them.


Mechanically something in the valve train will fail first. Rubber timing chains. Timing gears. Lifters rockers even pushrods if you have such an engine. There is a good chance this will be repairable from hood. That's how it's made.

The first mechanical part to fail will not be a piston ring or crank or anything in the bottom of the motor. The manufacturer would go out of business if the bottom of their motor failed first. No one would buy the vehicle.

The first failure where the vehicle can't move on its own will be starter or fuel pump.

Absolute First failure will be detected by computer something electrical that will cause a check engine light


To answer the second question,

is it worth servicing my fiesta that's on 270 thousand miles with an oil change every six thousand miles

That depends on what you want to do. If you keep servicing the car regularly, it'll keep running until a major problem makes the car uneconomic to repair (i.e. the cost to repair is more than the car's sale value). That might be tens of thousands of miles from now. Even then, 'uneconomic to repair' doesn't mean you can't or shouldn't repair.

If you don't service the car, the major problem will occur much sooner, and it might be catastrophic (engine seizes) rather than major (e.g. head gasket failure).

Estimating a car's remaining lifetime is difficult: it depends not only on the car's make and model, but also on how it was used by previous owners.

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