Rod Handsfield

Are the 928 maintenance items mileage or time dependent or both?

In looking at a 928 with roughly 45 K miles I note that the major maintenance items; TB/WP/pulleys replaced & tensioner rebuilt at 22,800 miles. AC lines also replaced, system evacuated & recharged. ALL other belts & cooling hoses changed, cooling/brakes flushed, vacuum lines items were taken care of at around 25 K miles in 2004, were completed 20 K miles and 12 - 14 years ago.
No mention of fuel lines.
thanks, Rod

Bertrand Daoust

Both.

Depending on what your looking at.

If the car was not drive much like here, time is the most important of the two.

45 k miles? Great find Rod.

Adk46

The scientific way to consider your question is to invoke specific degradation mechanisms; components don't just "go bad" over time. Changes in the bulk properties of a material involve time, temperature and optionally various chemical agents. These mechanisms are typically complicated and have complicated relationships with exposure conditions. For some specific bit of exposed material, the conditions are rarely known adequately to predict anything anyway.

This is not true of metals, however: their bulk properties will not change at the low temperatures present in a car. But their surfaces degrade through specific wear and corrosion mechanisms, also hopelessly complicated. A few parts are subject to mechanical issues - e.g., exhaust manifolds may crack due to thermal fatigue.

Mentioning this is of no use to anyone - the point is simply that there's no telling without examination. The "better safe than sorry" approach is wise for some components, but feel free to use your own judgement, budget and philosophy for others.

mickster

Unless the car was garaged in a climate controlled garage and never saw salt on the road, most of the rubber (bushings, hoses, belts, tires at 6 years) will need replacement at nearly 30 years old. The fuel lines are a MUST replace.

James Bailey

If coolant and brake fluid was not changed for 12-14 years that can cause major issues.....

The Forgotten On

General rule is if it is just metal (timing belt gears etc.) , it is a wear part. If it has any plastic/rubber (fuel lines, PS lines, bushings etc.) it is a time/wear part.