How long are 914s supposed to last?, Sorting through the myths Options

[JeffBowlsby]

We like these old cars for our own reasons, but we often hear:

"...remember, these cars [or their parts] were not built to last more than ___ years, they are commodities with a limited useful life." "we live in a throw-away society"...but our cars are not generally disposables with a short time line or priced as such.

I recently saw a Model A with 20K original miles, original paint. At 90-some years old it was a great car for its time and for what it is today. I think the draw is more than just nostalgia, its respect for good design, engineering and an owners regular maintenance.

Todays cars are generally not made from water soluble materials or short life span elements (other than disposable maintenance items) - they have steel not wood chassis, glass not plastic windows, durable leather/fabric not paper seats, etc. With exceptions, generally capable of lasting more than a few years and they cost enough to justify the durability.

Todays manufacturers give warranties of X years, Y miles. All that seems to mean is that they won't pay for maintenance or service after that limited time is up which is just a limitation of liability for those costs, not that the car is only expected to function that long. Not an unreasonable condition of sale, and most cars won't explode when the warranty expires.

Seems counter to the disposable argument that 50-ish years later the original manufacturer still supports these old cars with many factory OEM new parts (albeit of limited selection) and many 914s are still thriving. If it were true that they were only intended to last a certain short period of time, then the mfr. would not be obligated to continue to support them. But they do.

[Superhawk996]

Answer is straight forward in engineering terms.

10 years, 100,000 miles was standard engineering design life going back into the 80's. I'm not sure exactly what VW/Porsche engineering life was in the 70's but it was probably close to that.

That doesn't mean actual vehicle life can't be extended. We've all heard of million mile VW bugs, busses, Volvo's, etc.

Where it gets fuzzy is that in order to demonstrate statistical certainty that the the component will meet design life, it will be designed with a substantial safety margin. In reality, critical parts (LCA, struts, wheels, etc.) are designed to ensure they have multiple design lifes (ranging from 10-100x life). Becuase of this margin, we can reasonably expect a 50 year old part with 200,000 miles PROBABLY won't catastrophically fail. No gurantee but not highly likely.

Likewise, a high mileage rust free chassis may still be functional but you can bet that it isn't as stiff as it once was. Or, that an engine would be down on power, but it is a resonable expectation that the crankshaft will never break on a stock engine and has been designed for multiple design lives.

Here's a quick paper on Weibull life analysis of chassis parts if anyone cares. Literally ton's of SAE papers on this topic out there for anyone really interested.

https://iopscience.iop.org/article/10.1088/...81/1/012057/pdf

[bbrock]

10 years, 100,000 miles was standard engineering design life going back into the 80's. I'm not sure exactly what VW/Porsche engineering life was in the 70's but it was probably close to that.

Which is why I don't think these cars were meant to be "disposable." They were built to last as long as the industry standard and they hit that mark well. Even in the salty Midwest, 914's tended to rust just slightly slower than the engines wore out. By 100K miles, the engine would be ready for a rebuild but the chassis often still had some years left on it even though it would be showing its age. An engine overhaul would extend its life and that is not really built into the design standard as it is intended to provide a service life before MAJOR overhaul of one or more systems components were needed.

On the other side, there are models that just keep going from the era Pete mentioned. Our first new car purchase was a 1991 Nissan Pathfinder. We still have that car and I still drive it regularly as it is pushing 300K miles. I've done some rust repair, replaced the clutch once, and replace a perfectly functioning alternator for a higher output unit to run my snow plow. This car that has never been garaged, rarely washed, and it has been decades since it was waxed has only recently start having the clear coat fail. When I drive it in town, I'm amazed at how many of those old hard body style Pathfinders are still on the road. Just about every parking lot has one I can park next to for comradery. I doubt the engineers who designed these cars were trying to build immortal vehicles, but I doubt the fact that they did makes them unhappy.