1. Simplicity: The anvil is the simplest machine - one part, no moving parts, and nothing to wear out. And it rarely does. Once you add that second part to any machine, reliability suffers.Early cars were simple - splash lubrication (no oil pump), thermosiphon cooling (no water pump), gas tanks mounted behind the firewall (no fuel pump). A very simple design - not long-lasting, nor very safe, of course. And these early cars had to be simple for a reason - they did not last long. Cylinder walls would score and engines would burn oil, in very short order. The quality of materials and manufacturing processes were primitive, so simplicity was the way to make these early cars even remotely reliable.Simplicity is the ultimate solution, but does not provide much in the way of features, such as safety features, emissions controls, and the like. Moreover, while simple systems maybe robust, their overall lifespan (between overhauls) may be shorter. Old flathead engines were simplicity in themselves, but did not run as long as modern overhead-valve motors.But in general, the simplest systems are the best and most reliable, even if they are not as useful or long-lasting as some more esoteric designs. Ask yourself if you really need all the high-tech gizmos in your next car or washing machine. Some, like parking sensors and backup cameras, could be useful. Others, like powered headrests, seem less so.
2. Redundancy: Two engines sounds better than one, but in practice it not always is such a swell idea. Years ago, regulations required at least three engines on airplanes flying over the oceans. Many airplane makers used four engines, as mounting three proved problematic. However, this was an expensive solution and required a flight engineer to ride herd on all the gauges and settings for four engines. It also provided a false sense of security, as if even one engine was lost, often the plane would lose altitude and hit the ocean before it could land.Three engines seemed like a good compromise, but of course, mounting that third engine was tricky, in terms of weight balance and thrust. And when that third engine went blooey, it could take out control cables or damage control surfaces. Better to let them hang off the wings.Today, regulations have changed, and we allow two engine aircraft to fly over water. Reliability of three- and four-engine aircraft has not been shown to be higher than two-engine aircraft. And in a perverse sort of reverse logic, some argue that the two-engine aircraft, having fewer overall parts is thus more reliable. And there is some truth in this.Many argue the same is true for boats. If you own a boat with two engines, it is not necessarily more reliable than a single-engine boat. You just double all of your maintenance expenses (right down to oil changes) and actually decrease reliability, as there are more things to go wrong.
3. Instrumentation and Sensors: Putting sensors all over a machine to monitor its condition sounds like a great idea as well, but often works less well in practice. For example, a sensor goes bad and sends a false signal. The machine is taken out of service to track down a fault in the sensor system. Or, worse yet, some fault in the sensor causes a problem with the machine.An old-style mechanical oil pressure gauge, for example, could leak, showering the occupants of the vehicle with hot oil and also draining the crankcase over time. A simple "idiot light" seems less desirable, but is actually more robust and easier to use - and more reliable in service. Aftermarket gauge kits don't make a car more reliable, but rather less so, as installing them requires tapping into electrical lines and pressure lines - each of which creates a potential failure point.
OBD II cars were much more complex than their OBD I predecessors. However, since they measure and monitor many more car systems, they tend to "cry wolf" a lot more and issue spurious "check engine" light alarms. Such complexity is probably inevitable, if we are to continue to use internal combustion engines. Learning how to read and diagnose the check engine light is a good idea. But as complex as such systems appear to be, in reality, they have fewer moving parts (or parts, period) that their predecessor carburetors and points ignition.
4. Service Intervals: In the old days, one way to insure reliability was to take apart a piece of machinery every so many miles and rebuild it, or at least inspect it for wear. The theory was, since these parts would wear out anyway, why not rebuild them before they fail, thus insuring optimal reliability?The problem with this theory is that often "perfectly good" parts are discarded and unnecessary services are performed. And in addition, whenever you take apart a product, there is a chance that you will introduce a fault, in addition to fixing others.A recent statistic in Sport Aviation is illustrative of this Waddington Effect: 75% of all catastrophic engine failures in General Aviation aircraft occur within two years or 200 hours of an engine being built, rebuilt, or torn down for inspection. In other words, this theory of reliability can actually introduce more unreliability into a system.
Before you go and "over-service" your car to make it "more reliable" by bolting on aftermarket parts, think about where you are going with this. The old adage "if it works, don't try to fix it!" is very true.