The length of service for an automobile is typically measured in distance as measured by the same transmission sensor as the speedometer, but that doesn't serve as an accurate indication for the real service the engine has experience. (The lower gears and stop-and-go nature of city driving can take its toll on an engine in fewer miles than highway driving.)

Heavy equipment manufacturers solve this problem by rating equipment in hours. This is accurate for many machines because they spend most of their time at a particular engine speed, and the life in hours corresponds almost 1:1 with the number of revolutions the engine makes.

Cars are different, though. A car can spend hours at 3000 rpm or 1800 rpm depending on the speed. Accelerating the mass of the car requires even higher engine speeds, and idling is done at about 800 rpm.

Proposed is a second metric for automobile life: an indicator for the number of engine revolutions. The ratio of this number to the number of miles (or kilometers) can also serve as a good indicator for which gears were used more often.
-- kevinthenerd, Aug 17 2011

Hobbs Meter http://en.wikipedia.org/wiki/Hobbs_meter
[Klaatu, Aug 23 2011]

Whether by design or by flaw, the hourage meter on my M35 (which also has an odometer) runs slightly faster at highway speed than it does at idle or tooling around in the woods. I've always assumed it to be a bad design or malfunction, but now I'm thinking it might have been engineered that way for this very purpose.
-- Alterother, Aug 17 2011


Agreed, there ought to be a better method than miles. I worry that people might try to game this by running at lower RPMs. Doing that will lug down the engine, which I heard can cause additional engine wear. On the other side, idling probably causes much less wear per revolution than driving, so this will overestimate the wear in a commuter car that is stuck in traffic for most of it's life.

I wonder if total fuel consumed might correlate better than total revolutions. Or maybe we need to record distance, revolutions, total hours of operation, fuel consumed, total number of gear changes (while accelerating and while not accelerating), percentage of time and precent of fuel consumed in each gear. Then develop a standard computer model to predict engine wear based on those... Of maybe not :)
-- scad mientist, Aug 17 2011


This isn't a great reflection on how long the vehicle will last, either, as wear is also a function of torque and speed. Some overworked engines will give out sooner, some will last much longer. Some military vehicles are designed with industrial-grade commercial engines and designed to only go 20,000 miles before a scheduled rebuild, but those 20,000 miles are the hardest 20k that that commercial engine model will ever see.
-- RayfordSteele, Aug 17 2011


I would actually like a many-digit counter on the dashboard that clocked up individual revs.
-- MaxwellBuchanan, Aug 17 2011


That would either reset every fiew minutes, or it would be a very, very long readout...
-- Alterother, Aug 17 2011


Make it logarithmic ?
-- 8th of 7, Aug 17 2011


No, has to be linear, with the last digit a blur.

OK, 3000rpm for, say, an hour a day average, over a 10-year lifespan, is under a billion.
-- MaxwellBuchanan, Aug 17 2011


In their zealousness for over engineering everything to the point of absolute annoyance, I think BMW have some nag that changes the service interval based on a very simlar concept (meanwhile reducing the power output of the engine until you obey).

This simple gauge would be more fun; and even better: you could ignore it when it signalled for a service!
-- Ling, Aug 18 2011


//the life in hours corresponds almost 1:1 with the number of revolutions the engine makes.//

Your equipment must be extremely highly geared.
-- AusCan531, Aug 18 2011


Perhaps he's an horologist.
-- mouseposture, Aug 18 2011


A measurement of the number of revs the engine had done wouldn't be comparable between different engine models - e.g. some engines are designed to rev much higher than others. I think a more interesting measurement would be an odometer which sampled the absolute value of acceleration every second and added together these values. Thus, short journeys and harsh acceleration or braking would contribute a lot to the total, whereas idling at traffic lights and long, steady motorway journeys would not.
-- hippo, Aug 18 2011


This is virtually redundant for modern vehicles. The powertrain is not often the first thing to fail. The scrapyards are full of cars that are crashed, rotted to the point that they are not roadworthy, or suffer from the failure of a number of secondary systems such as window / door mechanisms, wipers, lights etc.

I like Max's idea. I had a similar idea for a bike I'm building with a 1950's long stroke single cylinder engine. It ticks over at less than 200rpm, so the last figure on the (mechanical) display would be legible.
-- Twizz, Aug 18 2011


Planes have a timer on the tach that only ticks when you are above a certain RPM, so they won't rack up time while you are at idle. Then they have the Hobbs that counts total time.
-- DIYMatt, Aug 18 2011


On further consideration, an integrating count of the quantity of fuel consumed over the service life of the engine is probably a fairly good measure of the amount of "work" done, whatever mode the powerplant is actually running in.
-- 8th of 7, Aug 18 2011


Standard computer model based on N variables... why not? Throw together an ISO document (or other open standard) and have an output variable "x" with some sort of bullshit unit for public consumption, and bingo... a user-friendly alternative to mileage. (Plenty of people drive cars without the foggiest idea of pdV, and I don't see how the result of a black box 100-term polynomial would be any different.)
-- kevinthenerd, Aug 23 2011


// On further consideration, an integrating count of the quantity of fuel consumed over the service life of the engine //

My dad's GMC Sierra shows this in its digital dash dookickey. You can flick through it and learn at least a dozen things about the vehicle's current status that are of interest exclusively to Halbakers.
-- Alterother, Aug 23 2011


Can anyone fathom why an odometer doesn't measure smells?
-- MaxwellBuchanan, Aug 24 2011


For the same reason a fathometer doesn't measure odds.

Please, do try to keep up.
-- 8th of 7, Aug 24 2011


[MaxwellBuchanan] Didn't you mean to ask \\Why doesn't an osmometer measure smells?\\?
-- mouseposture, Aug 25 2011


Baked by Cadillac. The Oil Life Monitor looks at the type of miles done, cold/hot, fast/slow, etc.
-- marklar, Aug 25 2011


//Please, do try to keep up//

Well then, smartarses, explain why a nanometer doesn't measure grandmothers. Pah!
-- MaxwellBuchanan, Aug 25 2011



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