This post is a more complete answer to Jonathan's question in my earlier post here: Should I Buy the MU-X or Colorado 7 - UPDATE.
Fascinating analysis of the perceptions and fact. Isuzu promotes the longevity of its 3.0-litre engines with press releases like this:
"Also powering Isuzu’s N Series trucks, the Euro 4 emissions-compliant version in the MU-X produces 130kW at 3600rpm and 380Nm at 1800-2800rpm and comes with a B10 rating of 500,000km, which means 90 per cent of engines are expected to reach 500,000km before requiring a rebuild."
This is a quote taken from the MU-X launch preview in motoring.com.au and I would assume it originally comes from the Isuzu PR department.
As the owner of a 2002 TD Toyota LandCruiser, bought new and now with close to 300,000 trouble free kilometres on it, the concept of an engine with a long life span has real appeal. The 4.2-litre engine in the Landcruiser has conservative torque and power figures. Maybe this is an aid to longevity. I'm a conservative driver, probably rarely use the relatively humble power the LandCruiser engine kicks out anyway. For me, longevity is a huge factor in the decision making process when buying a new vehicle.
I would be fascinated to hear your thoughts on the relevance of ratings such as the B10 that Isuzu quotes. Are they relevant to small vehicles such as an Isuzu ute?
Great website, thanks.
There are two industry standards for measuring engine life. These are called B10 and B50. Each uses statistical methods to estimate engine life. They are not generally quoted for light-duty vehicles, but that doesn't mean they can't be quoted.
Many people think the B10 standard means the point at which 10 per cent wear will take place, and the B50 standard is the point at which 50 per cent of wear occurs. This is not the case at all.
The B50 standard relates to the analysis of when (in distance) 50 per cent of engines will require major repairs, an overhaul, or replacement. B10 is the same thing, only the point when these repairs/replacement are required on 10 per cent of engines.
Major repairs or overhaul means any repair that requires removal of the cylinder heads and/or oil pan.
Obviously the standard is a statistical, standardised analysis which is good for comparison purposes - but it's not a guarantee of how long your particular engine will last. That depends significantly on operational factors.
In the quote above Isuzu has 'sexed up' the language of the B10 standard, by putting a more positive spin on it. Instead of saying 10 per cent of engines will require a rebuild or major repairs by 500,000km the company has stated instead that 90 per cent won't require major repairs/replacement by that distance.
I'm sure the diesel in the Isuzu will be quite durable. Isuzu is a good engine builder - no doubt about that, and this one is artificially limited to low outputs. Also, diesels generally are longer-lived than petrols. This is largely due to the fact that the lower RPMs impose lower stress on the moving parts, and hence wear rates drop.
As to relevance, most longevity claims, however accurate and standardised, are irrelevant to most new vehicle buyers. Most buyers turn the vehicles over in the 3-5 year term, and are generally well under 100,000km when re-sold. So longevity is a largely 'Who cares?' Deal for most buyers - in practise. (Although the idea you're buying a power train that lasts a long time is nice, and it's implied the fundamental engineering is robust to accomplish that - so there's an implied link to reliability.)
Some people do own their new vehicles for donkey's years, so longevity directly affects these owners. Longevity is, however, probably more of a concern for used-vehicle buyers.
It's worth noting that the peak output figures are seldom achieved by engines - the peak power is only ever output with wide-open throttle (meaning, in a diesel: maximum fuel delivery) and only then at those revs and against a balancing load. That's hard to achieve without putting the vehicle on a dynamometer. Likewise peak torque - only at those revs and at wide-open throttle.
So in practise, most driving is done at a fraction of those outputs. As soon as the driver backs off the throttle, less fuel is delivered and therefore less torque is delivered at the crankshaft.
The biggest contributors to wear from a user's perspective are the number of cold starts and servicing. If you want the engine to last for ever, never let it cool down (which is why taxis routinely last 750,000km). Obviously, metal expands when it warms up. This means the critical clearances between the parts, which the oil film covers, is only exactly right at normal operating temperatures. Therefore, most wear takes place,when the engine is warming up. Many short trips (10km to the office, shut down for 8 hours, 10km home, shut down overnight) will wear the engine out at a much shorter distance than 500km a day over the course of a working day.
Conservative driving during the engine's warm-up phase will help reduce wear while the parts are getting their tolerances right. Conservative driving generally imposes less stress on drive trains because lower outputs are generated by the engine. At the other end of the spectrum - in racing, where engines operate at or near peak outputs much more regularly - longevity is the first casualty. Rebuilds are frequent. The funny thing there is: there's not a linear relationship between how hard you drive and the powertrain life: driving like Nanna won't get you much more longevity than driving normally and conservatively, but driving all the time like a Type A driver with rabies will slash longevity. And racing will kill the vehicle even quicker.
Also, oil degrades with time, so changing oil and filter every 10,000km or three months would aid longevity even though the manual generally says six months or 15,000km.
The final point I'd make is about press fluff generally - almost everything in a press release is overstated, even if factually correct. Isuzu might say something about delivering peak torque across a wide range of 1800-2800rpm, but the fact is: that limitation is artificial - imposed by the engine control software because part of the driveline was not able to withstand a greater output reliably. (Isuzu nutters hate it when I suggest this.)
It's up to journos to interpret press releases, but unfortunately few of them have much technical appreciation.