Can you help with some thoughts I’ve been having with regard to my next (diesel) car, which I shall plan to keep for quite a few years, during which I expect to be driving around 110 miles a day, five days a week, in the course of my job managing a number of company branches, for which I’ll be paid a decent mileage rate. Plus there will be some leisure mileage at the weekends, and UK touring holidays. The economics of this all look very good if I can run a new car up to around 200,000 miles. So, all things remaining equal, assuming similar driving patterns, and with the specified servicing intervals, what size diesel engine would last longest and be the best for a 200,000 mile target, without any major problems ñ a three cylinder 1.4-litre, a four-cylinder 1.6-litre, or a four-cylinder 2.0-litre diesel? Or would there be no significant difference? I’m not too bothered about absolute performance, but I do love my driving, as you’ve probably guessed.

Sam Connell

A very interesting question Sam, and it has considerably exercised my grey matter! In terms of lasting longest, I guess you mean either up to when the engine needs a complete rebuild, or perhaps until it falls to pieces. I’m certainly not that sure what effectively terminates the life of most (diesel) engines, but with today’s best oils, and regular maintenance, most engines should go beyond 200,000 miles, and you’re probably going to hit that in around seven years, so your question is certainly relevant.

Looking at the engines you mention, I would focus on what you describe as “similar driving patterns” and suggest that probably the two smaller engines will exercise more revolutions per mile, per year, or whatever, than the 2.0-litre, and the 1.4-litre more than the 1.6-litre, on account of their relative power outputs and likely overall gearing. With your high commuting mileage I’m presuming that a decent proportion of it is on faster roads when you’ll be cruising at a decent speed. If that’s the case, the smaller engines will also generally work a bit harder all the time, but that does not necessarily mean that they will wear out more quickly – and again, which bits of the engine are likely to wear out? I mustn’t get too deeply into this, because in some areas I don’t have any answers! But take your 1.4-litre three-cylinder engine; it has a shorter and stiffer crankshaft than the four-cylinder engines and its bottom end bearings may last longer than those of the other two bigger engines. Then again, if the driving pattern of all the cars is identical, and cruising at steady legal speeds does not require any of them to work that hard, then the smaller engines may have what I’d call a healthier life than the 2.0-litre engine.

Enough of speculations though. I think I’m going to duck out of a truly definitive answer by giving you an answer that you did not actually request. If you take any of these engines and change the oil and filter twice as often as the specified service intervals, then all of them will last longer than any of the engines serviced at standard regular intervals, or on the usual computerised interval basis. Manufacturer specified oil service intervals are necessarily something of a compromise between cost, convenience, and engine life, and are generally generated to satisfy fleet operators for whom cost is the major factor. If a company has a policy of changing its fleet cars every 60,000, or maybe even 100,000-mile intervals, then it has little interest in whether they last much beyond those mileages. As a private owner who might wish to run their car to very high mileages though, which in your case means that you’ll probably crack 200,000 miles in around seven years, the game changes.

Giving a car an extra oil service in between scheduled services is most attractive if you are of a DIY bent, and you can either do all of your oil services, or possibly just the proposed extra in-between oil and filter changes. At your annual mileage of around 30,000, you’ll need two scheduled oil services a year, and therefore what I’m suggesting is two extra ones, meaning an oil service every three months, or 7,000 to 8,000 miles. Each would probably cost you around £50 to do yourself, or maybe £80 to £100 at an independent garage, and as much as £150 at a franchised dealer. You need to think and make a good decision on how and when you get these services done, and your transport needs, if you don’t decide to do it yourself, maybe at weekends.

I hope these suggestions help you decide what to do, but I think that planning a good service schedule like this is as important as the engine size, or anything else about the car, except possibly how you drive it! Regards,

Doc D