By now we all know that an engine lasts much longer if used on long trips rather than short runs, but what exactly is the reason?
Take an extreme example:
Car A does a 4-mile round trip to the shops every day.
Car B does a 40-mile commute everyday on fast roads, and passes the shops on each journey.
Car A therefore does 1,000 miles pa, all cold, BAD; Car B does 20,000 miles pa nearly all hot,GOOD.
But all long journeys start off as short ones, so if Car A has suffered wear from running cold with petrol washing the oil off the bores, so has Car B for the first part of each trip. Physical wear cannot be reversible however long B's trip.
So is this theory of dry bore wear really true? Isn't it much more likely to be the case that corrosive chemicals accumulate in the oil in the condensation in a cold engine, but are largely driven off again when the oil gets up to full temperature?
So the wear caused to engines used on short journeys results from them running and sitting in a corrosive oil/water cocktail, not from the 'choke out' effect?
Any experts care to comment on this?
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I'm no expert Cliff, but I think you've answered your own question.
Both car A and B will suffer the same amount of wear on first starting, but Car A will accumulate corrosive chemicals, sludge etc in the oil due to it not getting hot. The cat will also suffer. Thus the first start wear will get worse over time for car A compared to car B. Once hot, engines driven within their normal rev range suffer little wear if regularly serviced.
Even discounting the accumulation of acids etc, in your example the cars would have the same amount of wear, but Car B will last 20 times as many miles, thus the cost per mile before it is worn out is much less.
I hope this makes sense!
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Also add that condensation will accumlate in the exhaust and rust it through from the inside, brakes will get rusty and pitted from underuse.
And probably loads of other things I haven't thought of.
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This is one of the reasons that Merc put forward for electric oil pumps as they run prior to engine start and can run for several minutes if the engine is shut when very hot. Like a quick stop at a motorway service station. I can see it is a good idea I just hesitate about electrically driven pumps. Having said that some power steering pumps are electric and give very little trouble as they do not overwork when engine rpm\'s are higher Regards Peter
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I am very nervous about critical systems (coolant, oil) being operated by electric pumps.
Traditional mechanial oil pumps very rarely fail catastrophically. I can see electric pumps failing due to chaffed wires, corrosion in connectors, motor bearing/brush failure etc. etc. Same applied to coolant pumps - although at least you would get some time to spot overheating and stop.
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But that is the nub of my query - in theory both cars should wear to the same extent, but we all know that in practice car B will last about 10 times as many miles as car A.
Car A would be a very dubious buy if you were hoping to get 50,000 miles from it, but if you saw car B for sale with 100,000 miles it would probably be a bargain and good for another 100,000.
So I am doubting the conventional explanation that most bore wear takes place when the engine is cold, and suggesting that in fact it takes place all the time through corrosion in engines that never get cleared out by prolonged running at full operating temperature.
If this hypothesis is true, it would follow that it is not short trips that do the harm per se, but the failure to balance these with a big mileage at full temperature.
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An interesting query.
Also not an expert, although I have wondered about the same problem before, since our two cars fit almost exactly the two profiles that Cliff describes. ie. the Civic gets a 100 mile daily round trip, the 416 gets a 10 mile round trip, yet they both have exactly the same number of cold starts.
Since both cars are of similar age and now have similar mileage, are similarly powered and maintained with 5k oil changes, perhaps I should be able to offer some real world experience...
However, when I step into either car, if I didn't already know, I swear I wouldn't be able to guess which was which. Having said that, I know which car i feel most confident in.
I suspect that engine design tolerances and precision of manufacture have a large influence.
Ed.
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There's also something about condensation in oil getting evaporated when engine warms up - hence apparent falling oil level on a car usually used for short trips when it is taken on a long trip.
What about diesels which don't need to run rich when cold - something not mentioned in the thread so far - cold petrol engines run richer and use more fuel producing more crud to gunge the engine up whereas diesels run at the same mixture hot or cold, hence one of the reasons for their greater economy on short, stop-start journeys close to home.
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"If this hypothesis is true, it would follow that it is not short trips that do the harm per se, but the failure to balance these with a big mileage at full temperature."
I should have said, the Rover does get a good blast every couple of weeks, so that would seem to be consistent with the hypothesis.
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""Since both cars are of similar age and now have similar mileage, are similarly powered and maintained with 5k oil changes,""
edisdead - I think the crucial fact with your car maintenance schedule are the 5k oil changes, which then does not allow the car mainly on short runs to accumulate too much crud in its oil.
Obviously if you were on 10k oil changes, it would probably be a whole different story. !!!!
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Does this mean that the 216 only gets it oil changed every 2years? (or worse if using a 10k sceduled change). Is water absorption really a factor, or does the oil become contaminated with petrol which will readily evaporate when warmed up? Oil rarely seems to get to greater that 100 deg C. Various people suggest that marginal emmision failures (HC or CO?) can be solved by changing the oil.
I get the impression that this thread will raise more questions than answers! But a good one all the same.
pmh (was peter)
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Apologies folks, I wasn't particularly clear above - the Rover does ~10k per annum, due to ~fortnightly trips of 250 miles as well as its daily short trips. So I do the 5k change approx twice a year. Maybe its 'short journey syndrome' isn't as bad as I first made out.
Perhaps swmbo and I should swap cars every other week to spread the burden of short/long commutes - but I'm not sure I could manage without my auto 'box. ;-)
My almost paranoic attitude to oil servicing is derived from a combination of:
(i) Desire to keep the cars as long as possible. We like them.
(ii) Passionate loathing of blowing a stash of cash on a car in the first place - I want to defer doing it again as long as I can.
(iii) Genes shared with equally paranoic father.
But trying to keep this technical... Given that used engine oil is considered hazardous enough to warrant dedicated disposal sites and non-contact with skin, I would dread to imagine what sort of chemical nasties lurk in suspension. It wouldn't surprise me if they could partly be held responsible for poor emissions, particularly in older engines.
Ed.
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Cliff
"By now we all know that an engine lasts much longer if used on long trips rather than short runs"
Yes thats what we all say but exactly how do we know this?.
The four mile trip to the shops would give an average mileage of some 1500 miles p.a.
Most cars are in the scap yard after 15 years so this car would be most unlikely to show any engine problems.
I'm not saying it isn't true but perhaps overstated that engines wear out more quickly with short runs.
The commonly held view that its better to buy a car with 100k on the clock in a short time is better than buying one with low mileage is not one I would go along with. Given the choice I would prefer the low mileage weekend used as against the repmobile on a thousand per week.
If engines do wear quicker by short journeys your own theory that wear can't be reversed, means that apart from burning off unwanted condensation etc, what else is gained by long journeys other than more wear?.
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I think as long as low mileage car gets a good "blast" of say 20 miles once a fortnight to clear the cobwebs and regular oil changes there is little chance of premature engine death.
Bear in mind that most 15-20 year old cars still on the road today have done relatively low annual mileages. A friend of mine recently aquired an F reg Nissan Blubird with only 30000 miles on the clock (2000 a year) and it runs fine.
I'm a loser, baby....so why don't you kill me?!
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"By now we all know that an engine lasts much longer if used on long trips rather than short runs" Yes thats what we all say but exactly how do we know this?.
But are all 'short runs' harmful to the egine?
I drive about 6 miles to work in heavy traffic and the engine gets pretty hot, with the cooling fan regularly cutting in. (the run time is abut 20 minutes)
You could argue that the engine would not get as hot on a longer run, say, down the motorway with constant airflow through the rad.
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Cliff.
Cold starting and running is the most important aspect of internal combustion engine wear.
0/30 synthethic oil, preheated engines, by-pass oil filtration, minimum 12 mile round trips and oil analysis at 6 months MAY be the way to go.
At 160k my bore pressures are 13 bar. Is this good? I am looking for 400k.
I love to experiment, my oil now has 23k on it.
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A lot is gained, if my theory is correct. A long journey heats the oil up to proper working temperature. This is very very hot, as anyone who has ever scalded his hand draining hot oil will know. Any petrol will have been evaporated, and also a lot of condensed water. Who knows what other corrosive nasties will be evaporated and sucked out by the crankcase ventilation system as well?
These accumulate when the engine is run cold, and are expelled when the engine is hot. This is, I am contending, a reversible process, helped of course by the frequency of the oil changes.
When the cold-run engine is not running, it sits with this corrosive cocktail of oil, water, petrol, dissolved gases, all over its bearing surfaces and bores. The long-distance engine by contrast sits in nice freshly cleaned-out oil.
Have you ever dismantled an engine that has been standing for years ? There are etched marks on the crankshaft journals showing where the lubrication holes happened to have been positioned. I am suggesting that short journeys do cause most wear: not just on the journey, but all the rest of the time when the engine contains dirty oil.
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I can't find the reference, but I recall an article which seemed to point to corrosion occuring on items like piston rings, valves, rocker arms which are not pressure lubricated. Summarising; low mileage, and short trips, imply much time standing around, during which time such items corrode, affecting sealing of piston to bore etc. In contrast, crankshafts, with no metal to metal contact (riding on a wedge of oil) etc wear v. slowly if at all, so long as oil pressure is maintained, and the package of anti-wear additives is adequate against corrosion. Ergo: frequent oil changes are not so irrelevant to bore wear etc. If i can trace the article I'll post a reference.
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