We all hear the truism that short trips are where much of the engine wear takes place. But does that equate to shortening the life of the engine? I am pretty sure I've come across UOAs here that somewhere in the comments, indicated that much of the driving was short trips, and I don't recall seeing any of these that had incredibly high wear metal results. Usually when that was referred to, the Blackstone comments will be something like, "Even though you said you did a lot of short tripping, the wear metal results were fine." But regardless of a UOA reading, I'm wondering--do cars that do a lot of short tripping, have engine problems earlier? Or do these engines go 200-300K just like the others, with proper maintenance?
Short trips = short engine life?
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Nick1994
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They probably do ok. But people who do short trips probably don't pack on that many miles, so the cars usually age out and everything around the engine block wears/ages out and people dump the cars.
I realize that by definition, short trip cars can easily expect fewer miles. But one SAE study I looked at said wear right after a cold start was 20x the wear at operating temp, so it made me wonder about how that might impact engine life. I'm thinking there is no way that the life of the engine itself could be 20x as short.
The way that's phrased, its really impossible to answer with any degree of substance.
Also, in decades past there were circumstances ( mechanical and lubrication) where there was a higher degree of truth than not to that old truism.
In tribology, wear particle generation comes from multiple sources in different lubrication regimes.
Each of those contributes differently to "engine life" ( which would require a very specific definition and set of qualifications)
With all things equal, hypothetically, I would expect that in "short term driving"( whatever that is defined as)
I would expect to see
more "wear"( however that would be defined) from the loading and thermal shock of repeated ramp ups and downs with any lubrication wear secondarily but directly related to the material shocking.
I base that overall on the documented studies where machines in general last longer in a service life when run in "steady state" for long periods rather than short runs. Even then, these studies are highly anecdotal and rely a lot more on "extrapolation" rather than detailed long term condition monitoring.
Also, in decades past there were circumstances ( mechanical and lubrication) where there was a higher degree of truth than not to that old truism.
In tribology, wear particle generation comes from multiple sources in different lubrication regimes.
Each of those contributes differently to "engine life" ( which would require a very specific definition and set of qualifications)
With all things equal, hypothetically, I would expect that in "short term driving"( whatever that is defined as)
I would expect to see
more "wear"( however that would be defined) from the loading and thermal shock of repeated ramp ups and downs with any lubrication wear secondarily but directly related to the material shocking.
I base that overall on the documented studies where machines in general last longer in a service life when run in "steady state" for long periods rather than short runs. Even then, these studies are highly anecdotal and rely a lot more on "extrapolation" rather than detailed long term condition monitoring.
Hopelessly vague question, I agree. But its one I wanted to ask, regardless. 
I'm suspecting that engines can go to 200,000 or 300,000 miles even if they are primarily short tripped, but if that's not the case, I'd love to see what folks have to say about it.
Reason why I'm asking is that a few days ago, I came across a 2006 SAE study looking at engine wear with different use cases, and four types of oil , and in this study with a 1998 GM 6 cylinder engine, they even used what would now be a 12 grade oil, and even though the wear was higher with that ultra-thin oil, it was still nowhere near the amount of wear, as the same oils did when they did low RPMs on a cold engine. In other words, even what some might term a grossly inappropriate oil for that engine still incurred less wear on the engine, than any oil was, during that initial 10-20 minutes after a cold start. It made me wonder how bad that cold start wear really was, even though the authors of this study stated that cold start wear was around 20 times the amount of wear under normal operating conditions. I am thinking that doing primarily cold starts couldn’t possibly reduce engine life to 1/20 of the life of a vehicle that primarily goes long distances.
I'm suspecting that engines can go to 200,000 or 300,000 miles even if they are primarily short tripped, but if that's not the case, I'd love to see what folks have to say about it.
Reason why I'm asking is that a few days ago, I came across a 2006 SAE study looking at engine wear with different use cases, and four types of oil , and in this study with a 1998 GM 6 cylinder engine, they even used what would now be a 12 grade oil, and even though the wear was higher with that ultra-thin oil, it was still nowhere near the amount of wear, as the same oils did when they did low RPMs on a cold engine. In other words, even what some might term a grossly inappropriate oil for that engine still incurred less wear on the engine, than any oil was, during that initial 10-20 minutes after a cold start. It made me wonder how bad that cold start wear really was, even though the authors of this study stated that cold start wear was around 20 times the amount of wear under normal operating conditions. I am thinking that doing primarily cold starts couldn’t possibly reduce engine life to 1/20 of the life of a vehicle that primarily goes long distances.
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I've noticed a lot of issues/leaks started popping up on my 530i ever since it became a short tripper and I started parking it outside, especially during our cold midwestern winters. Alas, I can't tell if these issues would not appear if I was doing more long distance driving instead. Maybe it's just coincidence.
I'm at 116K miles now. There is no way this car will make it to 200K miles - I'm just not willing to keep dumping money into it to keep it that long.
I'm at 116K miles now. There is no way this car will make it to 200K miles - I'm just not willing to keep dumping money into it to keep it that long.
Hopelessly vague question, I agree. But its one I wanted to ask, regardless.
I'm suspecting that engines can go to 200,000 or 300,000 miles even if they are primarily short tripped, but if that's not the case, I'd love to see what folks have to say about it.
I completely agree with you asking it and the reasons you did- that wasn't my point.
As a lubrication engineer, I get asked that by clients several hundred times a year and I "have to" answer it. ( not on cars mind you but heavy equipment)
So, I have to "define' the question frequently because its not so simple and then people want to hang you with the answers sometimes.
I think back to the 50’s and 60’s and so when most people didn’t drive long distances to work. They mostly lived where they worked. 10-15 minute commutes were normal. Now, anything under a hour is a godsend and people drive all over for vacation and visiting. The Interstate Highway System wasn’t completely done yet and vacations from work were usually a week or two.
This was also the time that getting 100,000 miles on the odometer was a big deal. Along with other factors, cars didn’t hold up as well as they do now.
This was also the time that getting 100,000 miles on the odometer was a big deal. Along with other factors, cars didn’t hold up as well as they do now.
Let me elaborate on that a bit- I've done this with bearing manufacturers for the same type testing. The physics are pretty much the same as is the determination.
A bearings life ( journal or anti friction standard) is solely determined by its running geometry first and lubrication regime second.
If the geometry is wrong, no lubricant in existence can overcome that.
From ambient to operating temperature- there is a period where the bearing thermally normalizes. ( the lubricant directly affects this but is not the only contributor)
During this period is where this 'start up" wear happens. Whether it is surface fatiguing, finish alteration, asperity change or finally 1 or 2 body wear is just a matter of that specific bearing and its condition as to what percentage each is happening.
Then the factors such as mechanical alignment, component stress and others which are external to the bearing exert their forces also.
It takes effort on a test bench with a single bearing to capture and measure all these- in a complete machine it would be virtually impossible ( not technically as much as financially) so people take these bench results and extrapolate.
Like in the example you quote ( and SAE is famous for and I state that as a professional member) that term "engine life" is vague and undefinable. This is one reason industry generally doesn't use SAE guidance because of its vagueness and lack of detailed specificity.
So in a journal bearing, the "oil" would play a part in the thermal cycle but its not the major player.
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It's all relative.
What engine and how is it driven? The short tripped car... is it started and driven for only a few miles in cold temps or warm temps? The long drive car, is it driven on flat lands, in nice weather, at a consistent speed?
I drive long distances but sometimes in heavy stop and go traffic, I encounter a lot of hills, and redline the engine consistently. Is that better than the average short tripper? I don't know.
What engine and how is it driven? The short tripped car... is it started and driven for only a few miles in cold temps or warm temps? The long drive car, is it driven on flat lands, in nice weather, at a consistent speed?
I drive long distances but sometimes in heavy stop and go traffic, I encounter a lot of hills, and redline the engine consistently. Is that better than the average short tripper? I don't know.
This is an excellent overview of 'start-up' wear problems. MANY people consider 'start-up wear' to be related to lack of oil flow right at and in the first several seconds after start-up. While that is a consideration, 'start-up wear' is more about parts fit (geometry) than lube.
Lots of starts and stops wear an engine more than driving across the plains on the highway, but I can't provide data to quantify the difference. (-:
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But then how do you know? Doesn't it all come down to design? Otherwise these start stop systems would've destroyed engines by now.
To a point that's correct but has to be taken in context.
Every complex machine is designed with a fatigue analysis with an S-N curve, cyclic life etc. ( how we determine metallurgy, tolerances, lubrication, heat treat etc.)
One thing that's a universal constant is heat- going from ambient to operational and back down.
Also wear has more than one definition ( loss of mass, loss of finish, loss of geometry, loss of alignment, loss of coating or hardness to name a few)
We know from thousands of materials tests over a hundred years from hundreds of industries how basic and alloyed materials react to most of these stresses. ( properties of materials and statics is a pretty well defined field but like most- always changing)
Tools like FEA help also.
So take the automotive "motif" of start/stop out and just insert ramp up and down from a thermal and stress perspective- we can reasonably state with a high degree ( but not absolute) degree of accuracy that any machine will stress ( wear) faster in the short use mode over a long term use mode with all other variables equal.
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Very informative. Thanks for the great post. It's guys like you that make this forum what it is.
I know you asked about the engine, for me a bigger concern is that given a fixed number of miles, a vehicle that is short tripped and/or driven primarily in a city will show more wear on every part compared to a vehicle that is driven for hundreds of miles at a time on an interstate. When I was driving 40K miles a year, after 3 years and 120K miles, a car/truck still looked, drove, and smelled new, with only regular scheduled maintenance. Once I started driving 6K miles a year, which included 4-6 separate trips in a day, a 3 year old car with 20K miles is similar in condition, and needing more maintenance parts than the 120K mile car. I have not experienced an actual engine failure related to mileage, but I have rebuilt a number of engines over the years. Engines that were run long and hard were typically in better internal condition than engines that were short tripped. This includes both cleanliness and measurements. I cannot quantify the number of hours on an engine driven for many highway miles vs. an engine that is short tripped or driven low miles in a city environment where it may take an hour to go 10 miles vs. 75 miles on a highway. A new york city car is generally in much worse condition at 100K than a texas or florida car with the same miles.
Off the top of your head, the engines that you know (or were told) were short tripped--what would they be in your shop for? Sludge, even though the parts were still functioning? Is that what you meant?
Well your experience is validating the conclusions of the study I was looking at, saying that lots of cold starts & short trips will increase wear (compared to just a few cold starts, & mainly freeway mileage).
Well your experience is validating the conclusions of the study I was looking at, saying that lots of cold starts & short trips will increase wear (compared to just a few cold starts, & mainly freeway mileage).
Short trips can be different too. A parts delivery vehicle does deliveries around town all day long. Short trips but it's warmed up a good portion of the day because of the short time it's stopped for.
Another vehicle could be driven from one house to another, sit there for an hour or more, then on to another place (like a nurse doing house calls or something), so it's getting multiple cold starts all day long. Probably worse than the parts delivery cars usage scenario.
My work truck drives from the office to a subdivision, sometimes 5 minutes away, sometimes 20 minutes away, or anything in between that is typical driving. Once in the subdivision it's warmed up and it sometimes stays warmed up because we use it to drive to different areas near where we're working, or using the AC idling while we're doing field notes or lunch etc.
It sometimes sits for hours between being run but typically stays warm most of the day.
My truck also counts hours so it has 197k miles and roughly 8700 engine hours. Not sure what that's equivalent to in miles but one source gave me a conversion that said it's equivalent to 520k miles.
Another vehicle could be driven from one house to another, sit there for an hour or more, then on to another place (like a nurse doing house calls or something), so it's getting multiple cold starts all day long. Probably worse than the parts delivery cars usage scenario.
My work truck drives from the office to a subdivision, sometimes 5 minutes away, sometimes 20 minutes away, or anything in between that is typical driving. Once in the subdivision it's warmed up and it sometimes stays warmed up because we use it to drive to different areas near where we're working, or using the AC idling while we're doing field notes or lunch etc.
It sometimes sits for hours between being run but typically stays warm most of the day.
My truck also counts hours so it has 197k miles and roughly 8700 engine hours. Not sure what that's equivalent to in miles but one source gave me a conversion that said it's equivalent to 520k miles.
Short trips with DI put fuel in the oil , at least with my mazda. I go heavier , and change often in cool weather.
Here is my experience. Every vehicle I have owned over last 20 years were short tripped by me or wife and each one got replaced in less than 8 years some considerable less. Reason was same across the board problems. They all used oil between changes but electrical problems killed them. Reason is short tripped electronics get used just as much. Problems with engines was carbon, head gaskets, and clogged oil rings. I even had a 300 dollar fuel pump go out on Mitsubishi after sitting for my back recovery from surgery. Forget about ac working for that long. I have since moved but still short tripped but not idling the whole time. 2 years and 14k on Caravan where others would be lucky to get 5k a year.
A couple things. One, quantification of specific individuals is different from proving the general case. Two, I said I couldn't _provide_ the data. That isn't the same as not having it. (-: Three, have a look at the thread about the 3xx,xxx-mile MOPAR engine teardown (I think that was the one), and in particular the posts about start-stop tech and what has had to be done from design and construction points of view to deal with that specific function.
