Often people explain that it’s because you ride a cold engine. But a long ride also starts with a cold engine. So how can two 5km trips per day be worse than a two 20km trips per day if an engine starts cold in both scenarios?
Or does this arguments works under presumtion that you ride 100km in 20 short trips vs 5 trips?
In: Engineering
This is usually said referencing many short trips vs one long one.
Assuming the same number of trips it may have some different issues, e.g. if you never get fully up to temp because it’s all short trips you won’t be circulating much coolant and the system can get a little gummed up faster, but the overall wear of an equal number of longer trips will also add up.
Some stuff is also jusy time, not mileage. Rubber seals and bushings only last so long for example.
Fluids, like the oils inside the engine, change their viscosity as they heat up
When the engine isn’t warmed up, those fluids are much thicker, which means they have a harder time lubricating various parts inside them, longer rides gives them time to properly heat up and become thinner so it can provide more lubrication
During short trips, they don’t have enough time to properly heat up before the engine gets shut off, which is also why it’s recommended to drive and wait anywhere from 15 upwards of 30 minutes before you start hammering your vehicle
It’s kind of a tricky one. You’re right in what you’re saying but the idea is if you drive your car for 2 hours continually each day, or ride it for 10 minutes every day, in principle the damage to piston rings etc is identical. But if it’s a choice between driving the car for 2 hours continually each day or 10 minutes 12 times a day, with a break in-between, the latter is arguably worse. This is because you allow the engine to cool, meaning it has to ‘bed in’ all over again.
Plus, it’s not all about the engine. Other components in the car can be potentially worn more with constant, short trips. The battery, for example. Especially if it’s a bit older, it might slowly lose charge and not fully get it back with many small trips.
There’s two primary reasons that I know.
One is what we call “heat cycles” – like you say, it’s harder on an engine to run it while it’s cold. If you drive 100 miles in one long trip, it is only run cold once. But if you drive 100 miles in short, five mile trips, it is run 20 times while its cold. Those 20 cold starts are a lot harder on the engine than the single one done on the long trip.
The other is the nature of driving on long trips vs short ones. Engines love to run for long periods of time at a steady speed. On long trips, you tend to drive on the highway, averaging roughly the same speed for long periods of time. In short trips, you’re probably in traffic. Stopping, accelerating from stop, stopping again, etc. All that stopping and starting is much harder work for your engine.
Think of it as engine hot/cold cycles. It is better to drive 100 miles on one hot/cold cycle than 100miles on 5 hot/cold cycles.
I think it mostly because short and long trips are associated with different places, and therefore ways of driving. In towns, where you start, stop, turn, bump and whatnot, your car takes a way higher toll on its movable and wearable parts from all the manoeuvring. On the highway, where you maintain a consistent speed, you’re basically only using the engine and wheel axels. No breaking, no speed bumps, no tight turns, no change in RPM — nothing sudden.
That’s why people often separate local miles from highway miles, for example when buying a second hand car.
Add to this some of the details given in other answers, and I think you have quite a full answer to your question.
It’s not so much that the engine is cold , but the fuilds such as oil, transmission, brake, never get warm enough to drive out the accumulated moisture that occurs when the car is setting. This moisture will deteriorate the lubrication and corrosion properties of said fuilds and over time ,can cause failures and rust in critical systems if not replaced on a more frequent basis.
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