Why are short journeys considered bad for your car?
Discussion
I've never really understood this. Ok so it might not get warmed up properly so this might cause more wear because the oil isn't reducing friction as much as it might when hot? Or as components in the engine expand with heat they fit together better and so wear less?
Are either of these two ideas even right? Even if they are the same wear would occur while the engine is warming up when starting out on even the longest of journeys.
So why are short journeys bad for your car and manufacturers recommend more regular services for cars that are only used for short journeys?
Are either of these two ideas even right? Even if they are the same wear would occur while the engine is warming up when starting out on even the longest of journeys.
So why are short journeys bad for your car and manufacturers recommend more regular services for cars that are only used for short journeys?
Because short journeys often involve lots of stop/start driving, putting components under load when the oil is cool. The clutch and gearboxes of cars can also suffer under these conditions.
Longer trips usually involve more sustained speeds resulting in sustained higher revs but less stress on the engine and drivetrain.
Longer trips usually involve more sustained speeds resulting in sustained higher revs but less stress on the engine and drivetrain.
As you suspect, when an engine is started the oil pressure needs to build up in order for it to fully protect the engine. Lots of cold starts means lots of times the oil isn't protecting the engine adding to the wear.
Also when the engine is cold the mixture is run rich to aid combustion. This extra fuel can result in bore wash due to it running down the bores washing the oil away. This fuel then enters the sump diluting the oil meaning the oil can't protect as it should. In extreme cases of lots of short runs and cold starts the oil level may rise due to the oil dilution with fuel. You can usually tell if this is a problem as the oil will smell of fuel. Prolonged bore wash will eventually lead to bore wear.
Excessive carbon build up can also occur due to the rich mixture on continuous cold engine use. The carbon will also contaminate the oil.
If you are doing a lot of short journeys with a cold engine you should change your oil more often due to all the above reasons.
As a case in point that cold starting and cold running is the main cause of engine wear take the Mobil 1 E30 325. It was ran for 1 million miles over 4 years continuously on a dyno only stopping for recommended manufacturer service changes.
The engine was then stripped and checked for wear. It had so little wear that it was still within acceptable tolerances of a new engine for most parts and very little wear on others.
http://www.youtube.com/watch?v=gHmMlU8Q-V8
That car is now in the UK (bought by Car Mechanics magazine) and has covered over 1,030,000 miles.
Also when the engine is cold the mixture is run rich to aid combustion. This extra fuel can result in bore wash due to it running down the bores washing the oil away. This fuel then enters the sump diluting the oil meaning the oil can't protect as it should. In extreme cases of lots of short runs and cold starts the oil level may rise due to the oil dilution with fuel. You can usually tell if this is a problem as the oil will smell of fuel. Prolonged bore wash will eventually lead to bore wear.
Excessive carbon build up can also occur due to the rich mixture on continuous cold engine use. The carbon will also contaminate the oil.
If you are doing a lot of short journeys with a cold engine you should change your oil more often due to all the above reasons.
As a case in point that cold starting and cold running is the main cause of engine wear take the Mobil 1 E30 325. It was ran for 1 million miles over 4 years continuously on a dyno only stopping for recommended manufacturer service changes.
The engine was then stripped and checked for wear. It had so little wear that it was still within acceptable tolerances of a new engine for most parts and very little wear on others.
http://www.youtube.com/watch?v=gHmMlU8Q-V8
That car is now in the UK (bought by Car Mechanics magazine) and has covered over 1,030,000 miles.
xr287 said:
I've never really understood this.
With modern cars I doubt the various points others have mentioned really have very much relevance unless you cane the engine from cold. Warm-up is pretty quick these days because low-emissions dictate rapid engine warming. The amount of metal and the volume of coolant in engines is far lower than it used to be. Also engines are made to much tighter tolerances.One of the few remaining issues is condensation leading to water accumulating in the oil of engines which don't get hot enough to evaporate it off over longer journeys. However, this is easily addressed by doing your oil changes based on months in service rather than mileage covered.
So if you change the oil regularly and don't thrash the car from cold you're away and laughing.
As stated above, oil doesn't lubricate properly until it's warm, so on a short journey a greater percentage of the journey is spent without proper lubrication.
It's therefore possible to have a 100k mile car that has less engine wear than a 30k mile car if the 30k mile car has lived in a city and the 100k mile car has lived on the motorway.
For the same reason, it's never a good idea to stress the engine when it's cold, either by using too many revs or loading it up too much by using too much throttle.
It's therefore possible to have a 100k mile car that has less engine wear than a 30k mile car if the 30k mile car has lived in a city and the 100k mile car has lived on the motorway.
For the same reason, it's never a good idea to stress the engine when it's cold, either by using too many revs or loading it up too much by using too much throttle.
All this is also true for cars that do long journeys. Its not as if long journey cars don't go through the cold phase. Both short and long journey car are subject to the initial 10-15 minutes of cold engines.
Chris_w666 said:
Because short journeys often involve lots of stop/start driving, putting components under load when the oil is cool. The clutch and gearboxes of cars can also suffer under these conditions.
Longer trips usually involve more sustained speeds resulting in sustained higher revs but less stress on the engine and drivetrain.
Longer trips usually involve more sustained speeds resulting in sustained higher revs but less stress on the engine and drivetrain.
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