Preventive Maintenance
Failure to carry out preventive maintenance services such as getting parts checked and greased when and where necessary etc. Not checking, topping up and changing fluids such as coolant for the radiator, engine oil etc when necessary and at the appropriate time can cause more damage than you can imagine.‎

Driving Hard On A Cold Engine

When you just start a car in the morning or after a period of rest, you need to understand that the oil would have cooled down and thickened and as a result wouldn't flow freely, you have to let the engine warm up so that the oil would get hot enough and as we all know hot oil flows freely.

Short Journey

Short trips aren't good for the engine because it doesn't allow the engine get hot enough to burn off "soot", water vapor etc in the engine oil and as a result can lead to sludge which is a terrible thing for a car's engine.
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Not Allowing The Turbo Charger Cool Down

For those that have turbo chargers in their cars, the turbine in the turbo charger receives oil for lubrication of the shaft only when the engine is running, so it's best to let the turbo cool down before turning the engine off (this is for those that like to rev just before turning off the engine).