Cold start (automotive)

A cold start is an attempt to start a vehicle's engine when ambient temperatures are much lower than its normal operating temperature. A cold start can be difficult for an engine due to higher viscosity of oil and fuel in cold temperatures.

Generally speaking, diesel engines have more difficulty starting at low outside temperatures than gasoline engines, and electric engines have the most problems. Diesel engines do not use spark plugs to ignite the air fuel mixture and rely only on the heat generated by compression alone to ignite the fuel. In extremely low ambient temperature diesel fuel can gel which can completely stop the fuel from flowing.