Modern engines do not need to be warmed up, especially diesel engines. On the old carburetted gasoline engines, yes. A cold carb especially on the old VW engines "ice up" on startup especially when there's lots of moisture in the atmosphere. But on fuel injected engines, a good 30 seconds is sufficient.
What's important during start-up is for the oil to lubricate the engine fully before applying any load on the engine. Drive slowly during the first few kilometers to bring the engine up to operating temperature (that includes the engine oil).
Turbines need to be cooled down if:
1) You have been driving in excess of 100 kms constantly for about 30 mins.
2) Your vehicle is carrying extra load or towing a trailer.
One and a half minutes of cooldown is sufficient. Refrain from idling the vehicle excessively. This only wastes fuel and low oil pressure is not good for the engine.
One thing that I may add to save fuel is to PROPERLY inflate the tires on your vehicle, and install the RIGHT SIZE TIRE. I've seen a lot of people in the Philippines oversize their tires for aesthetics and lowering the tire pressure to give them a softer ride, but the results are not good. Oversized tires and low tire pressure put strain on the engine, drivetrain, and could make the vehicle unstable and stop longer.
Tire data is found usually on the driver's door of the vehicle. Follow what the tire data says and it will give you the comfort, stability, fuel economy and performance. Fuel savings could come to as much as 5%.
Check your air filter regularly and replace if dirty (especially on turbocharged engines). Use the right viscosity oil for the vehicle based on the ambient temperature, and change the oil every 5,000 kms or 6 months, whichever comes first. Cut the oil interval to half if you're always carrying heavy loads or towing a trailer.
