oil viscosity VOLKSWAGEN JETTA 2015 Owners Manual

Adjust the tire pressure
The proper tire pressure helps reduce rolling resistance as well as fuel consumption.
When purchasing new tires, always make sure that the tires are optimized for lower rolling resistance.
Use low viscosity engine oil
Fully “synthetic,” low viscosity engine oils that expressly comply with Volkswagen oil quality standards reduce fuel consumption. Low viscosity engine oils reduce the frictional resistance on the engine and are distributed more evenly and quickly, particularly when cold-starting the engine. The effect is partic-ularly apparent in vehicles that frequently travel short distances.
Always ensure the right engine oil level is maintained and keep to the scheduled service intervals (engine oil changes).
Make sure the engine oil that you purchase expressly complies with Volkswagen oil quality standards and is the oil approved by Volkswagen for your vehicle.
Avoid unnecessary weight
The lighter the vehicle, the more economical and eco-friendly it will be. For example, an extra 220 lbs (100 kg) of weight increases fuel consumption by up to 1 pint per 60 miles (0.3 l/100 km).
Remove all unnecessary items and unnecessary dead weight from the vehicle.
Remove unnecessary aftermarket components
The more aerodynamic the vehicle, the less fuel it will consume. Aftermarket components such as bicycle racks reduce its aerodynamic performance.
Therefore, remove unnecessary structures and unused rack systems, particularly if planning to drive at higher speeds.