The terms 4WD, AWD, part-time, and full-time get used interchangeably in marketing, but they describe fundamentally different drivetrain systems with different capabilities, maintenance requirements, and driving characteristics. Understanding which system your vehicle has helps you use it correctly and maintain it properly.
Part-Time 4WD
Part-time 4WD is the simplest and most robust system, found on vehicles like the Toyota HiLux, Nissan Navara, Mitsubishi Triton, and Suzuki Jimny. In normal driving, only the rear wheels are powered (rear-wheel drive). The driver manually selects 4WD High (4H) for slippery or loose surfaces and 4WD Low (4L) for extreme off-road situations requiring maximum traction and torque multiplication. Part-time 4WD must not be used on dry sealed roads because the front and rear axles are locked together without a centre differential – on hard surfaces, this causes binding, tyre wear, and driveline damage (called wind-up).
Full-Time 4WD
Full-time 4WD (also called permanent 4WD) sends power to all four wheels all the time through a centre differential that allows the front and rear axles to rotate at different speeds. This means it can be used on all surfaces including dry sealed roads. Examples include the Toyota LandCruiser 200 Series, Mitsubishi Pajero (Super Select in full-time mode), and some Land Rover models. Many full-time systems also have a centre differential lock for off-road use (which effectively turns it into a locked 4WD system like part-time) and a low-range transfer case for extreme conditions.
AWD (All-Wheel Drive)
AWD is typically found on SUVs and passenger cars (Subaru Forester, Mazda CX-5, Toyota RAV4, Hyundai Tucson) and is designed primarily for on-road traction rather than serious off-road use. Most AWD systems are front-wheel drive based and use a centre coupling (viscous, electronic, or Haldex type) to send power to the rear wheels when front wheel slip is detected. Some systems are reactive (they send power to the rear only after the front wheels start slipping) while others are proactive (they pre-emptively distribute torque based on sensor inputs). AWD vehicles generally do not have a low-range transfer case or locking differentials.
Maintenance Differences
Part-time and full-time 4WD systems require transfer case fluid changes and front differential fluid changes in addition to the standard rear differential service. AWD systems with a rear coupling unit require specific fluid for that coupling. Subaru’s AWD system is particularly sensitive to mismatched tyre diameters – even different tread depths between tyres can cause centre coupling damage. Your workshop manual specifies the fluid types, capacities, and service intervals for every component in your specific drivetrain.
Using Your System Correctly
The most common mistake is engaging part-time 4WD on dry sealed roads, which causes expensive driveline damage. The second most common is neglecting transfer case and differential fluid changes, which leads to premature wear of expensive components. Your workshop manual includes the operating instructions for your specific 4WD or AWD system along with the complete drivetrain service schedule. MechanicMate offers PDF workshop manuals for over 960 models at mechanicmate.net/shop.
