When drivers hear the word “idling,” they may think about sitting in traffic at a stoplight or leaving the car running in a fast food drive-thru. Both situations count as idle time, which refers to any period when an engine is running but the vehicle itself isn’t moving. Unfortunately, excessive idling causes wear and tear on your engine, and that stationary time still contributes to your vehicle’s total engine hours.

By definition, the term “engine hours” refers to the total running time of a vehicle’s engine, whether it’s moving or sitting still. That means every minute you spend driving, warming up your car, sitting in traffic, or just idling in a parking lot contributes to the overall total. Idle hours are simply the portion of that running time spent while your vehicle isn’t moving.

Engine hours are so important that many commercial businesses track them for their vehicle fleets. This is because mileage alone, even in a used diesel truck, isn’t a proper measurement of just how much wear and tear a vehicle’s engine has actually experienced. For example, two cars with similar mileage can have very different engine hours, depending on how they were used. In some cases, heavy idling can add a lot of engine time without adding that many miles overall.

Continuous idling can lead to a decrease in engine efficiency over time, along with other internal engine issues. That’s because an idling engine is running without the same working load and operating conditions it experiences during normal driving. Without that heat and pressure, the engine’s combustion cycle is less efficient, and internal conditions become less ideal. This is especially true for modern diesel engines, which are designed to perform best while under load.

Idling can eventually lead to carbon buildup in key engine components, including the vehicle’s exhaust system and engine cylinders. It can also reduce oil quality over time. That’s because fuel can mix with the engine oil during low-temperature, low-load operation. This affects how well the oil lubricates and protects internal engine components.

However, mechanical issues aren’t the only problems caused by too much vehicle idling. Unnecessary idling means more harmful exhaust fumes are produced, which contribute to both air pollution and impact the climate. An idling vehicle is also wasting fuel, which can get expensive over the long term. 

Four-wheel drive (4WD) systems can be pretty capable in situations where front-wheel drive and rear-wheel drive vehicles become hopelessly stuck. Before moving on, let’s first understand the different types of drive systems that exist. Front-wheel drive, as the name suggests, only sends power to the two front wheels, and is known to be fuel efficient. Rear-wheel drive does the opposite, sending power to only the rear wheels, and gives sportier handling than front-wheel drive systems. AWD, or all-wheel drive, can send power to all four wheels, as and when needed, and can even vary the power between the front and rear wheels. 

4-wheel drive is the ultimate setup for off-roading, and drives all four wheels on the car all the time. It’s important to note that in both AWD and 4WD, the mode is not constantly on. Instead, the driver –- or the car -– will activate the mode, and then the effects come into play. Many modern vehicles will be front-wheel drive until the 4WD/AWD mode is activated; for example, this is the case on the Toyota RAV4. However, many drivers tend to treat their 4WD buttons like something magical that makes their vehicle invincible, no matter what the conditions are. Now, this does stem partly from manufacturers marketing 4WD as a foolproof system rather than a tool that requires knowledge to operate. The results can be catastrophic damage and expensive repairs. If you want to avoid such a fate, here are five common mistakes that people make when using 4WD.

One of the classic errors that people unfamiliar with 4WD systems make is driving on pavement or asphalt with the 4WD system engaged. In really egregious cases, these drivers will be driving at high speeds with the system on, which can quickly wreck the entire 4WD setup. This is because 4WD systems are primarily intended for use in situations when traction is reduced -– and only at rather low speeds. 

The issue here is that when you turn your vehicle on the road –- left or right, doesn’t really matter -– the left and right wheels will want to rotate at different speeds. However, the 4WD system will prevent them from doing that. Off-road, in a muddy creek bed, this stress can exit the system naturally because the wheels would “slip” , but this can’t happen on dry, high-traction pavement. The result is something called drivetrain binding, which is also called “wind up” in some parts of the world, and is extremely detrimental to your car. 

Among a great many possibilities, it can make turning feel jerky, make your tires wear a lot faster, apply undue stress to your axles, and even harm the transfer case. The reason this happens is because many of the traditional 4WD setups lock the front and rear wheels together manually via something called a center differential. This is another reason why AWD systems are preferred, because they usually engage automatically when wheel slipping is detected, without much need for user input.

There are usually two types of 4WD mode, known as 4WD high and low range. 4WD high range, usually indicated with a “4WD Hi”, “4H”, or some similar demarcation near the 4WD button, locks the front and rear wheels together without changing any gearing ratios. That last bit is important because the car is still using its “standard” gears, meaning the torque delivery to those wheels would remain relatively normal. This means the car in 4WD high can still move at moderate speeds with little problems, perfect for applications like driving in snow or sand. 

4WD low range, on the other hand, changes things up quite a bit. The low-range refers to a change in the gearing ratios, so that the engine can deliver lots of torque to the wheels at low RPMs . This helps traction significantly, and people who tow things will know how much 4WD low helps in towing something heavy uphill. Also, during 4WD low, engine braking is much higher than normal, so it also helps when going downhill. The tradeoff with 4WD low is that it’s not intended for even moderate speed use, with the most experienced drivers just sticking to a crawl when using it. Using the wrong mode can lead to problems like the transmission overheating, clutches wearing excessively on manuals, drivetrain binding, extremely high engine revs, and just plain old getting stuck –- which is what 4WD was supposed to avoid.

The tires -– and more specifically the tread on those tires -– is as important as having a 4WD system on your car. In fact, we’re willing to say that in most cases, an AWD system with off-road tires will outperform a 4WD system with street tires in the hands of the everyday driver. That’s because street or road-use-specific tires will have a tread that balances traction with fuel economy and noise levels, whereas off-road tires prioritize grip . We cannot stress how important it is to have the correct tires for your particular situation –- snow tires won’t do you much good if visiting Texas in the summer, for instance. 

Even the National Parks Service (NPS) says that tire choice is critical. For example, the NPS says that in order to visit the Mojave reserve in California, the most important item that a visitor needs is “a high clearance 4×4 with tires designed for off-pavement use”, so it’s best to take this seriously. That same NPS page also says that street tires getting ripped up while being used off-road are a significant cause for vehicles getting stranded, along with breakdowns and not having proper ground clearance. 

The NPS also advises travelers to carry at least two spare tires when visiting, of which one is explicitly supposed to be an all-terrain tire. So, don’t take a chance when planning a trip off the beaten track; research your environment thoroughly, choose the right tires, and don’t forget to bring a spare.

As we’ve mentioned earlier, many 4WD vehicles come with something called a differential, which is a piece of the 4WD system that allows the wheels to turn independently or forces them to turn together depending on the setting. Vehicles can have up to three differentials, mounted on the front axle, rear axle, and in the middle of the vehicle, each serving different purposes. 

A front locking diff locks the front left and front right wheels together, making them spin at the same speed. The rear does the same, but for the back wheels –- the rear is arguably more important because the back axle on SUVs can usually handle more weight, thus leading to those back wheels being able to provide more traction. There is also something called a limited-slip differential that is sort of a hybrid option between these, but we won’t get into that. A center locking differential, however, is slightly different, in that it locks the front and rear driveshafts together, with no locking of the left and right wheels -– but should never be used on paved roads unless you want accelerated wear on your vehicle. 

So, with a center diff, the driver gets the choice of choosing whether they want power sent equally to both axles (by using the center diff), if they want the rear wheels to push the vehicle together (rear diff engaged), or both cases together. This flexibility is what gives serious off-road vehicles like the Mercedes G63 and some Toyota Land cruisers the ultimate off-road capability, and not using your center locking diff is essentially leaving torque on the table in rough terrain. 

If you think about it, the basic function of every 4×4 system is to provide traction in conditions where that traction could otherwise be reduced. In such instances, airing down your tires -– which means reducing the air below the recommended roadgoing PSI -– can help quite a bit, especially on soft surfaces like snow, sand, gravel, and dirt. The primary reason why this helps is because the area of your tire that’s actually making contact with the ground (known as the “contact patch”), increases drastically with lower tire pressure. 

A larger contact patch on one or even more tires increases the surface area that the weight of the vehicle rests on, which in turn means a lot more traction than normal. It also makes it easier to go over small obstacles. For instance, if you’re going over a brick at road-level PSI, the particular tire that’s going over the brick might lift up into the air, leaving a very small contact patch for traction on that particular tire. However, if you air down your tires, the tire “absorbs” the brick, maintaining a large contact patch, and therefore, more traction. Not airing down your tires means that your 4×4 system won’t be delivering the optimum amount of traction to get you out of sticky situations, so it’s best to do so. Some off-road focused vehicles even come with a built-in air compressor for reinflation.