How highway driving benefits your car 

The more you regularly drive fast, the more you clear the exhaust system of the delaying fumes. PHOTO/ROLAND D. NASASIRA

What you need to know:

Oil and other fluids need to reach a certain temperature to fully lubricate your vehicle and are unable to efficiently do it at lower temperatures. Highway miles also allow the motor to sit at its optimal rpm level as well, which minimises wear and maximising fuel economy.

Although it has UAW number plate series, Evelyn Kusiima’s Toyota Spacio’s mileage is still below 100,000kms, something that could make you think that her speedometre is faulty. Usually, she drives it from her home in Kyaliwajjala, a Kampala suburb, to her workplace in Kololo, Kampala. The longest she has driven it to is Entebbe City.   

Like Kusiima, Elizabeth Namugerwa’s car, also a Toyota Spacio registered with UBF number plate series is below the 80,000 kilometre mark yet she bought it six years ago. She lives in Kulambiro, a Kampala suburb and works in Ntinda, Kampala (a distance of less than 10kms). Like Kusiima, Namugerwa prefers to only drive her car from her home to her workplace.

According to, generally speaking, highway and city driving are different activities for your car. There is a reason why most cars have higher miles per gallon (mpg) ratings when you are looking at highway driving than city driving, and those that have higher city ratings are generally special cases. Simply speaking, the reason behind this is the fact that the vehicle has to work harder in the city due to traffic, stop lights, shifting, braking, hard turns and every other situation that does not exist on the highway where the car gets up to speed and maintains it for a while. 

Complete combustion

Peter Amadi, a mechanic, says the importance of driving on the highway is to build complete combustion, something you cannot get when you constantly drive in traffic jam or built up areas with slow moving traffic. Combustion is the complete burning of fuel and air. Whatever the engine takes in is burnt to the maximum. When complete combustion takes place, the air to fuel ratio will match and your car’s plugs will give you the right sparking at the right time.

The engine should be fully functional, not while in traffic jam where there is too much fuel lying idle in the system. Instead, the more you regularly drive fast, the more you clear the exhaust system of the delaying fumes. This explains why rally cars have through pipes because they have no catalytic converter or silencer and release fumes as they are burnt, unlike ordinary cars that have these components that sieve what is released into the environment.

“When you do not take your car on the highway for maximum combustion, there is dribbling of fuel in the combustion chamber. The fuel is not burnt fully and this means it is wasted. It enters the engine and this is why the reason why usually, the rear end of the exhaust turns dark black. Fuel keeps going into the engine because you are using heavy gears in traffic jam and it is not burnt fully because the vehicle is not moving fast,” Amadi explains.


“You waste a lot of fuel and engine performance is not at 100 percent. This can lead to overhauling an engine because it is not performing as it is meant to. The valves will build up and accumulate carbon because fuel is not burning. Also, the fuel that remains in the engine unburnt changes to carbon because of combustion not taking place maximally. You will end up losing engine power since the valves are not opening fully and are full of carbon. A car that is regularly driven on the highway performs well and better compared to one stuck in urban drives,” Amadi adds.

Valve grinding

Alvin Nkini, a mechanic says valves in the combustion process serve as inlets and outlets. The inlets open for diesel or petrol to go into the engine chamber. After burning, the exhaust valves open to release the burnt fumes through the exhaust system.

That is why there is something called valve grinding. If the valve is full of carbon because of not burning fuel properly, it does not close and this will cause high fuel consumption because fuel will keep flowing to the valves. 

The effects of keeping to urban drives are regardless of whether your car has a small or big engine as long as it has valves and uses fuel. When you eventually drive on a highway, you may experience highway challenges because the car is not used to constant acceleration at high speed and high temperatures at high speed.

“You may end up blowing your radiator because you are not used to high performance. Everything, including tyres and the radiator are moving so fast under high pressure. If the radiator has any weakness, it will manifest on the highway since you have subjected it to temperatures it is not been used to,” Nkini explains.


When you decide to give your car pressure, the pipe that transports automatic transmission fluid is likely to blow because it has been exposed to high pressure for the first time at constant acceleration. When in urban traffic, the same pipes are not running optimally because of low pressure driving at 40km/hr or less. Some mechanical issues such as heating of the water pump will also come up.

The tyres will also not be spared. If they are not used to high speed at high temperatures, they can end up bursting or wearing out easily since they have been exposed to heat they are not used to. If the suspension is not used to the up and down stroke movement, the shocks may blow because they are not used to constant vibration, among other mechanical issues.

Do modern cars require highway driving?

Most modern engines use fuel injection, computerised engine controls and improved fuel types that help it run more easily by default. In fact, experts say, there are many cars with 180,000kms that have surprisingly clean interior components. That is because modern car engines are designed to keep up with modern driving habits, and that includes city driving.

If you are driving at least 15 to 20 minutes on a regular basis, you are most likely giving your engine enough of a workout. If you are constantly taking five-minute trips or less, you could cause corrosion in your exhaust system and moisture buildup.