Low mileage Vs High mileage car
Many people only consider buying a car because it has low Kilometers. But is a low Kilometer car better than a high Kilometer car ? Well, if you are considering buying a 1-2 year old car, then a low Kilometer car would be a good choice. But if you are considering buying an older car, ask for a professional opinion. A low Kilometer car is not always a better choice over the same car, model and age that has higher Kilometers. Low Km cars are usually driven at low speeds for short distances and periods of time. Those driving condition will harm the engine more then driving the car at high speeds for long distances.
One Km of city driving will wear the engine a same amount as driving the car three Kms on the Highway.
Without entering into the engine/transmission science, lets consider only one main factor that will determine the life of the engine: lubrication. Assuming that a low Km car gets all the services on time, there are two problems that no service can avoid.
The air/fuel mixture that enters into the engine never completely burns. In "stop and go" driving the engine will use more fuel and as a result, more HC (unburned gasoline) will be concentrated inside the crankcase (the bottom part of the engine). The unburned fuel dilutes the engine's oil. Diluted oil will not lubricate the engine properly resulting in excessive wear.
Besides the unburned fuel inside the crankcase, moisture enters as well. This moisture, if not removed, will condense and will react with the oil to form sludge. Sludge, if allowed to circulate inside the engine will lower the efficiency of the lubrication system and will accelerate wear of the entire engine. See the photos below taken from an engine of a Volvo that has been driven around 9,000 km per year, (2006 MY, mileage around 110000 km).
One shows the engine oil pump removed from this engine and the other one shows the clogged oil pump pick-up screen.
These phenomena are results of extended oil change intervals, low quality of oil/filter used and short trip drives.
Most Volvo engines are equipped with a fixed orifice tube Positive Crankcase Ventilation (PCV) system to help remove the unburned fuel and moisture from the crankcase by drawing and sending them into the intake manifold. Here’s the problem, the engine lubrication and the PCV system will work poorly in all conditions that a low KM car is usually driven in. In many cases we have seen that the replacement of the PCV - Oil separator unit will not solve the issue. To perform a proper PCV system replacement and service the engine oil pan must be removed. This is the only way of cleaning the bottom part of PCV system. To have an idea about how much sludge can be accumulated inside the PCV system see the videos below.
Sludge inside the oil pump. Click to enlarge the photo.
Clogged pick-up screen. Click to enlarge the photo.