With diesel being a cheaper fuel, more buyers are now opting for diesel cars than petrol cars. But there are also concerns about maintenance and longevity of diesel engines, given that many of these buyers are getting a diesel car for the first time.
CarToq takes a look at the lifespan and maintenance of a diesel engine compared to a petrol engine, which should put the concerns of some of these buyers at rest.
Lifespan of a diesel engine
Most modern passenger cars in India use common-rail diesel engines. These are all direct injection diesel engines with an electronic control unit monitoring the engine parameters and controlling fuel flow through electrically activated fuel injectors. Diesel engines operate at high compression ratios as the heat generated from compressing air in the cylinders is what ignites the diesel fuel, unlike a petrol engine that uses lower compression and a spark plug.
It’s because of this high compression, that diesel engines need to be a lot stronger than a similar capacity petrol engine. This makes them heavier as well. The cylinder walls, the crankshaft, piston head, connecting rods all need to be stronger and thicker than what would be used for a petrol engine. Also read: Reducing noise levels in diesel cars
Since they are heavier, diesel engines are also low-revving engines, and don’t rev as high as a similar capacity petrol engine. This means they generate less friction in comparison. Also diesel fuel itself is slightly oily in nature and provides some lubrication to the cylinder walls and piston rings, better than a petrol engine would – as petrol is a drier fuel.
In India, it’s common to see Toyota Innovas, Mahindra Scorpios, Boleros and some older Toyota Qualis with over 400,000 km on the odometer. You will find drivers of these vehicles swearing that they have never had to open the engine for anything other than routine oil changes. With petrol cars, you’ll find that once a car reaches about 200,000 km, it will begin to knock a little, as the rings loosen up. It’s at this stage that it probably needs an overhaul. Of course, this depends a lot on how the vehicle has been driven – a well maintained and carefully driven petrol car also can last much longer.
But typically, diesel engines have nearly twice the life-span of a petrol engine if routine maintenance is followed. This maintenance, however, can be slightly more expensive than a comparable petrol. If you maintain a diesel engine well and drive carefully, it can last 400,000 km before needing a major engine overhaul.
Diesel engine maintenance
Diesel engines tend to dirty up their engine oil with soot much faster than a petrol engine. Typical oil changes for a diesel engine or a petrol engine average about 10,000 km between changes. Oil charges and filter charges are similar for both petrol and diesel engines. Where maintenance charges differ is with the fuel filter cost. A diesel fuel filter typically costs nearly 10 times more than what a petrol filter costs. Petrol filters are as low as Rs. 200 a filter, while a diesel filter costs as much as Rs. 2000 upward, depending on the car. This needs to be replaced every 20,000 km. Also read: Maintaining a diesel car
Engine mounts are another area of concern with diesel engines. Diesel engines tend to vibrate a lot and need effective damping. This puts a lot of stress on engine mounts. Mounts need to be inspected every 40,000-50,000 km and replaced if necessary.
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