When I checked the engine-oil dipstick of my car recently, I discovered the level was about halfway between minimum and maximum. It has not been long since its last servicing. Meanwhile, I have seen no signs to suggest the car may be losing oil. What are the reasons for a depleting oil level and what are the symptoms of oil loss?
The first thing to check is if there are any signs of oil on the floor where you park. Leaks are not common, but sometimes, a worn engine-oil seal or a drain plug that has not been tightened with a new washer can be reasons for oil dripping from the engine. Such leaks will be obvious especially if the car is parked overnight.
A more complicated cause of oil loss is worn piston rings. Initially, small quantities of oil will seep past the rings and combust with the fuel and air, but not show up at the exhaust pipe. However, the oil level will definitely drop. Over time, the piston rings wear down more, until you eventually see smoke spewing out of the exhaust. Bluish smoke is a clear indication that the engine's piston rings are worn and need replacing.
If you suspect the piston rings are worn, the best diagnosis is a compression test, which almost any workshop would be able to perform.
Another cause of blue exhaust smoke is weak valve stem seals. Usually, this will show up as a puff of blue smoke when you start the engine. Renewing valve seals involves the mechanic removing the engine cylinder to access the seals. But piston- ring replacement requires an engine overhaul, which is costlier.
Generally, some amount of oil consumption is normal, especially with engines that have clocked more than 80,000km. In such a case, 100ml to 300ml of top-up oil is necessary between service intervals.
Make sure you are always using the recommended grade of oil and only good and known brands. Cheaper alternatives are best avoided.