Choosing the best engine oil for your car is very critical for its reliability and a long engine life. Given the number of engine oil manufacturers and the various grades & types available in our Indian Market, it is a difficult task to choose what is best and what shouldn’t be used in your vehicle. The easiest and the safest option is to stick to your manufacturer specifications given in your Vehicle Owners Manual. There will be a couple of specifications mentioned in your owners manual that you should know while choosing the right lubricant.
Understanding the Oil Specification for your Vehicle
Manufacturer will generally specify a minimum of two values for your Engine Oil specification. One will be the SAE Viscosity grading and the other will be the API/ACEA service classification. Both the values are equally important and the oil you select should match both the values or should be a higher rated product. Now lets understand the specifications so that you can choose the correct or even a better product for your vehicle.
SAE Viscosity Grading (eg. 15W-40, 0W-40, 5W-30)
The SAE Viscosity grading will be specified as xxW-yy. For eg. 15W-40, 5W-30. The most important value in xxW-yy is the last set of digits which specify the Viscosity grading of the engine oil at 100 degrees Celsius while the value xx in xxW-yy refers to the Viscosity grading at low temperature. For majority of climatic conditions in India, the xxW or the Winter viscosity rating is insignificant, but you can always go for an oil with lower xxW rating than your manufacturer recommended rating to get a better cold start performance.
The most significant value here is yy in xxW-yy. yy is the Viscosity Grading of the oil at 100 degree Celsius. Since the oil temperature of your car engine hovers around 100 degree Celsius at its optimum running conditions, the viscosity at this temperature is what determines the required specification of the oil. So if your manufacturer has recommended 20W-40 for your car, you should always stick to xxW-40. However, you can go for a lower winter rated oil like 10W-40 or even 0W-40 which will provide the best protection during cold cranking as well as normal running.
For better understanding, lets take the case of First Generation Maruti Suzuki Swift Petrol, which according to the owners manual recommends API SF 20W-40 (We will discuss the API SF part later). You should always choose 20W-40 and as an upgrade you can choose 15W-40 or 10W-40 to get a better protection during cold cranking. You can also go for premium Synthetic engine oils rated at 0W-40 which will provide the best protection and performance for your engine. As long as you use a 40 grade oil with the recommended or a lower W rating, your engine will be safe at all operating temperatures.
API Service Classification (eg. SL, SM, SN, CI, CJ, CK etc)
After choosing the correct SAE Viscosity grading, next you need to look at the API/ACEA performance rating required for your car engine oil. API stands for American Petroleum Institute while its European counter part is ACEA (European Automobile Manufacturers Association). The API rating is generally specified as API SJ, SM, SN etc for petrol vehicles and API CF, CH, CI etc for Diesel vehicles. The API service classification determines the type and contents in your Engine oil like the additives, detergents etc and API ratings always follows the Sx/Cx format where S stands for Petrol Oils and C stands for Diesel. The x part in Sx/Cx ratings follows the alphabetical sequence starting from SA, SB, SC….. to SN (as of 2017) and CA, CB ….. CK (as of 2017). The higher the x in Sx/Cx rating, that means the oil meets the latest generation requirements. Also the x rating in Sx/Cx is backward compatible for most vehicles. As of 2017, SN and CK is the latest rating while next year we may start seeing SO and CL rating further down the line SP, CM etc.
Just like SAE Viscosity Grading, API classification is also very important and should always match or should be an upgrade to the rating specified in your owners manual. The API SN classification for petrol engine oils are designed with protection for Turbo Charger, Ethanol Blended Petrol compatibility etc. So, if your Owners manual recommends API SL rated oil for your car, using the older SJ or SG rated oil can damage your engine. But you can safely use API SM or API SN rated oil for your car since SN is higher/latest on the alphabetical scale while SL, SJ etc are lower on the alphabetical scale compared to SM. The same is the case for diesel engine oils which will have a Cx rating. CA being the oldest and CK being the latest. So, if your owners manual recommends CH (CH-4) you can safely use CH, CI, CJ or CK but you cannot use CG, CF, CE since they are of lower grade.
ACEA, JASO and other Service Classifications
Apart from API, you might also see rating from ACEA (European Automobile Manufacturers Association), JASO (Japanese Automotive Standards Organization) and other OEM specifications such as VW, Fiat etc. These ratings are similar to API classifications but will have minor variations. For most European car manufacturers, they may not specify the API rating instead specify the ACEA rating. Similar to API, ACEA ratings are sequential starting with A1 to A5 for petrol engine oils and B1 to B5 for the Diesel engines where A1/B1 being the oldest and A5/B5 being the latest. In another year or two, we will see A6/B6 ACEA ratings. But unlike API rating, you cannot blindly for a higher ACEA rated oil without proper consultation. For eg, an engine designed for A3 rated oil may not be compatible with A5 rated oil but as long as you stick to correct SAE and API rating, your engine will be safe.