The oil becomes thicker as the temperature reduces and becomes thinner as the temperature increases. The operating temperatures encountered by the engines are above 100°C, so the mono grade oil (i.e.) SAE 40, 50 etc performs its expected duty during the normal operating conditions. However during winter months especially in the early morning the mono grade oil becomes very thick and starts giving lot of resistance during starting of the engine. Multi-grade oils take care of the viscosity requirement of the normal operating engines, as it does not become too thick during cold temperatures and too thin with increase in temperature.. When oil does well at both extremes it gets a “multi-grade” rating that includes a number/letter followed by W and a number, such as 20W40.The viscosity changes with temperature will be very minimal in multi-grade oils, as multi-grade oils tend to be thinner at low temperatures and thicker at high temperatures than mono-grade oil.
The viscosity of the oil for any application depends on the speed, load, and the clearance between moving parts, type of lubrication and finally the ambient temperatures. Oil must provide protection over a wide range of temperatures from cold starts to long hauls. When oil does well at both extremes it gets a “multi-grade” rating that includes a number/letter followed by W and a number, such as 20W40. In a hot climate or driving through a region where a combination of high heat and high-altitude are encountered, the operation & maintenance manual provided by the manufacturer, will probably give suggestions for a multi-grade or “all-season” oil such as 15W-40. Such oil has the cold flow characteristics of 15-weight at start-up, yet the coating and protecting property of 40-weight oil at the high temperatures. In a predominantly cold climate, the recommended oil might be a 5W-30. However it is advisable to be guided as given in the operation & maintenance manual of that equipment.
In general, the functions of engine oil are as under:
Lubricant is a substance interposed between two surfaces in relative motion for the purpose of reducing the friction and wear between them. Lubricant provides a protective film which allows for two touching surfaces to be separated and "smoothed," thus lessening the friction between them and correspondingly less heat generation.
The benefits of multi-grade oil are as under: Multi-grade oil is thinner at low temperatures and as such the oil from the sump reaches all parts of the engine quicker than mono-grade oil as soon as the engine is started thus it reduces wear to that extent. Multi-grade oils enable better fuel economy than mono-grade oils. As multi-grade oils tend to be thinner at low temperatures and thicker at high temperatures than mono-grade oil it offers better protection to the engine. Thus it reduces oil consumption.
Higher quality engine oil is needed for turbo charged vehicles as they have better fuel combustion thereby increasing thermal load on engine oil and soot production is increased.
The performance levels of chemical properties relating to detergent action and dispersion in the two engine oils are different. Accordingly API service classes have two general classifications: S for gasoline engines and C for diesel engine. It is possible for an oil to conform to both the gasoline and diesel standards. (Note: Combined API Service Classification motor oils are highly effective at reducing and controlling sludge and varnish deposits, acid and foam formation and have improved oxidation stability. Most of the oils in the PALCO range meet such minimum levels and therefore possess the required standard and accordingly they are suitable for both petrol and diesel engines.)
The oil pressure may drop because the oil has thinned down considerably, due to fuel dilution. It could also be because of insufficient oil in the system, either because of an oil leakage or excessive oil consumption or even possible oil pump failure, causing the oil to not circulate. Check the oil level in the sump and also for fuel dilution. If both seem to be in order, check the vehicle for pump failure or any other mechanical problem.
The reasons for excessive oil consumption may be due to any of the following reasons:
One of the reasons can be overheating of the engine parts, due to little or no lubricant present in the system, resulting in friction which, causes micro welds in the engine, and ultimately leading to seizure of the engine. The seizure could also be caused by over thinning of the oil, due to fuel dilution. The major reason could also be operational problems and not the oil. Further if the engine becomes overheated due to any other reason viz. the cooling system not working properly or driving overloaded truck for a long period etc. the engine could still seize.
The performance enhancing additives of the oil viz. TBN, anti-wear, ant-oxidant etc. gets used up in service and below certain levels the oil will not be in a position to protect the engine. Oxidation of the oil beyond certain limits will start corroding the equipment or leave unwanted deposits on the moving parts. Further contamination of the oil with water, dust, dirt and soot from combustion products shall cause corrosion and abrasive wear. In view of these reasons that we need to change the oil once it looses its useful life to protect the engine.
The best way to judge whether the oil’s life is exhausted is to test a sample in the lab. If the TBN has decreased a lot from its starting value and/or the viscosity has increased or decreased substantially, the oil needs to be changed. Since it is not possible to test the oil in the field, it is suggested to look into the following warning signal:
Oil should be changed as per the equipment manufacturer’s recommendation after fixed hours of operation or after fixed kms. of running, provided the right quality of the oil is used as suggested by the equipment manufacturer. These change periods are established after extensive bench tests & field trials
The oil level should be checked with the vehicle on a level surface either before starting the engine, or at least two or three minutes after stopping the engine. If the vehicle is on a slope the oil level indication may be inaccurate. Pull out the oil dipstick, wipe off oil with a clean cloth, insert the dipstick all the way into the engine, and then remove it again. The oil on the stick should be between the upper and lower limits shown on the stick. If the oil level indication is near the lower limit add enough oil to rise to the upper limit. It is important to keep the engine oil at the correct level, to ensure proper lubrication of the vehicle's engine.
Engine oil should be drained out only when the engine is still warm. The engine oil temperature may be high enough to burn your fingers when the drain plug is loosened. Wait until the drain plug is cool enough to touch with your bare hands. Remove the oil filler cap and place a drain pan under the drain plug. Remove the drain plug and drain out the engine oil. After the oil has been drained out completely, tighten the drain plug and fill in the recommended grade of engine oil in correct quantity. Always change filter when changing engine oil.
The engine oil used in four stroke 2 wheelers/3 wheelers lubricates the engine, the wet clutch and the gears. It needs to take care of higher temperature operating condition since the engines are air-cooled unlike the passenger car engines which are cooled by water or by a Coolant. Further, it should have controlled friction characteristics to take care of the wet clutch requirement. Thus 4T oil fortified with special additives is required for 4 Stroke Motor Cycle Engines.
Two stroke motorcycle/scooter’s engine may either have a premix system or a separate oil injection system. In the former, lubricating oil is mixed while filling petrol in a particular proportion. In case of a separate oil injection system, the lube tank is simply filled as there is an in - built unit in the vehicle, which controls the flow of oil in petrol.
Two-Wheelers generally have a 2-stroke engine inside it, which works differently from a 4-stroke engine present in a car or truck. Truck and car engine oils contain additives, which results in higher deposits and smoke and that will lead to spark plug fouling if used in 2 wheelers. Further truck and car engine oils do not contain a solvent, which is required for a 2-stroke engine because it has to mix with petrol.
Improper combustion of bad quality/adulterated fuel causes abnormal increases in load on the engine which in turn affects the performance of engine oil. Further the by products of improper combustion, shall damage the composition of lubricant if by chance it goes into sump, thereby effecting the overall performance of engine oil.
Gear oils should also be changed at regular intervals as they are most prone to external contaminants like dust and water which results in gear wear. Recommended grade of gear oil must be used for proper lubrication of gears to prevent vehicle break down and avoid costly repair and maintenance.
Certain amount of oil separates from the grease depending on the operating conditions and also during rest periods or during storage. Excessive separation of oil from the grease during storage indicates that the grease has not been cooked well. Grease must be removed uniformly from all sides of the pack for application because any cavity formed shall results in the oil separating from the grease in the pack. Pack only half or a third of the bearing housing with grease as cramming the bearing housing with grease can result in overheating, leakage and a possible seizure due to the non-availability of adequate oil.
Open the brake fluid reservoir cap and look inside to determine the current level. If it is at the "full" mark, close the reservoir and if the fluid level is below the ""add" line, have your disc brakes checked and add or "top off" the fluid. If the fluid looks dark, it is time to have it changed. Mark the date of the inspection in your maintenance log. For safe driving inspect the brake fluid level periodically.
Good quality Coolants have the special rust preventive pigment which forms a coat over the inner part of the engine. If good Coolants are not used rusting, scaling & sludge formation takes place in the engine, which results in blocking the Coolants path thus overheating the engine & reducing the performance of the vehicle.