LIQUID CONFUSION
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0 il is many things to many people. In the rarefied atmosphere of oil company research labs it is "liquid engineering". In the hi-tech world of the engine designers it is the lifeblood that their product depends on for a long and healthy life. But on the workshop managers' budget sheet it represents a whole range of expensive consumables. Many drivers simply want to find the cheapest brand they can lay their hands on because the dipstick has shrunk and no longer reaches far enough into the sump,
In fact, the system is logical and you don't need a degree in oil technology to understand it. Manufacturers specify the
grade and quality of oil that should go in their engines, gearboxes or driven axles. The major oil companies produce lubricants to meet these international standards but call them by brand names. So when a driver opens his vehicle handbook he only sees lists of oil specifications and grades but only sees brand names when he wants to buy oil, so who can blame him for picking the cheapest.
Defining the correct oil starts with the engine, gearbox or axle manufacturer whose only concern is the quality and grade of oil used. From the design and testing of a driveline component before it is put into production the manufacturer will know the demands it will make on the oil. That allows him to draw up an oil specification, which is basically the degree of protection needed from the various additives.
Modem oils are complex blends of base oil and additives which are defined by their viscosity (thickness) and the quality standard they meet (API, CCMC and so on).
Viscosity modifier
Usually the first additive is a viscosity modifier which turns a mono grade into a multigrade. As an oil gets hot it gets thinner, so one that gives adequate engine protection when cold may not do so when hot. Conversely, an oil which gives good protection when hot may be like treacle when cold, making winter starting difficulu The viscosity improver allows the oil to take on a dual personality. For example, a 15W/40 oil is designed to act like a thin straight 15 when cold, but it has the characteristics of a straight 40 when hot.
Many engine manufacturers are particularly concerned with bore polishing when the high points of a freshly honed cylinder bore are 'bent over' into the valleys creating a smooth surface. In this process the metal is work-hardened, making it repel oil. This effectively leaves the piston running without lubrication so wear rates are greatly increased, oil consumption rises rapidly and total engine failure may not be long in coming.
Generally, the likelihood of bore polishing is increased by extending drain periods. To overcome this problem, the oil compa
nies put extra dispersant in the additive pack, which holds soot and other contaminants in suspension within the oil.
To make life more complicated a high level dispersant can actually cause bore polishing in new engines, so many trucks leave the assembly lines with a special 'running-in' oil in the crankcase. The engine is left to bed in for, say, 2000km before its first dose of high dispersant oils.
IDI diesels are particularly sensitive to the correct oil, says BP's John Hillier. They tend to dump more rubbish in the oil than Dls, so the oil must contain a high level of a dispersant additive. If not, it is possible for the oil to become thicker and thicker until it becomes like non-drip paint. While it is being mashed around by the engine all is well, but once the engine has stopped and cooled the oil can thicken into a gel. When the engine is restarted the oil pump cannot suck up this gel and the engine comes to a quick and expensive end.
Oils with high or low levels of dispersant still carry the familiar grade figures, such as 15W/40. Likewise, some gear oils have more EP (extreme pressure) additives than others, but have the same viscosity grade, such as SAE 80 or 90.
Synchromesh gears
On the subject of EP oils, while a high EP oil is essential to protect hypoid gears in a rear axle, it could min the synchromesh hubs in a gearbox designed for non or low EP oils, and vice versa.
That's why the major oil companies have large R&D centres where additive packs are carefully formulated and tested to ensure they meet the relevant specification. This costs a lot of money, which must be recouped somewhere — usually in the price of the product. Volume for volume typical additive packs cost around five times as much as the base oil. Skimping here could certainly reduce the cost of the end product, but that saving could have a dramatic effect on your driveline's service life.
So this is the situation: driveline manufacturers specify performance requirements for oils; oil companies work to a set of international standards but call their lubricants by brand names; and the potential cost of choosing the wrong oil is horrendous. So how do you find the correct oil specifications for your fleet, and which brands of oil meet those specifications?
Fortunately help is at hand. For a start if you run a large workshop oil company reps will call and they will be only too pleased to advise you. But beware — using an unnecessarily high grade of oil can waste as much money as repairing a vehicle after using too low a grade, so make sure you get several quotes.
Al] the leading oil companies publish charts or booklets listing the drive trains in all the various vehicles and showing which of their branded products meets the specification and viscosity requirements laid down by the respective manufacturers.
Much of this work is carried out by an independent Swindon-based company called Oats. It examines each vehicle's lubrication requirements and matches them with the specification of each oil companies' products.
Owner drivers
This is fine for fleets dealing directly with the oil companies, but drivers out on the road, and owner-drivers handling their own oil changes also have access to the relevant information in the drivers' handbook.
This will normally include the viscosity and specification of the oils required, so when buying oil simply look for that specification (and viscosity) on the packaging.
Unfortunately, there are exceptions, most notably from Mercedes-Benz but MAN, Volvo and Renault also specify oils using their own system.
Mercedes-Benz uses a sheet number system lo define its specification, but these numbers will not always be found on an oil company's packaging. This is a pity as Mercedes-Benz tends to set the pace on oil specifications, but much of its good work is undone by the lack of a tie-in with oil company packaging. Only your local MercedesBenz dealer or an oil company can decipher M-B oil specs and convert them into brand names.
At a roadside garage it may not always be possible to find a particular specification of oil. When topping up with a small quantity in a large sump no harm will be done. If owner-drivers want to handle their own oil changes then using the correct oils becomes critical, but there is time to search out the right one.
It is clear that using the right oil in a vehicle is crucial to its long term performance. In recent years the demands placed on oils used to protect the new generations of truck engines have risen in line with power outputs. Extending drain periods also adds greatly to the strain put on oils.
Emission testing
The other consideration is emissions testing. All engines bum some oil which adds to emissions, so it makes sense to use the specified oil to minimise this. In future this could make the difference between passing and failing the annual test, and as emission legislation tightens over the years it is likely that the frequency of engine reconditioning will increase.
Furthermore by using the correct specification of oil throughout a vehicle's life wear rates will be held to at a minimum. Less wear means lower oil consumption which in turn reduces emissions.
Engine designers are now talking of the day when oil consumption will have to be virtually eliminated if emission limits are to be met. Should that happen using the wrong oil could in theory result in an engine rebuild each year simply to get through the test.