Oil on troubled motors

Here are some frequently asked questions about the mysterious fluid which you pour through an engine’s oil filler opening. What is the distinction between mineral and synthetic oils, and are there different kinds of synthetic oils ? Mineral oil is produced from base oils which in turn are derived from suitable crude oil. Base oils can be chemically treated to remove unwanted compounds occurring naturally in crude oil, like sulphur and aromatic compounds. Depending on how much refining has gone into the base oils, you get a range of mineral oils, all bolstered with additive packs. Synthetic oil, on the other hand, is produced in one of two ways: the first is to subject the purest base oils to molecular manipulation in additional chemical processes. This is sometimes referred to as synthetic technology. The second is to use a fully manmade liquid, either an organic polymer or an ester, as a base. Such a base, created in a laboratory is manufactured in a chemical plant. Mobil 1 was an early example of the latter type of synthetic oil. Castrol followed the super-refined crude oil route and called their oil synthetic as well. This led to a fierce debate about the meaning of the term “synthetic”, culminating in a clash between Mobil and Castrol before an advertising authority in 1999. The authority declined Mobil’s stricter definition of “synthetic”, a ruling that has led to the position where the marketers are having a field day with so-called synthetic oils, and consumers are left in the dark about which route was followed to produce any particular oil. In the oil industry, unfortunately, product formulations are closely guarded secrets of the big oil companies “for competitive reasons”. Why does engine oil turn a darker colour in use? The repeated heating/cooling to which oil is subjected in an engine naturally darkens the oil. Oxidation, which can be retarded by additives in the oil’s additive pack, but never completely stopped, also darkens the oil, just as oxygen causes a cut apple to turn brown. Such processes will cause the oil to become amber or brown in colour, but it will remain transparent. Soot, on the other hand, will cause the oil to become black (non-transparent). Soot, produced during incomplete combustion, is associated with diesel engines but can be formed in petrol engines, especially directinjection engines. Soot particles are typically small enough to pass through the oil filter and so they accumulate in the oil, thanks to the oil’s detergent and dispersant properties. Fortunately these particles are so small (try to imagine oneseventieth of a human hair!) that they don’t cause engine wear. Thus, engine oil that has turned dark or even black isn’t necessarily an indication that the oil is due for replacement. Can oil become diluted with fuel ? Yes, petrol and diesel fuel can find its way into the crankcase and dilute the oil. This is sometimes indicated by a gradual rise in the oil level on the dipstick. Causes include dirty or leaking fuel injectors, excessive idle time, frequent short-trip driving with resulting low engine temperatures, and worn piston rings or cylinder bores. Direct-injection petrol engines seem to be particularly prone to this problem. Fuel dilution exceeding 2.5% in petrol engines and 3.5% in diesels can create problems like reduced viscosity, increased volatility and accelerated oxidation. One antidote to fuel dilution is to adjust your driving pattern if possible to include occasional fast runs on the freeway to get the engine warm enough to evaporate the accumulated fuel in the oil. By the same token, if you go on the first long trip after having used the car for town driving, you sometimes find the oil level drops over the first 200km. What do motor manufacturers mean by “severe duty” for which shorter oil drain intervals are prescribed ? Many owners assume that because they use their car in a normal, everyday sort of way, the “normal duty” maintenance schedule applies to them. This may be a mistake. Severe duty include the following: Hot weather driving in prolonged stopand-go traffic; A predominance of trips of under 8km; Regular towing of a trailer, boat or caravan; Frequent driving on gravel roads. In addition, any engine past its prime should be regarded as performing severe duty. Once oil consumption starts to rise and power begins to taper off, the engine has to cope with a host of problems which newer engines do not experience. In the years before the veteran is wheeled into the operating theatre, it needs all the help it can get.