Eyeing the used lubricant sample from an unhappy customer, Joseph Fotue of Total Cameroon was stunned. The customer had suffered the sudden failure of a diesel engine, and when the engine was dismantled for repair, it revealed a hard, black deposit clogging the crankcase and other parts.

It was so thick that we couldnt measure its viscosity, and even at 150 degrees it didnt flow, Fotue recalled. The black mess even resisted dissolving in a solvent. Was this an act of vandalism, the distressed customer demanded to know, or bad faith on the part of the lubricant supplier? How else to explain a liquid oil that became virtually solid in the hot engine?

Digging into the problem, Fotue came to realize that it is actually quite common in Africa. When people drain their engines, they see this sludge. The sludge is a thick substance which worsens as water, soot and contaminants build up in the engine. It can rapidly destroy the engine if not discovered in time, he warned, because it will block the filter and consequently lead to failure as moving parts are starved of lubrication.

Fotue, a field engineer with Total based in Douala, Cameroon, described Africas sludging phenomenon to the Society of Tribologists and Lubrication Engineers, whose yearly meeting drew 1,400 experts in friction, wear and lubrication to Minneapolis, Minnesota, U.S., in late May.

Depending on how far the engine sludge has progressed, he reported at the conference, it may appear tan, brown or black in color; early on, it may form a pale, gloppy deposit. You can see it on the underside of the cup when the engine cap is opened, said Fotue, who has 10 years of industry experience and is a member of the South African Institute of Tribologists. He is also an STLE Certified Lubrication Specialist, since 2012.

A Closer Look

With deeper investigation, Fotue was able to identify three factors linking the sludging cases. First is lubricant oxidation, he said, calling it the most important type of deterioration. The reaction of the lubricant with air and heat leads to viscosity increase and also the formation of acids, resin and varnish.

These tenacious decay products plug up filters and orifices and leave sticky deposits that restrict the movement of valves and other critical components. Engine wear particles, water, dust and other contaminants make the problem worse. He reminded attendees of the Arrhenius equation, which calculates the effect of temperature change on the rate of a reaction. For lubricants, Arrhenius law means that for roughly each 15 degrees the temperature rises, the rate of oxidation will double.

African drivers and mechanics typically see two types of sludge: smooth and brown in gasoline engines and hard, granular and black in hotter-running diesel engines.

Soot contamination is a second factor. Here, we see carbon products enter the crankcase along with exhaust blow-by gases that escape past the piston rings. This can lead to filter plugging, too, so you need a high level of dispersant additives to keep the soot in suspension at higher concentrations, he said. Low-dispersancy engine oils are the culprit here, abetted by long idling times and stop-and-go driving in heavy traffic. Together they exacerbate the problem and give the granular, black sludge more time to form.

Water, another contaminant that is introduced with blow-by gases or through damaged seals or a failed head gasket, is the third deadly link. Water in an engine should evaporate, but if the engine temperatures are kept low, like when drivers are stuck in traffic, it cannot get warm enough to drive off the moisture. Instead, the water condenses and mixes with the oil to create a mayonnaise-like emulsion. From there, its only a short while before oxidation products, soot, water, unburned fuel and other contaminants begin to coagulate and form sludge, he related.

Climate of Wear

Oxidation, soot and water are universal, of course, but Africa also has distinct conditions that give sludge a foothold: overcooled engines, grinding traffic and unsuitable lubricants.

I noticed that throughout our country there is zero snow, yet many engines operate cold. Why is that? Fotue wondered. The two big reasons are thermostat removal and stop-and-go driving.

Many mechanics in Cameroon and elsewhere on the continent will remove a faulty thermostat without replacing it, he said, because Africa is warm and many people including mechanics think the thermostat is not needed. But without a thermostat, it takes longer for the engine to reach the optimum operating temperature. And because there is no regulation of the engine by thermostat, if it does heat up the temperature suddenly drops again. Its almost impossible for the engine to reach and stay in the optimal temperature range.

Citing data on vehicle warranty claims, Fotue elaborated later for LubesnGreases. Cooling system failure is the number one reason for vehicle failure, he commented. It represents almost 22 percent of failures, more than engine damage (19 percent), electronic systems (19 percent), fuel circuits (15 percent) or transmissions (6 percent).

Consumers should use a fully formulated coolant to regulate engine temperature, but unfortunately, another common name of coolant is antifreeze, Fotue pointed out. People in Africa think that they dont need it because the [ambient] temperature is generally too high and it cannot freeze. They use water without additives and glycol. The consequence is overheating of the engine.

Another simple but misguided tactic for mechanics and do-it-yourselfers to stop engine overheating is to remove the thermostat altogether, which leads to overcooling and hence sludge… It is now as a rule to remove the thermostat, even when there isnt problem.

Old School Oils

Many African drivers also purchase unsuitable engine oils. Many lubricants sold on the streets are obsolete categories, showing API SA/CA, SB/CA and so on, said Fotue. These obsolete oils, which have not been recommended by auto manufacturers for 50 years or more, lack the detergents, dispersants and antioxidants of current API and ACEA engine oils. This, plus neglect of proper maintenance, allows sludge to form and grow unchecked. Buyers should beware.

By contrast, a modern lubricant that meets the APIs SM and SN categories for gasoline engines or API CJ-4 for diesels (or their European counterparts, the ACEA 2012 and 2016 Sequences) is generations ahead in quality. It is formulated to control soot thickening, wear, piston deposits, oxidative thickening and sludge, plus to boost fuel economy and safeguard the vehicles emissions system.

Modern oils undergo a battery of rigorous tests to demonstrate they are fit for service, Fotue said. These include high- and low-temperature viscosity checks (using ASTM test method D445), soot control (ASTM D5967), oxidation and nitration (ASTM E2412), the crackle test for water (ASTM D6304), color (ASTM D1500) and total base number, which indicates the fluids reserve of acid-neutralizing chemicals (ASTM D2896 or D974).

We see lots of poor maintenance, Fotue went on. As described above, some drivers just use water as their coolant, without adding any glycol to the radiator. They rarely check or top-off low oil levels. They postpone oil changes until a more convenient time, which never comes around.

One pernicious problem, he added, arises from Africas horrible traffic jams, which can keep engines idling for hours a day without turning the wheels. This means even drivers who faithfully replace their oil at 5,000-mile intervals may be waiting too long, because their engine is overworking and stressed even though the car is not racking up odometer miles.

Fotue said that education is the first line of defense against Africas engine sludge. Drivers should read their cars manual and check the condition of their oil and engine
fill cap each time they fuel up. Dont neglect your maintenance, he urged. Use good oil. Dont remove the thermostat. Consider the effects of traffic jams. And use a glycol coolant.