Eyeing the used lubricant sample from an unhappy customer, Joseph Fotue Sado of Total Cameroon was stunned. The customer had suffered the sudden failure of a diesel engine, and when the engine was torn down 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 engine?
Digging into the problem, Fotue came to realize that this problem 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 destroy the engine if not discovered in time, because it will block the filter and lead to failure.
Fotue, a field engineer with Total based in Douala, Cameroon, described Africas sludging phenomenon to the Society of Tribologists and Lubrication Engineers, which met last week in Minneapolis, Minnesota, United States.
Depending on how far the engine sludge has progressed, he said, it may appear tan, brown or black in color; early on, it may form a gloppy, mayonnaise-like 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.
With further investigation, he was able to identify three factors linking the sludging cases. First is lubricant oxidation, he said. The reaction of the lubricant with air and heat leads to viscosity increase and also the formation of acids. He reminded listeners of the Arrhenius equation regarding the temperature dependence of reaction rates: For lubricants, Arrhenius law means that for roughly each 15 degrees the temperature rises, the rate of oxidation will double. Thus, African drivers and mechanics 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, he continued. 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. Long idling times and stop-and-go driving in Africas heavy traffic exacerbates the problem, giving sludge more time to form.
The third common link is water. 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. So oxidation products, soot, water, unburned fuel and other contaminants begin to coagulate and form sludge, he explained.
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 pondered. 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 explained, 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.
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. This plus neglect of proper maintenance allows sludge to form and grow unchecked.
We see lots of poor maintenance, Fotue went on. Some drivers just use water as their coolant, without adding any glycol to the radiator. Low oil levels are rarely topped off. Oil changes are postponed 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 and stressed 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 even though the car is not racking up odometer miles.
In closing, Fotue believes that educating drivers is the first line of defense against Africas engine sludge: Dont neglect your maintenance. Use good oil. Dont remove the thermostat. Consider the effects of traffic jams. And use a glycol coolant.