There are no hard and fast rules for curing an engine of sludge build-up. If its really bad, flushing the engine might be the only cure, but that could also cause even more problems. If flushing the engine results in bits of sludge getting lodged where they can do more damage, youre actually worse off. Its interesting to note that some race techs have reported sludge build-up in race engines as a result of aftermarket additives being used in conjunction with the regular oil. The chemical composition of the additives isnt as neutral as some companies would lead us to believe, and combined with particular types of oil and high-stress driving, they can cause oil breakdown and sludge to appear. The best lesson from this is dont use additives. When its an oil and water emulsion from a leaking or blown head gasket. If this happens, you get a whitish cream coloured sludge on the inside of the oil filler cap. Its typically cooler than the rest of the cam case and so the oil/water mix tends to condense there. If it off and the underside of it looks like its covered in vanilla yoghurt or mayonnaise, youve got a blown head gasket. A sure fire way to confirm this is if your oil level is going up and your coolant level is going down. The coolant is getting through the breaks in the head gasket and mixing with the oil. When it gets to the sump it separates out and the oil floats on top. A slightly more accurate way to check for this condition is to use a combustion leak tester, or block tester. There is one other possible cause for the mayonnaise like substance: a blocked scavenger hose. Most engines have a hose that comes off the cam cover and returns to the engine block somewhere via a vacuum line. This is the scavenger hose that scavenges oil vapour and gasses that build up in the cam cover. If its blocked you can end up with a build-up of condensation inside the cam cover, which can manifest itself as the yellow gloop inside the filler cap. Mineral oils are based on oil that comes from dear old Mother Earth which has been refined. Synthetic oils are entirely concocted by chemists wearing white lab coats in oil company laboratories. The only other type is semi-synthetic, sometimes called premium, which is a blend of the two. It is safe to mix the different types, but its wiser to switch completely to a new type rather than mixing. Synthetic Oils, despite their name, most synthetic derived motor oils (ie Mobil 1, Castrol Formula RS etc) are actually derived from mineral oils - they are mostly Poly-alphaolifins and these come from the purest part of the mineral oil refraction process, the gas. These bases are pretty stable, and by stable I mean less likely to react adversely with other compounds. They tend not to contain reactive carbon atoms for this reason. Reactive carbon has a tendency to combine with oxygen creating an acid. (As you can imagine, in an oil this would be A Bad Thing.) They also have high viscosity indices and high temperature oxidative stability. Typically a small amount of diester synthetic (a compound containing two ester groups) is added to counteract seal swell too. Pure synthetic oils are the types used almost exclusively within the industrial sector in polyglycol gearbox oils for heavily loaded gearboxes. These are typically concocted by even more intelligent who break apart the molecules that make up a variety of substances, like vegetable and animal oils, and then recombine the individual atoms that make up those molecules to build new, synthetic molecules. This process allows the chemists to actually fine tune the molecules as they build them. Polyglycols dont mix with normal mineral oils. This is the question most people whove just bought a used vehicle and are wanting to start their history with the car on fresh oil. Generally speaking, not any more. The engine must be in good working order and not be leaking right now. If thats the case, most modern oils are fully compatible with the elastomeric materials that engine seals are made from, and you shouldnt have any issues with leaks. motoringcorner@live.co.uk
