With regular 5,000 miles oil change intervals you should be just fine. When I check the dipstick (weekly - Saturday morning, first thing - cold engine) I look for oil level and condition. You can observe the oil gradually darkening over time. It is supposed to do that because there are detergent additives to hold contaminants in suspension. The only way sludge can develop is when the oil is overwhelmed by contaminants that no longer stay in suspension and drain out with the used oil. So if you check and change the oil regularly, there is no problem. If you chose to switch to synthetic oil, like Mobil 1, then you are super protected. ========= copied from someone else:
*Just what is synthetic oil*? Technically speaking, synthetic lubricants are made by chemically combining, in a laboratory, lower-molecular-weight materials to produce a finished product with planned and predictable properties. Don't be confused by this technical double-talk. What this means is that synthetics are custom-designed products in which each phase of their molecular construction is programmed to produce what may be called "the ideal lubricant." This process departs significantly from that of petroleum lubricants, whose physical components, both desirable and undesirable, are inherited from the crude oil from which they are refined. Crude oil possesses thousands of varieties of contaminants, depending upon the oil's geographical and geological origins, which no amount of refining can entirely remove. Corrosive acids, paraffins and other waxes, heavy metals, asphalt, naphthenes and benzenes, as well as countless compounds of sulfur, chlorine, and nitrogen, remain in the finished product. Equally as important, petroleum oil molecules, as contrasted to uniform-sized synthetic oil molecules, vary significantly in size, shape, and length. When your engine heats up, the smaller molecules evaporate, while the larger ones tend to oxidize and become engine deposits. As a result, refined petroleum lubricating products differ widely in their overall quality and performance. The presence of and the resulting drawbacks of the undesirable constituent elements lie at the very root of the considerable performance differences between synthetic and petroleum-based motor oils. Contrary to what many may believe, synthetic lubricants are not a recent development. As early as the 1930s, Standard Oil of Indiana conducted research into synthetic oil. More serious development and production was commenced by the Germans during WWII, as their conventional lubricants congealed and froze on the Eastern front and stalled their advances into the Soviet Union. As jet engines were developed after the war, it soon became evident that conventional lubricating oils couldn't withstand the high temperatures and pressures, and synthetics came to be used in all military commercial jet aircraft engines. Then in the
1960s history repeated itself, and it was again cold weather that spurred further development work as the U.S. Army needed better lubricants for Arctic and Antarctic use. Still later, NASA specified synthetic-based lubes for all space vehicles, including the Space Shuttle. Today's automotive synthetic lubricants have evolved as an almost direct result of these demanding military and extraterrestrial lubrication requirements. The U.S. Department of Energy lists no fewer than
*sixteen* performance parameters for any modern automotive motor oil. These are:
-Low temperature fluidity (low pour point)
-Low volatility...i.e. resistance to evaporation and resultant oil thickening...good oil economy, additional engine protection
-High temperature oxidation resistance (of the oil itself)
-Lubricity...the oil's slipperiness
-Thermal stability...resistance to performance loss due to temperature change
-Compatibility with engine metals, elastomers (i.e. "rubber" seals), oil filter elements, paints, and finishes
-Wear protection and film strength
-Freedom from deposit formation...good dispersant and detergent characteristics
-Compatibility with other engine oils and additive packages
-Extended drain capability
-Water stability...propensity to remain separate of water molecules
-Corollary effects on an engine's octane requirements
-Ambient-startup protection...ability to protect against oil starvation during initial startup
-Anti-rust properties
-Compatibility with catalytic emission control systems
-Compatibility with alcohol-containing fuels
Chief among the areas in which the pre-planned and predictable properties inherent in premium synthetic lubricants significantly surpass those of premium petroleum oils are: low temperature fluidity... and thus improved ambient startup protection; low volatility (higher boiling point...greater resistance to evaporation); high-temperature thermal stability; oxidation resistance; lubricity; fuel economy; film strength, and wear protection; extended drain capabilities; water stability; and high *natural* detergent characteristics (resulting in a cleaner engine with less additive content). synthetic oils are also renowned for their high-temperature thermal stability. Superior high-temp stability ensures and engine lubricant's capacity to protect vital engine components during very-high-temperature operation, such as hot summer driving, sustained high-speed driving, repetitious stop and go metropolitan driving, driving in mountainous terrain, pulling a trailer, or any driving with a small harder-working piston or rotary engine. Underhood temperatures also take a quantum leap with the use of power options, especially air conditioning, and because of emissions devices and emissions-related engine redesign. It is important to note that, even though the dash gauge may register only a 200F or so water/coolant temperature, the temperature of the sump and of all the assorted bearing surfaces significantly exceed the water temperature, and often surpass 500F on the piston ring and cylinder wall areas. These high-temperature surfaces serve to rapidly decompose petroleum oil and additives, as well as contribute to their shorter service life, while the synthetic is largely unaffected. Beyond the protection afforded an engine during these particular instances of high-operating temperatures, high-temp thermal stability moreover permits an engine oil to deliver overall extended service life (significantly longer drain intervals) in all driving conditions, because it prevents the phenomenon of sludge and carbon deposit formations on critical engine parts (valves, valve guides, oil channels, lifter assemblies, piston rings, et al.) due to oil thickening, a problem commonly attributable to petroleum oil breakdown at high temperature. As these deposits accumulate in the oil circulatory system, oil flow drops, thus accelerating engine wear. To the user of synthetics, the benefits are (1) reduced wear of critical engine components; (2) significantly reduced sludge and varnish... a cleaner engine; (3) reduced engine drag due to uniform viscosity; and (4) increased fuel economy due to reduced component wear. "Film strength" refers to the amount of pressure required to force out a film of oil from between two pieces of flat metal. The higher the film strength, the more protection is provided to such parts as piston rings, timing chain, cams, lifters, and rocker arms...wherever the lubricant is not under oil-system pressure. Synthetics routinely exhibit a nominal film strength of well over 3,000 psi, while petroleum oils average somewhat less than 500 psi. The result is more lubricant protection between moving parts with synthetics. The remarkable ability of synthetic oils to reduce internal operating temperatures is far too important to ignore, since high operating temperatures contribute directly to premature failure of mechanical components and gaskets and seals. Coolant (i.e. water/antifreeze) cools only the upper regions of an engine. The task of cooling the crankshaft, main and connecting rod bearings, the timing gear and chain, the camshaft and its bearings, and numerous other components must borne entirely by the oil. Popular Science article on synthetic oils, veteran race car driver Smokey Yunick was quoted: "When you disassemble an engine that's been run on petroleum oil, if you examine the rings and cylinder bores with a glass you'll see ridges and scratches--that's the wear going on. With polyol (a variety of synthetic), when you take the engine apart everything has the appearance of being chrome-plated. In the engine we ran at Indianapolis this year we used a polyol synthetic. When we tore the engine down, you could still see the original honing marks on the bearings...no wear at all. We put the same bearings back in because the crankshaft never touched the bearings. I've never seen that before."