Motor Oil Myths and Facts

[El Calor]

History

As internal combustion engines for passenger vehicles have been forced to become more fuel efficient, less polluting, smaller, and longer lasting, their lubrication needs have changed dramatically. These changes in the engines have required the development of multi-weight detergent motor oils that are suitable for the tighter clearances, higher heat, and higher RPM of these engines. These oils have additives to reduce wear (especially at start-up), maintain viscosity, and to suspend the soot and contaminants (by-products of combustion) that they wash off the interior engine parts. A side benefit of these oil's ability to maintain viscosity and suspend soot is that the oil change intervals have become longer on most vehicles.

Sludge

The number one reason for oil changes is to prevent the formation of sludge. It's important to understand how sludge forms and how sludge formation is prevented.

How Sludge is Prevented

Additive in the detergent oils 'wash' any contaminant particles off of internal engine parts and hold these particles in suspension until the oil is changed. It's important to understand that these particles are too small to cause engine wear, but they do turn the oil a darker color. The key thing is to change the oil before the oil becomes too saturated with contaminants to hold any more, but color is not an indication of this condition.

How Sludge Forms

As explained above, modern detergent oils suspend contaminants so they do not settle on engine parts and form sludge. When the oil becomes saturated with contaminant particles new particles settle out of the oil onto the internal engine parts and form sludge. This is why it is so critical to perform oil changes before this level of contamination is reached. The only way to know if you're oil needs changing is to have an oil analysis done. Absent this, play it safe and follow the severe service interval specified in the owners manual. Remember that the contaminants come from the combustion process of the gasoline and and the air. Synthetic oil will not prevent these contaminants. Synthetics may be marginally better at suspending more contaminant particles, but not enough to prolong oil changes by much.
Never attempt to clean the inside of your engine with one of those engine flush procedures that many shops try to sell. If you've been diligent about oil changes there will be no sludge. If there is a lot of sludge then the last thing you want to do is to dislodge it all at once.

A good article about sludge can be found at: Toyota Sludge Article

Oil Change Intervals

Few subjects generate as much debate on Usenet as the proper oil change interval. Since few people bother with oil analysis the debate centers on time and mileage.

http://www.nordicgroup.us/oil.htm

[phillyb]

I'll partially disagree with the part about engine flushes. An engine flush is usually recommended whenever the oil hasn't been changed on time based on mileage OR time. I would recommend that as long as the oil changes are normally regular and the most recent oil change was overdue. Also, about every 15,000 miles (or every FIVE oil changes).
I'll agree not to use it in the case that the oil change history is unknown, and/or the engine has a lot of miles on it. Once regular oil changes are performed on the vehicle again (about five without going overdue), and you have verified that there is little to no oil consumption, an engine flush is perfectly fine to perform. An engine that is cleaner on the INSIDE will pollute less on the OUTSIDE. In most cases, if its cleaner on the inside, it also runs more efficiently. For the higher mileage engines, maybe use an oil that will also recondition seals and gaskets and prevent/reduce leaks, burning, and consumption.

Phil