The container that holds your engine oil underneath your car is made of very thin, sheet metal often aluminum. Because the bottom of the oil pan is so thin, the opening that technicians use to drain your oil cannot hold very many threads. The oil plug which is removed and replaced every time your oil is changed clings to those few threads. The reason for this is that manufacturers try to make your car as light as possible so that they can meet their fuel economy requirements (CAFE) and, of course, the less metal there is in a part the cheaper it is. It might sound unreasonable to think how little it would cost to have an oil pan that was just one-quarter inch thicker, but multiply this by tens of thousands of parts on a car and pretty soon you’re talking lots of weight and lots of money.
Depending on the make and model of your car, you can expect the threads to wear out on your oil pan as early as 40,000 miles just from normal wear and tear. It can be sooner or later than that depending on how often you change your oil. The problem is that when this happens, there’s not a “safe” solution to the problem other than replacing your entire oil pan. This can cost anywhere from $150 to $350 depending on the make and model. There are lots of less expensive solutions some suggest like oversized plugs, rubber plugs, and re-threading but they are not 100% effective. If you gamble with one of these and the rubber plugs pops out, you’re looking at buying a new engine for thousands of dollars. In modern engines you have only a few “seconds” to stop an engine that loses its oil which is exactly what happens when the plug drops out.
As if this isn’t enough to concern you, the technician who changes your oil can easily strip the threads in the oil pan by over-tightening the oil plug. When this happens, you probably won’t know about it until you change your oil again and maybe not for several oil changes. Stripping threads isn’t necessarily an “all or nothing” event. Over tightening the drain plug slightly, repeatedly will cause the thread to wear out prematurely.
Each manufacturer has a specification for exactly how tight the oil plug must be in the oil pan. It’s measured in foot-pounds of torque and a typical spec would be 18 FP. If the plug isn’t tightened enough, it might fall out. This sometimes motivates the technician to over tighten the plug just to be safe. If the plug is too loose and falls out, it could cost him his job. To be sure that the oil plug is tightened exactly right, the technician must use a torque wrench which shows the foot-pounds of torque that the plug has been tightened to.
Believe it or not, many technicians still don’t use toque wrenches. Without one they are just “guessing” how tight your oil plug is. This is a good reason for you to be very careful who changes your oil. Don’t be shy and specifically ask the service department who changes your oil if their technicians use torque wrenches. It wouldn’t be bad idea to find out the manufacturer’s specification for torquing your oil drain plug. It shouldn’t be necessary if you have your oil changed by the dealer, but it might if you use an independent service company or quick-lube company.
The person who changes your oil is the lowest paid individual in that service department. He’s called a “lube tech” and it’s generally considered a starting position for an auto technician. The turnover in this position is usually much greater than for regular mechanical technicians. I’m sure why you can understand why this puts you at risk for not having the job done right.
Be very leery of advertising promoting cheap oil changes. It’s fine to save money having your car serviced, but you should be sure that the person working on your car knows what he’s doing and uses the proper tools. He must know the manufacturer’s specifications for tightening your particular oil plug and he must use a torque wrench. Ideally, you should find a trustworthy, knowledgeable lube technician and always have him perform all of your oil changes. That way, if there’s ever a question about who over-torqued or under-torqued your oil plug, there’s only one person who can be held to blame.