There are many additives on the market that promise to stop engine oil leaks. Engine oil is used to slow the wear on the pistons as they drive the crankshaft. Oil leaks can be a dangerous and expensive problem. Leaking oil interferes with the operation of other engine parts. If oil leaks into the transmission fluid or onto the drive belt, the entire system may need to be replaced. One of the first signs of an oil leak is an oil spot under the parked car.
Gasket Leak Additives
This is the most common form of oil leak additives. The valve, or header, gasket is a plastic or silicone gasket located at the top of the engine block. It forms a seal between the block and the head. Even using long lasting products, over time, heat and pressure cause the gasket to dry out and crack. Oil leaks from the top of the engine as it is pumped from the bottom of the block to the top of the pistons. Gasket additives are designed to adhere to the plastic or silicon and cause the material to swell slightly and reseal the header. This is a temporary fix. For long-term leak prevention, replace the head gasket.
These additives promise to coat the engine parts with high-temperature Teflon that not only plugs any potential leaks, but also protects the engine parts from wear. According to Techni-lube, these additives can't adhere to the engine parts because the engine just isn't hot enough. The temperature needed to fuse Teflon to metal would cause massive engine failure. The Teflon moves through the engine as the car runs, sticking to other bits of Teflon on the way. While it is possible that these little clumps may find their way blindly into a leak, far more of these clumps settle to the bottom of the engine creating sludge. Ultimately, sludge is forced into the pistons, causing damage and wear.
These additives, while not specifically designed to stop leaks, often promise to "heal" an older engine as it increases performance. These additives thin the weight of the oil, reducing oil pressure and, theoretically, preventing pressure leaks. The problem, according to both the website Car Bibles and the FTC, is that most of these products just don't work. Some of these additives are nothing more than mineral oil and food colouring. An automotive engine is designed to work under pressure. Reducing pressure doesn't make the engine more efficient. These products may put off a high-pressure leak, but can seriously damage an engine in the process.