In a word: Don't There is very little that any additional additive can do to engine oil and be compatible with all types. I have read a lot about a couple of them and it has been discussed frequently on the SDML. Also, the price of the more "advanced" additives makes buying pure synthetic oil cheaper than buying conventional oil plus additives. The more popular Slick 50 is a cheap base oil that has little bits of solid Teflon added. The fact is that engine oil needs to get into very tight spaces to lubricate properly, and if heavy engine oils have a hard time, imagine how well solids can get in. Basically they do nothing and end up getting filtered out by the oil filter as the filter becomes dirtier. So for about $25, you get a quart of cheap oil and a bunch of particles that really belong on a non-stick frying pan. Dupont (the manufacturer of Teflon) does not recommend Teflon for use in internal combustion engines, so why are people putting it in there? The latest additive is Prolong. It appears that Prolong is some sort of chlorine-based chemical with buffers to suppress chlorine's corrosive tendencies. Details about this stuff are still sketchy, but it won't be going into my engine until I see real racers using it. If you are a Prolong believer and don't mind spending $30 on it, it doesn't seem to cause problems as far as I know. There are various others, such as Duralube and STP. There has never been any conclusive evidence that any additives have any effect on engine wear at all. Some may even cause damage. Don't listen to the vendor's own tests or those stupid infomercials, because they are simply not true. The "running the engine without oil" test is nonsense. All modern engines require some oil pressure to keep the lash adjusters pumped up. It's simple physics. There is no way that an engine can run quieter with no oil after any kind of treatment (ala Prolong's infomercial). Even if the treatment has some magical properties, the lash adjusters require pressure to keep the valvetrain quiet! The million-mile test is also nonsense. These tests leave the engine running constantly. Almost all engine wear occurs when the engine is started, not while it is running at operating temperature.
What the additive manufacturers tell you is true - when you start your engine, there really is very little oil in the right place - most of it is in the sump. There is another alternative. I found a site called AutoEngineLube.com and they seem to be offering an interesting alternative. They have a system which uses a cylinder of pressurised oil and a solenoid valve, all connected to the regular oil system. It works with only one moving part, (the solenoid valve - duh!). When the key is turned on it opens the valve and the oil that was trapped in the tank the previous time it was running goes back into the oil gallery in 1 or 2 seconds and the low oil pressure light will flash off. There's likely to still be a little lag before full-on lubrication gets to the main bearings, but from what I can tell, this system will massively reduce that lag compared to starting from cold - it pressurises the system before the starter engages. Of course an engine that has set up for a few months and is completely dry will take a few more seconds. When the engine is turned off the solenoid valve shuts off in 30 milliseconds so you end up with pressure on the tank equal to the pressure the last time it was running. The tank will hold more than enough oil to accomplish this. Its completely over engineered as the tank is rated for over a thousand pounds and the hose is good for 300lb. Because the valve is designed for an industrial application with an expected duty life of several million cycles, AutoEngineLube give it a lifetime warranty. It only uses previously filtered oil from the gallery so no damage can be done by it in any way. Their system comes as a kit and requires some menial installation - most savvy home mechanics should be able to do it. I'm not sure how it would affect the warranty on a car engine. In theory, if it works, it ought to make no difference but you know what manufacturers are like - if you even sneeze on your engine, it's likely to void the warranty. Pop over and check them out if you're interested. If you end up buying one of these, I'd like to know what sort of results you get so I can add an objective review to my site. AutoEngineLube.com can be found here.
Your warranty should not be affected by installing the AutoEngineLube kit. According to the MAGNUSON-MOSS WARRANTY ACT OF 1975 installing aftermarket equipment does not void a vehicle manufacturer's original warranty.