Don't expect a miracle in a can

If you have been in an auto parts store, down an auto care isle, or watched infomercials then you have seen them. These are the miracle in a can products that promise to do almost magical things to your engine. There are some that claim they will make your engine last for ever, be cleaner, stop leaks, get better gas mileage and so on. The truth is these products produce varied results some work great while others do nothing to fix the problem. Most of the problems these products attempt to resolve could have been prevented by doing regular maintenance on your vehicle.

Stop Leak Products
These are probably the most common types of products out there within this group there are products that stop coolant leaks, oil leaks, and I would also include ones that stop burning of oil.With the various stop leak products you actually have a decent chance of them working. The bad news is that any fixes they provide are temporary at best. Oil stop leak products work by either "reconditioning" seals and gaskets or by thickening the oil so it doesn't leak out (this is also how the products that stop your car from burning oil work). With ones that recondition seals and gaskets all they do is cause the gaskets to swell so that the gasket plugs the gap, void, or crack. These will work for a while but eventually you will have a leak again. The only real fix is to replace the gasket or seal that is leaking. The products that thicken the oil I am not a big fan of as they really don't fix anything but just mask the problem. Add to that these products thicken oil I start to question if they are really good for your vehicle since you vehicle was designed to run with a specific weight of oil. As far a coolant stop leak products, I have had varied success with these, some of them seem to work some of them don't. Basically if you have a leak on a non moving part of your coolant system (i.e. not the water pump) then this product will plug the hole. I don't know how permanent these fixes are but once I have gotten home I go do a proper fix (solder, weld, or replace) so that I don't have to worry about the stop leak product.

Clean mechanical parts inside your car
These are also very common products and provide varying results. There are products to clean your fuel system, combustion chamber, engine, transmission, cooling system and so on. Basically these products are solvents. The ones that are put into the gas tank are meant to do one or more of the following:

1. Remove deposits from the fuel system. This usually called fuel deposits and are basically varnish. This can happen over time if you let vehicles sit for a while, the vehicle doesn't consume much fuel, or has a lot of miles on it. This also includes products like fuel injector cleaner or carburetor cleaner. Here I think that some products work better than others, but generally they won't cause any damage if used.
2. Remove water from the fuel. Products that do this usually have alcohol in them as alcohol will absorb the water and will still blend with gas. Getting water in your tank can happen if you have an old vehicle who's tank doesn't seal well, or if you bought some bad gas. These products were more common years ago, but now with most gasoline already having ethanol in it the need to remove water is lessened. These products usually work well as they solve only one problem that is pretty simple to fix.
3. Oil additives to clean out deposits in the engine. Personally I don't like these products as they thin the oil. This will decrease the ability of the oil to properly lubricate. I have used the products in the past but when I do I only use them just before an oil change and then only drive for a little bit with them. I only do it the first time I change oil on a vehicle because most people don't change their oil as frequently as they should and this will remove the deposits and sludge that have built up. If you change oil when you should this is something that never needs to be done. Using these products on a very neglected engine may actually make things worse as those deposits may have been plugging leaks or filling voids so now your vehicle may leak oil or burn it so it is best to just take care of your stuff to begin with than hope for a miracle fix in a can.
4. Coolant system cleaners. My feeling with these is similar to that of oil additives, they may work, but you would be better off taking care of the system to begin with than using one of these products and hoping for a miracle. Usually issues these products resolve are silted up cooling systems, rust, and calcium build up. These problems can all be avoided by doing a flush and fill on your coolant regularly. Also as with oil additives using one of these products may reveal other problems as they clean away the neglect. 

Performance improvements in a can

Unless you are running an extremely high compression engine or using a lot of boos don't expect much of anything from these products. The reason is that mostly these are placebo products. The only ones that do anything are those that increase the octane of the gas you are running, or in the case of diesels increase the cetane number. Increasing the octane doesn't do anything unless you have an engine designed for higher octane (even higher than the 91 or 92 premium fuel) than can normally be found. Unless you have modified your engine substantially (made a race engine out of it) you don't need these. Also don't expect any product to magically increase your fuel economy. If you use one of these products and your car magically starts running better it probably is because something is wrong with your car that needs to be fixed. It will be cheaper in the long run to actually fix the problem instead of keeping buying stuff in the can.

So what products do I like

There are some gems out there for the products in a can. Below is a list of products I like and have had success with in the past.

Oil stop leak - If you really want to use a product to stop oil leaks and not just replace gaskets or seals then go use something like Valvoline Max Life or Mobile 1 High Mileage. I would recommend either of these since you aren't playing backyard petrochemist. These are designed to meet the correct specifications of the oil for your vehicle instead of you just dumping stuff in. Don't expect results overnight with these products as it takes time for them to cause the seals and gaskets to swell and plug the gaps or cracks.

Coolant stop leak - I have had success in the past using the Bar's Leaks Lquid Aluminum product. When using products like this you need to drive the vehicle around for a while. This prevents it from solidifying into a big clump in the overflow tank. As I have mentioned I use this as a temporary fix and when I get home I go and do a real fix. 

Fuel system cleaners - Lots of people swear by Chevron Techron, but personally I like the Berryman B-12 Chemtool fuel system cleaner or injector cleaner. Basically these are some of the most caustic things I have ever used. I was introduced to them when cleaning the intake manifold on my car and had gone through several cans of regular carb cleaner and the guys at the auto parts store suggest the spray form. It really does clean well, don't get it on your paint, or on your hands. Also recently I have seen a couple of gas stations advertising the they carry gas to meets or exceeds top tier gas standards. I would say using these fuels would be a better option as again you aren't playing back yard petrochemist. Both Holiday and Kwik Trip in my area have recently started offering these. 

Oil additives for cleaning - I have used Seafoam to do this I put in the recommended amount and drive for a max of 30 miles and then change oil. I don't regularly use this since changing your oil at the correct time is the better option. As a side not Seafoam works great for fogging motors when putting them away for the season.

Coolent system cleaners - None, just do regular flush and fills.

Performance in a can - None, but if you really feel you need to run high octane fuel you can always go and get some leaded avgas down at the nearest airport for about $6 a gallon or race track for about $8 a gallon. If you feel you still need more octane then you are doing something wrong.