Wow, how many things can be wrong in a single post?
Yes, detergents are required in gasloine, but that doesn't mean that even more than the minium required is enough. Some gasolines have more detergents than others. Mobil Super Premium for one. Also different brands of gasoline s use different detergents, some of which are more effective than others, ie Chevron Techron. ANd the advice I was quoting came from a petroluem engineer working for one of the big oil companies, about applying his knowledge to his personal car, a Corvette. HE says that each additive package actually makes its own form of deposits, rather than cleaning ALL deposits.
BTW the reson for running ofr a while then switching versus switching every tank, is that with every tank, you are now running a mixture of additive packages, that are both cleaning and adding deposits. And you are now in the realm of a petroleum test driver.
BMW DOES recoomend occasional use of gasoline additives over an above what is in teh gas. The even sel a BMW Fuel System additive/cleaner. In the Z3 world a LOT of people have had fule tank level snsors whack out with using premium gasoline by time itself over time. Occasionaly use of either BMW or Chevron fuel system addtive removes the deposit is from the fuel level sensor that causes the trouble.
Oxygenated fuels are NOT for reducing carbon. Oxygenated fuels came into being as an interim method to fool carbuerated cars into running leaning. The carb delivers the same amount of fuel, but since part of the fuel is oxygenate, you actually end up with a lean burn. With most of the cars now being fuel injection, oxygenates are not required, but the oil companies like them, since they reduce gas mileage (less burnable fuel) and increase the sale of gasoline. It is true that leaner burning reduces carbon by having more complete combustion.
Lead is only a lubricant for the valves, and saying lubricant is a misnomer. The lead actually acted as a cushion to the closing valves. This prevented damage to the soft valve seats used at the time. All later cars (built after about 1975) have hardened valve seats that do not rely on the lead to cushion the valves. The lead was not in there for the purose of cushioning, but since it was inthere to prevent detonation, it made the manufacturers able to use a lower cost valve seat.
Lead did NOT lubricate the cylinder wall. Also cureent gasline additives along with better metallurgy have reduced the wear problems, that lead didn't even address. Think about it, it is not uncommon for a car to go 1500,000 - 200,000 miles today without havinghte engine rebuilt. in the old dddays of leaed gasoline, an engine that made it to 100,000 miles was considered a miracle. And the level of degradation that caused an engine to be rebuilt was lack of compression due to worn rings and cylinders, along with erodded valve seats (using soft materials and relying on the lead to handle shock loads).
Lead does NOT retard the combustion of gasoline. It reduces the tendancy to detonation, which is the saame as saying it increases the octane rating. Detonation is caused by a physical change to certain fuel molecules due tothe heat and pressure of combustion. They actually get reformed into compression ignitable compounds. Higher octane means teh fuel is more resistant to this occuring. Lead reduces this tendancy in gasoline molecules. Octane had NOTHING to do with burn rate.
Lead doesn't stop spark knock pinging directly. Lead increse octane, which allows more spark advance before detonation. The same thing with any form of incease in octane.
Unleaded fuels do not cause excessive carbon buildup. Excessive carbon buildup is vcaused by excessive fuel, aka a rich mixture. It can also be casued by excessively lean mixtures which are so lean they don't fully combust. This was the problem with late 70s - early 80s carbureted engines. Trying to make a carb run very lean, meant lots of the time it was running too lean. In the past, with carburetors and no concern of fuel economy, rich mixtures were used for more power, and rich mixtures allw high compression ratio for a given octane of fuel.
Carbon build up DOES cause preignition, which is NOT the same as detonation.
Fuel injected engiens don't run on. They can't. Run on is caused by carbon buildup bombined with a carb. Carbs deliver a fuel air mixture as long as air is being drawn through them. And with an engine driven fuel pump, as long as the engine was turning, fuel was delivered. The hot spots of carbon buildup allowed marginal ignition, so the engine kept turning and fuel and air ws delivered, so run on. This became a big problem in teh late 70s - early 80s due to the attempts to make carbs run lean for emissions. A fuel injection system shuts off the fuel when you shut off the ignition. No fuel, no run on. Also since the electric fuel pump also shuts off, there is no possiblity of fuel being delivered allowing run on.
The reason for the removal of lead from gasoline was th ecomng of the catalytic convertor. Cats are poisoned by lead adn stop working. The lead in gasoline was removed to allow cats to be used. That was why the cars of the 70s came in two versions, leaded gas cars, adn unleaded only gas cars. Yes, lead was finally removed from ALL road going fuels due to the problems with lead emissions, but that came almsot 10 years after the adoption of unleaded fuels due to cats. BTW aviation gasoline still uses lead.
NOdbody said to run the car well in excess of legal speeds, just do full throttle runs to redline in thoe gers that allow you remain reasonably legal. That DOES clean out deposits.
The one fully correct thing is using a VERY small stream of water to clean out carbon. The only thing is, modern engines running fuel injection and unleaded fuels don't have much carbon buildup. Heads I have pulled off of modern engines are pretty much free of carbon buildup, unlike the carbureted cars of the late 60s and 70s that I pulled heads on. So even this is not necessary.
ANd BTW, there are things called PARAGRAPHS that make your longer posts easier to read.