It’s A Dirty Job, But Someone Has To Do It

Carbon build-up affects engine performance, component wear and fuel economy.

Throughout the history of the automobile, dirt, in one form or another, has always been the enemy. It causes engine performance problems, excessive and premature wear of parts and components. In short, dirt is just an overall nuisance. One type of “dirt” that many people fail to take into account is carbon that builds up on engine valves, combustion chambers and pistons. This build-up can result in a host of problems ranging from poor fuel economy to engine misfire.

For many reasons, carbon build-up has become much more of a problem in recent years than it was in the past. Carbon, along with “traditional” dirt, is wreaking havoc in engines, large and small (see page 36 for some How To tips on tackling carbon build-up problems).

As is detailed in that article, dirt build-up in the throttle body causes rough idle and other driveability problems. Dirty air filters can reduce fuel economy. And dirty spark plugs can cause engine misfire. But let’s get back to the dirt and carbon deposits inside the engine.

Carbon Deposits Due to Combustion

Why has carbon build-up become more of a problem in recent years? First of all, people are keeping their cars longer than ever before. In 2008, the average age of the family car is nearly 9 years. It was less than 7-1/2 years in 1993, 15 years ago. It goes without saying that an older car will have more internal engine deposits. These deposits are the result of combustion.

When the fuel mixture burns, one of the byproducts is carbon because there is no such thing as perfect combustion. If perfect combustion did exist, the only byproducts would water vapor, carbon dioxide and nitrogen. No carbon, no deposits. But let’s get back to the real world where incomplete combustion is the rule.

Don’t forget that an older engine will exhibit more wear (increased piston skirt-to-cylinder wall clearance) that allows more oil to leak past the rings. This oil is burned, leaving more deposits in the combustion chamber.

The second reason, and a more likely one, is gasoline. There has been a significant change in the amount of cleaning additives that are blended into gasoline. In 1995, the EPA established the lowest additive concentration (LAC) required in gasoline. In other words, this mandate stated that all gasoline had to have a minimum amount of additives that would control deposits in the fuel system and combustion chamber. At that time, many brands of gasoline were blended with additive treat rates (the amount of additive per volume) that exceeded this minimum. In response to this law, refineries and terminals began reducing treat rates.

Over the last 13 years, the treat rate of LAC additives, or the content of deposit control additives in gasoline, has decreased significantly (by almost 50%). As a result, deposits and carbon build up in the engine and fuel system of all vehicles has increased. And don’t forget that today’s engines are more sensitive to carbon build up due to tighter manufacturing tolerances than those used in the past.

The Effects of Carbon Build Up

Carbon build up in the engine can be found in several locations, as shown in Figure 1. These include on the fuel injectors, A; on the intake valves, B; on the top of the piston, C; on the spark plugs; and in the combustion chamber, D. Some of the effects of these deposits can be observed by the driver, while others cannot.

First of all, engine smoothness will be affected. The driver will notice that the engine might start to idle rough, a sure sign of misfiring. Also, engine knock might be heard. Carbon deposits that build up on the piston crown and the combustion chamber can effectively increase the compression ratio. This would require a higher octane fuel, such as upgrading from Regular (87 octane) to Plus (89 octane). Drivers might also notice some cold start problems, along with a general lack of power, or poor performance from the vehicle.

Not as obvious are other problems that result from carbon build up. Those noticeable driveability issues mentioned previously are signs of inefficient combustion that increase the emission levels from the vehicle. Depending on the age of the vehicle and the region of the country, this can lead to a failed emissions test. In states where emission testing is done, a failed test will prevent the owner from renewing their license.

Accelerated engine wear can also be a problem. In many cases, such wear goes undetected until a major and costly problem surfaces. Finally, all of these symptoms affect fuel economy. And with gasoline prices at record high levels, your customer is getting hit in the wallet, too.

Combating Carbon

You’re probably asking yourself what can be done to remove these carbon deposits and how can such deposits be prevented from forming in the future. The answer is not an engine teardown to clean the valves, pistons and injectors. You don’t have to take such drastic measures. The answer is in a can: Mopar® Combustion Chamber Cleaner, P/N 04318001AB. Let’s review how to use this product.

If the engine is equipped with an air pump, disconnect it. Next, remove the throttle body air intake hose. Start the engine and run it at 750 rpm. Begin spraying the contents of the can directly into the throttle body. If the engine begins to stall, increase the engine speed, but run it just fast enough to prevent stalling. Spray the entire contents of the can into the engine.

When the can is empty, turn the engine off. Let it stand for 5 to 10 minutes as the cleaner does its magic. Restart the engine and run it at a low speed for about 5 minutes. This will completely expel the cleaner from the engine. Turn off the engine and reinstall the air intake hose and reconnect the air pump, if required. That’s it. It’s that simple to remove those harmful carbon deposits.

The next question is how does your customer prevent this carbon from building up again in the engine and causing the same problems. First of all, it’s important to keep the vehicle properly maintained. This includes replacing spark plugs at the recommended interval and being sure that the air filter is clean. These are tasks that optimize performance and minimize poor combustion.

It’s also important to recommend to your customers that they use a major brand name gasoline.