Dirt Buildup

• Over a long period of time, dirt gradually builds up both inside and outside the tubes that constitute the heat transfer zone. Most quality heat exchangers have a design feature called a "fouling factor." This means they are designed with an excess amount of capacity so they will continue to operate at an acceptable level even after they become moderately dirty. Beyond a certain point, the heat exchanger will have to be properly cleaned. Unless you really know what you are doing, it is best to bring it into a shop for cleaning.
  
  

Organic Debris

• If you take your heat exchanger into a shop, be sure the employees are experienced. Cleaning a marine heat exchanger is usually a two-step process. The first step involves getting rid of large chunks of debris. Rinse the heat exchanger with a rather strong alkaline solution that will remove large organic material such as dirt and oil.
  
  

Scale

• The second step involves removing scale buildup resulting from minerals found inside the water. Using an acid solution, rinse the heat exchanger thoroughly multiple times.
  
  

Less Thorough Cleaning

• If your heat exchanger requires a less thorough cleaning, there is no need to remove the device. Simply take a long brush with a small diameter -- similar to what is used to clean a rifle barrel -- and brush the insides of the tubes on the side where the water enters the system. This is where most of the dirt buildup will be found. It is not recommended for inexperienced cleaners to use an acid solution while the device is still attached to the engine.