Aircraft engines are designed to run with large clearances. The reasons for this include the age of their design, the materials used, and most importantly the fact that they are air-cooled. Large clearances between pistons and cylinders lead to large amounts of blow-by, the gas that leaks by the piston rings during the high-pressure combustion events. Blow-by gas is made up of combustion by-products such as carbon dioxide and water. It is also the source of lead found in the oil. It also contains partially combusted fuel (very reactive) and raw fuel. An engine that uses 15 gallons of fuel per hour may put 0.5 gallons of partially combusted and raw fuel into the crankcase per hour. This highly reactive mixture chews up the additives in the oil. Most of these fuel components are volatile and the vapors exit the engine through the crankcase breather. Other components are less volatile and remain in the engine diluting the oil. It is the blow-by gas that contaminates the oil and gives it that characteristic smell after only a few hours.
The blow-by components that remain in the oil are real troublemakers. They not only dilute the oil and additives but in the upper ring zone they overwhelm the dispersant and antioxidants leading to carbon and lead deposits. Analysis of deposits found in the upper piston ring groove show them to contain over 2% lead and therefore fuel derived. Oil companies only put enough antioxidant to protect the bulk oil from oxidizing. This however is not the problem. CamGuard uses multiple high molecular weight antioxidants to address this “blow-by fuel dilution” unique to aircraft engines. The result is fewer deposits, which dramatically reduces the chance of sticking piston rings or valve guide “morning sickness”.
High Pressure Differential Scanning Calorimetry (HPDSC) is used to directly measure an oils resistance to oxidation and tendency to form deposits. A small oil sample is placed in a high-pressure cell under150psi of oxygen, where it is heated to a temperature of 200° (392°F) and held constant. The time to the onset of oxidation in minutes, determined by the instrument by release of heat, indicates the oils stability. The longer the time the better.
We tested a popular 15W-50 semi-synthetic oil with and without the addition of 5% CamGuard. The results show a huge increase in the time to oxidation with the use of CamGuard. The substantial increase in oxidation stability when using CamGuard is very important in air-cooled aircraft engines as explained above.