3AS-07709-0 Tohatsu OILPAN SUB-ASSEMBLY

Cetane Number
The cetane number of the fuel effects the ability of the engine to start. Also, the cetane number effects the interval of time before the engine runs smoothly. Fuels of high cetane rating are easier to ignite. The starting temperature can be improved approximately 7 to 8°C (12 to 15°F) for every increase of ten in the cetane number. After the engine reaches the normal operating temperature, a change in the cetane from 40 to 50 will have a minimal effect on engine performance.Most fuels that have a cetane number above 40 will permit acceptable engine starts in warmer outside temperatures. The engine will start satisfactorily with this fuel when the engine is kept warm. The engine can be kept warm by using either a heated enclosure or a properly sized coolant heater.During average starting conditions, direct injection diesel engines require a minimum cetane number of 40. A higher cetane value may be required for operation in high altitudes or for cold-weather operation. The minimum fuel cetane number that is required for the precombustion chamber (PC) diesel engine is 35.Modifying the Cetane Number
The cetane number of a fuel can be changed if the fuel is mixed with a fuel that has a different cetane number. Generally, the cetane number of the mixture will be in direct relation to the ratio of the fuels that were mixed. Your fuel supplier can provide the information about the cetane number of a particular fuel.Additives can also be used to improve the cetane number of a fuel. Additives are evaluated through testing in special test engines. However, the characteristics of fuels with natural cetane number can be different than those characteristics of a fuel addetized to reach the same cetane number. While both fuels may be rated as having the same cetane number, starting may be different.Cloud Point
The cloud point of a fuel is different from the pour point. The cloud point is the temperature that allows some of the heavier components in the wax to solidify in the fuel. This wax is not a contaminant in the fuel. The wax is an important element of No. 2 diesel fuel. The wax has a high fuel energy content and the wax has a very high cetane value. Removal of the heavier wax lowers the cloud point of the fuel. Removal of the wax also increases the cost because less fuel can be made from the same amount of crude oil. Basically, a No. 1 diesel fuel is formulated by removing the wax from a No. 2 diesel fuel.The cloud point of the fuel is important because the cloud point can limit the performance of the fuel filter. The wax can alter the fuel characteristics in cold weather. Solid wax can fill the fuel filters. The solidified wax will cause filter plugging. Plugged filters cannot remove contaminants from the fuel and hence cannot protect the fuel injection systems. Since fuel must flow through the filters, installing a fuel heater is the most practical way to prevent the problem. A fuel heater will keep the fuel above the cloud point as the fuel flows through the fuel system. The fuel heater will permit the wax to flow through the filters with the fuel.Modifying the Cloud Point
You can lower the cloud point of a diesel fuel by mixing the diesel fuel with a different fuel that has a lower cloud point. No. 1 diesel fuel or kerosene may be used to lower the cloud point of a diesel fuel. The efficiency of this method is not good, because the ratio of the mixture does not have a direct relation to the improvement in cloud point. The amount of fuel with low cloud point that is required makes the process less preferable to use.The fuel supplier must be consulted to provide the proper mix of fuels that offers the appropriate cloud point.Another approach to modify the cloud point is to use cold flow improvement additives. The manufacturer of the fuel can add cold flow improvers to the fuel. Cold flow improvers modify the wax crystals in the fuels. The cold flow improvers do not change the cloud point of the fuel. However, the cold flow improvers keep the wax crystals small enough to pass through standard fuel filters. For mixing precautions, see the section "Pour Point".Generally, the most practical method that is used to prevent problems that are caused by fuel cloud point at low temperatures is the use of fuel heaters. In most applications, fuel heaters can be used at a lower cost than fuel mixtures.The common standard methods that are used to test the cloud point of diesel fuels are:
"ASTM D2500" Test Method for Cloud Point of Petroleum Products
"ASTM D5771" Test Method for Cloud Point of Petroleum Products (Optical Detection Stepped Cooling Method)
"ASTM D5772" Test Method for Cloud Point of Petroleum Products (Linear Cooling Rate Method)
"ASTM D5773" Test Method for Cloud Point of Petroleum Products (Constant Cooling Rate Method)Pour Point
The fuel's pour point is a temperature below the cloud point of the fuel. Fuel stops flowing below the pour point. The pour point is the temperature which limits movement of the fuel inside the pumps.To measure the pour point, the fuel temperature is lowered below the cloud point in steps of 3°C (5°F) at a time. The temperature is lowered until the fuel does not flow. The pour point is the last temperature that is shown before the flow stops. At the pour point, the wax has solidified out of the fuel. This temperature makes the fuel more solid than liquid. The pour point of the fuel can be improved. This improvement does not require the removal of important elements. This process is the same process that is used to improve the cloud point of a fuel.A fuel's pour point should be at least 6°C (10°F) below the lowest ambient temperature that is required for engine start-up and for engine operation. To operate the engine in extremely cold weather, No. 1 fuel or