0431879 JOHNSON CARB. ASSY., Lower, 40AR, 40R only

Personal injury can result from escaping fluid under pressure.If a pressure indication is shown on the indicator, push the release valve in order to relieve pressure before removing any hose from the radiator.
Check the coolant level in the cooling system. Add coolant, if necessary.If the coolant level is too low, air will get into the cooling system. Air in the cooling system reduces coolant flow. Air creates bubbles that contribute to cavitation. Bubbles in the coolant also reduce the cooling capability.
Check the quality of the coolant. The coolant should have the following properties:
Color that is similar to new coolant
Odor that is similar to new coolant
Free from contamination
Properties that are recommended by the engines Operation and Maintenance ManualIf the coolant does not have these properties, drain the system and flush the system. Refill the cooling system according to the engines Operation and Maintenance Manual.
Check for air in the cooling system. Air can enter the cooling system in different ways. The following conditions cause air in the cooling system:
Filling the cooling system incorrectly
Combustion gas leakage into the cooling systemCombustion gas can get into the system through the following conditions: internal cracks, damaged cylinder head, and damaged cylinder head gasket. EGR cooler failure may result in combustion gas entering the engine coolant.
Inspect the radiator (if equipped) and the air-to-air aftercooler (if equipped). Make sure that the air flow is not restricted. Look for the following conditions. Make corrections, if necessary:
Bent fins
Debris between the folded cores
Damaged fan blades
Check the heat exchanger (if equipped) for internal blockage. Make sure that the filters for the water are not clogged.The condition of the water that is circulated through the heat exchanger can decrease the effectiveness of the heat exchanger. Operating with water that contains the following types of debris will adversely affect the heat exchanger system: silt, sediment, salt, and algae. In addition, intermittent use of the engine will adversely affect the heat exchanger system.
Check the pressure cap.If the pressure cap does not maintain the correct pressure on the cooling system, the engine could overheat. A decrease in cooling system pressure reduces the temperature of the waters boiling point.
Inspect the cooling system hoses and clamps.Damaged hoses with leaks can normally be seen. Hoses that have no visual leaks can soften during operation. The soft areas of the hose can become kinked or crushed during operation. These areas of the hose restrict the coolant flow. Hoses can crack after a period of time. The inside of a hose can deteriorate and the loose particles of the hose can restrict the coolant flow.
Check the water temperature regulators.A water temperature regulator that does not open or a water temperature regulator that only opens part of the way can cause overheating.A water temperature regulator that does not close enables overcooling.
Check the engine water pump.Check for a fluid leak from the pumps weep hole during engine operation and check for a leak when the engine is stopped. If either coolant or oil is leaking from the weep hole, replace the pump.A water pump with a damaged impeller does not pump enough coolant for correct coolant flow. This affects the engines operating temperature. Remove the water pump and check for damage to the impeller. Also inspect the inside of the pumps housing for scratches from the impeller.
Check the aftercooler.A restriction of water flow through the aftercooler can cause overheating. Check for debris or deposits which restrict the free flow of water through the aftercooler.
Check the Exhaust Cooler (NRS) cooler.Inspect both ends of the cooler at the hook ups for leaks. Inspect the coolant lines going into the cooler. Refer to Testing and Adjusting, "Exhaust Cooler (NRS) - Test" if a leak is present on either end of the cooler.