7746630_139 Volvo.Penta Control unit

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. Refer to Operation and Maintenance Manual, "Cooling System Coolant Level - Check". If the coolant level is too low, air will get into the cooling system. Air in the cooling system will cause a reduction in coolant flow and bubbles in the coolant. Air bubbles cause a reduction in the cooling of engine parts.
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 dirt and debrisIf the coolant does not have these properties, drain the system and flush the system. Refill the cooling system with the correct mixture of water, antifreeze, and coolant conditioner. Refer to Operation and Maintenance Manual, "General Coolant Information".
Check the coolant mixture of antifreeze and water. The mixture should be approximately 50 percent water and 50 percent antifreeze with 3 to 6 percent coolant conditioner. Refer to Operation and Maintenance Manual, "General Coolant Information". If the coolant mixture is incorrect, drain the cooling system and flush the cooling system. Refill the cooling system with the correct mixture of water, antifreeze, and coolant conditioner.
Check for air in the cooling system. Air can enter the cooling system in different ways. The following items are some of the most common causes for air in the cooling system:
Filling the cooling system incorrectly
Combustion gas leakage into the cooling system
Loose hose clampCombustion gas can get into the system through the following conditions: inside cracks, damaged cylinder head and damaged cylinder head gasket. A loose hose clamp can allow air into the cooling system during the cooldown period. Air in the cooling system causes a reduction in the cooling capacity of the coolant.
Check the fan drive system. A fan drive system that is not turning at the correct speed can cause improper air speed across the radiator core. The lack of proper air flow across the radiator core can cause the coolant not to cool to the proper temperature differential.
Check the water temperature gauge. A water temperature gauge which does not work correctly will not show the correct temperature.