854874 Volvo.Penta Drive

FLOW OF COOLANT (SCHEMATIC)
1-Aftercooler. 2-Elbow. 3-Exhaust manifold shields. 4-Cylinder head. 5-Temperature regulator housing. 6-Radiator. 7-Flywheel housing. 8-Cylinder block. 9-Oil cooler. 10-Water pump. 11-Inlet pipe. 12-Bypass line.The coolant flows from the cylinder heads, through the elbows (2) to the exhaust manifold shields (4). The coolant circulates through the exhaust manifold shields and forward to the temperature regulator housings (5) at the front of each exhaust manifold.
FLOW OF COOLANT
1-Aftercooler. 2-Elbow. 4-Cylinder head. 5-Temperature regulator housing. 7-Flywheel housing. 8-Cylinder block. 9-Oil cooler. 10-Water pump. 11-Inlet pipe. 12-Bypass line.Regulators, positioned in each housing, control coolant flow to the radiator to regulate the temperature in the cooling system. Coolant can be directed to the radiator from either the left or right regulator housing or from both sides. When the flow is from only one side a crossover tube connects the two housings.A bypass line (12) extends from the inlet side of the temperature regulator housings to the inlet side of the water pump. When the temperature of the coolant is not high enough to open the regulators, coolant bypasses the radiator to circulate through engine, assuring quick warm-ups. A portion of the coolant flows through the bypass line at all times.Overheating
If difficulty is experienced with the engine overheating, check the following possible causes:1. Coolant Level. Insufficient water in the cooling system. If the coolant level has been allowed to fall so low that the coolant is no longer circulating, the engine should be stopped immediately and allowed to cool before adding coolant. If there is still good circulation, add makeup coolant slowly while the engine is running. These precautions will minimize the possibility of cracking the cylinder heads.2. Fan. Loose fan belts.3. Radiator Clogging - (External) Accumulation of leaves, mud and debris around the radiator core. In some cases, these accumulations can be removed by flushing with water or compressed air from the back of the radiator. It may become necessary, eventually, to remove the radiator guard to clean the cores effectively.4. Water Temperature Regulators. Failure of water temperature regulators to open. Check the regulators for opening temperature as described in the topic TESTING TEMPERATURE REGULATOR. Observe the amount of scale deposited on the regulators. Too much scale will obstruct operation. The engine should not be operated with a regulator removed.5. Water Pump. A badly corroded or worn water pump impeller or impeller loose on the shaft.6. Internal Clogging. Excessive scale or sediment deposits in the radiator, cylinder head or block. Such deposits can cause serious damage to the engine, by retarding the transfer of heat from the head and cylinders to the coolant. In such cases, the water temperature may not be above normal. However, loose scale and sediment may deposit in water passages to such an extent that circulation will be retarded, in which case the water temperature may go above normal.To check for lime and scale in the cooling system, remove one of the precombustion chambers and inspect the surface which comes in contact with the coolant. To remove hard scale, follow the direction in accordance with the Lubrication and Maintenance Guide.7. Continuous Overload. Operating an engine at a continuous overload, which lugs the engine speed below its rated speed, may also cause overheating. As a correction, the load on the engine should be reduced.8. Altitude. The altitude at which the engine is operating should be considered when overheating is encountered. The horsepower of the engine is decreased as the altitude increases. Also, the boiling point of water is lower at higher altitudes.9. Water Temperature Indicator. It may be that the indicator is not registering correctly. If the indicator is suspected of giving a false reading, install a new one and check the reading.10. Overheating can be caused by combustion gases escaping by the precombustion chamber gaskets, cylinder head gaskets or water ferrules and seals. The gases can accumulate in the cylinder head and block, thus restricting the flow of coolant through the cooling system. Thus, the coolant temperature rises rapidly and hot spots will exist in the cylinder head. The easiest method of checking for this condition is to carefully remove the radiator cap and check for air bubbles in the radiator. If air bubbles are present in the cooling system, check the precombustion chambers for tightness and, if necessary, replace the gaskets.