398S87302-0 Tohatsu LOWER UNIT ASSEMBLY "L"

Probable Causes
Leaks in hoses or connections
Leaks in the radiator and/or expansion tank
Leaks in the heater
Leaks in the water pump
Cylinder head gasket leakageRecommended Repairs
Leaks in Hoses or Connections
Check all hoses and check all connections for visual signs of leakage. If no leaks are seen, look for damage to hoses or loose clamps.Leaks in the Radiator and/or Expansion Tank
Pressurize the radiator and the expansion tank with the 9S-8140 Pressurizing Pump and check for leaks.Leaks in the Heater
Pressurize the cooling system with the 9S-8140 Pressurizing Pump and check for leaks.Leaks in the Water Pump
Check the water pump for leaks before starting the engine. Start the engine and look for leaks. If there are leaks at the water pump, repair the water pump or install a new water pump.Leaks in the Cylinder Head Gasket
Look for leaks along the surface of the cylinder head gasket. If you see leaks, install a new head gasket. Tighten the bolts that hold the cylinder head to the proper torque according to the Specifications Manual.Coolant Leaks At The Overflow Tube
Probable Causes
Faulty pressure cap
Abnormally high coolant temperature
Insufficient expansion tank capacity
Leaks in the cylinder head gasket or cracks in the cylinder head or the cylinder blockRecommended Repairs
Faulty Pressure Cap
Check the sealing surface of the pressure cap for damage. Also check the sealing surface of the radiator for damage. Ensure that the cap is sealing correctly. Check the opening pressure of the pressure cap valve with the 9S-8140 Pressurizing Pump. Also check the sealing ability of the pressure cap valve with the pressurizing pump.Abnormally High Coolant Temperature
As the temperature of the coolant increases, the pressure inside the cooling system increases. When the coolant overheats, the pressure will overcome the sealing ability of the radiator cap. This will cause coolant loss through the overflow tube. If the temperature of the coolant is running too high, refer to Troubleshooting, "Coolant Temperature Above Normal".Insufficient Expansion Tank Capacity
The expansion tank can be a part of the radiator or the expansion tank may be a separate unit. The expansion tank capacity must be large enough to contain the coolant as the coolant expands. Ensure that the expansion tank is installed correctly. Ensure that the size meets the recommendations of the OEM.Leaks in the Cylinder Head Gasket or Cracks in the Cylinder Head or the Cylinder Block
Remove the radiator cap while the engine is running. Look for air bubbles in the coolant. Bubbles in the coolant are an indication of a leak in the head gasket. Remove the cylinder head from the engine. Check the cylinder head and the cylinder walls for cracks. Check the head gasket surface of the cylinder block for cracks. Install a new head gasket. Tighten the bolts that hold the cylinder head to the proper torque according to the Specifications Manual.Internal Leaks
Probable Causes
Erosion or cracks in the unit injector sleeves
Cylinder head gasket leakage
Cracks in the cylinder head
Cracks in the cylinder blockRecommended Repairs
Erosion or Cracks in the Unit Injector Sleeves
If fuel is detected in the coolant, a possible cause is a faulty unit injector sleeve. Remove the unit injectors and inspect the sleeves for cavitation erosion or cracks. Replace any faulty sleeves. For the proper procedure for the removal and for the installation of unit injectors, refer to Disassembly And Assembly, Tool Operating Manual, NEHS0738, "Using the Injector Seating Tool " and Tool Operating Manual, NEHS0610, "Using the 128-8822 Tool Group on 3114, 3116, and 3126 Engines with Mechanical Unit Injectors (MUI)". Also, refer to Video Tape, LEVN4032, "Troubleshooting Guide for the 3100 Family of Diesel Engines" and Video Tape, LEVN4732, "Injector Seating Procedure".Leaks in the Cylinder Head Gasket
Cracks in the upper surface of the cylinder head can allow coolant to leak into the crankcase. Cracks that are in an area that is between a water passage and an opening into the crankcase can also allow coolant to leak into the crankcase.Cracks in the Cylinder Head
If the cylinder head gasket leaks between a water passage and an opening into the crankcase, coolant will get into the crankcase.Cracks in the Cylinder Block
Cracks in the cylinder block that are between a water passage and the crankcase will allow coolant to leak into the crankcase.