Radiator Cap: A faulty or damaged radiator cap can cause coolant to leak from the overflow tank.
Hoses: Check all the coolant hoses for cracks, bulges, or worn spots. Any damaged hoses should be replaced.
Water Pump: A faulty water pump can cause coolant to leak. Look for signs of coolant leaking from the weep hole of the water pump.
Cylinder Head Gasket: A blown cylinder head gasket can cause coolant to leak into the combustion chamber and be burned off.
Thermostat housing: The thermostat housing and gasket may also be culprits for a leak.
Heater Core: A leak in the heater core can cause coolant to leak inside the cabin of the vehicle.
Coolant Overflow Tank: Check the coolant overflow tank for cracks or damage and ensure that the vent hose is clear and not kinked.
Cracked Radiator: Inspect the radiator for cracks, especially at the seams and joints.
Faulty Radiator Hoses or Hose Connections: Check the radiator hoses and inspect for any cracks, looseness, or wear. Make sure the hose clamps are properly tightened.
Corroded Radiator Fins: Over time, the aluminum fins of a vehicle's radiator can experience corrosion, leading to tiny cracks and possible coolant leaks.
Faulty Radiator Cap: As previously mentioned, a faulty or loose radiator cap can result in coolant leakage through the overflow system.
Bleeder Screws: Check the condition and tightness of the bleeder screws, usually found on the engine's coolant passages and hoses.
Intake Manifold Gasket: Some vehicles have intake manifolds that can develop a gasket leak, causing coolant to seep into the engine's cylinders.
Heater Core In-Line Valve or Shut-Off Valve: Depending on the ST1100's design, there might be an in-line valve within the heater hose circuit. Check if these components are tight or may need replacement.
Pressure: An overly tight coolant system can cause increased pressure and lead to leaks in weaker areas of the system. Ensure the coolant system is pressurized according to specifications.
Cracked Engine Block or Cylinder Head: This is a less likely cause, but in rare cases, a severe cooling system issue or engine overheating can cause cracks in these major components, leading to coolant leakage.
If you've identified the source of the leak, it's important to properly repair or replace the faulty components. If the leak is extensive or difficult to diagnose, it's best to consult with a qualified mechanic. Ignoring coolant leaks can lead to engine overheating and other serious problems, so it's important to address them as soon as possible.
