A blown head gasket
Thermostat and radiator
There are several causes that will reduce the water level in your car radiator. The most common cause is evaporation. Engine overheating will also reduce the radiator water level.
There could be many reasons for this, thermostat bad or weak, cooling fluid low, weak water pump, fan not operating properly, radiator hose weak, plugged radiator.
That will vary greatly among different engine designs. Some V12's displace over 24 Liters others are small as 4 Liters (relatively small haha). If you are changing your coolant then make sure the bottom radiator hose is attached and fill the engine block with a 50/50 mix of antifreeze and water through the thermostat housing (thermostat removed of course) reinstall the thermostat, connect the upper radiator hose and fill the radiator with the 50/50 mix. Close the radiator cap and run the engine for 5 mins, shut her down and refill the radiator. Job done! -CJP
I would start at the thermostat. Problems with the radiator and head gaskets are usually presented as visual leaks. But clogged passages in the radiator would also cause overheating issues, so have the cooling system flushed.
Can be the thermostat which is cheap to replace, or it might be the head gasket which is expensive.
Plugged radiator, Bad thermostat, water pump not working, radiator hoses collapsing and dont forget no oil
The thermostat is located on the front bottom of the engine. You can follow the radiator water hose from the radiator to the thermostat.
Low coolant, plugged radiator, inoperative radiator fan, failed water pump, head gasket, thermostat.
Remove the top water line from the radiator to the water pump. The thermostat is found there.
Low coolant, inoperative radiator fans, stuck thermostat, failed water pump, restricted radiator, head/headgasket.
Low coolant, inoperative water pump, head gasket failure, inoperative radiator fan, etc.
/ Follow the top radiator hose down to the water outlet on the engine; the thermostat is in there. Follow the top radiator hose down to the water outlet on the engine; the thermostat is in there.
The thermostat is located in the water inlet where the radiator hose connects from the radiator to the engine.
Bad radiator fan motor; bad radiator fan relay; clogged radiator; thermostat stuck closed; loose belt; bad water pump; hoses leaking;
Once the thermostat has opened, the hot coolant flows from the thermostat housing on the engine into the top of radiator and out the bottom of the radiator back into the water pump.
Causes include low coolant, inoperative radiator fan, plugged radiator, stuck thermostat, water pump malfunction, head gasket failure.