As your coolant solution heats up, it expands. This design works fine, as long as your coolant doesn’t get too hot. This prevents any leaks as well as any dirt or debris from entering the cooling system. In order for this cooling system to work effectively, it needs to be sealed. The coolant is transferred back and forth between the tank and cooling system depending on the pressure. The radiator coolant overflow tank works by filling the tank with coolant when the cooling system’s pressure is too high and withdraw coolant from it when there is under pressure in the system. How a Radiator Coolant Overflow Tank Works It really does do a brilliant job of this too. This amazing piece of engineering is designed to keep your engine operating at a constant 90 degrees centigrade, whether you’re flying along the motorway, or stuck in traffic. As your engine turns over and gets hot, the coolant that passes through and around your engine steals this heat away and carries it to the front of the car where it’s cooled off by the radiator and cooling fans. Your vehicle’s cooling is simply designed to cool the engine by carrying its generated heat away. This is where your cooling system comes into place. It needs a system in place to take away the heat that’s generated from the engine to stop it from overheating. So your car needs a system in place to provide an efficient means of cooling. So hot in fact, that it can cause parts of your exhaust to glow bright orange! My plan tomorrow is to disconnect the upper and lower rad hoses at the thermostat and force water thru, to check for any blockages, then crank the engine to see if water is being moved by the water pump (I checked the return line in the expansion tank and there is a flow, although it seems weak to me).Īs mentioned I don't have much experience with these, but it seems to be a pretty basic system.As you’re probably already aware, your engine gets incredibly hot as you drive.

Back flushed the heater core and have good flow in both directions. I replaced the expansion tank cap and installed an OEM thermostat as the other shop used aftermarket parts.

Found 2 small leaks, one a hose clamp and one an O-ring I switched out. We left the pressure tester on overnight and it dropped about 5psi. After that I put some pressure into the system with a pressure tested and then bled any air from the thermostat bleed screw. I started with a vacuum bleed as per Mini's coolant fill procedure. There's no signs of coolant and oil mixing anywhere, and there's no bubbles in the tank when its running, and no external leaks. I checked compression - good and even across all 4. They told him it must be his head gasket. The previous shop replaced: Turbo (No one can tell me why), water pump, aux water pump, rad and thermostat. The Electric fan does work and will run on for a few minutes after shutting it off. The upper rad hose and heater hoses are hot, but the lower hose is cold. The heat from the blower is sometimes good sometimes not, like a typical air lock, which was my first guess. There's no temp gauge in the car and no overheating message never gets displayed, but the expansion tank will puke a little out thru the cap. The vehicle overheats after about 30 minutes of driving, but only once you come to a stop and/or shut it off. I don't have a lot of experience with Mini's but wanted to try to help the guy out. Hi guys, I received a 09 Mini Cooper S that had come from another shop which gave up.

Coolant tank