I was wondering what they are and how you get them. I was told you can get them when changing the thermostat or changing or adding coolant. However, I was told that 240s don't get air bubble problems. And if they do, the bubbles in the system will go away eventually. Are air bubbles in the cooling system a big concern, and if you have them will they go away by themselves through a few minutes of driving?

Hello,

As you have heard, most bricks don't have that particular problem. First make sure there are no obvious leaks. Then WITH THE ENGINE STONE COLD!!!! remove the expansion tank cap, you may get a little hissing here, that's okay. Now, set the heat control to HOT and start the motor, gently revving it(no more than 3k) to bring it to normal operating temperature and allow it to idle for 10 mins or so and the bubbles should work their way out.

Happy Bricking!!!!

Richard
87 245 DL 338,000 km and counting
84 244 Turbo Intercooler (real man's toy)

There's a little pintle valve on the thermostat that is supposed to allow trapped air to escape. If you follow the above advice and don't get rid of the air bubbles, check for a possible head gasket leak, that is allowing exhaust gas to enter the cooling system. This can be done by using a leak down tester, and/or testing the coolant tank for the presence of exhaust fumes. A good shop can do both of these tests. One thing you can do is to see if you're losing coolant with no obvious external leak (e.g., hose, water pump, etc.). If so, what may be happening is this. When the car warms up and the cooling system gets pressurized and then the engine is stopped, a blown head gasket can allow coolant to escape into the cylinder. You can test for this by driving the car to warm it up (with the coolant reservoir cap screwed down snug), shutting the car down, and then removing the spark plugs. Wait 15 minutes and then spin the engine over and see if any coolant comes out of the spark plug holes.