I have a 2007 335i BMW and there is water dripping right behind the right passenger tire from the door frame. I just had the water pump, thermostat, expansion tank and hose replaced about a month ago. Could this be a problem with these items?

SOURCE: Water leak from top of expansion tank.2000 BMW 316i se

The water (coolant) in the expansion tank will rise and fall with the engine temperature. What the expansion tank does is collect and return coolant to and from the engine. When the engine warms up the coolant gets hot, builds up pressure and opens up the radiator cap. The coolant then goes into the expansion tank. Now when the engine cools down the pressure drops in the cooling system and the pressure drop (vacuum) pulls the coolant back into the engine via the radiator cap. The radiator cap allows the cooling system to build up pressure and by doing so increases the boiling point of the coolant, but when that pressure exceeds the caps rating the cap opens and the coolant goes to the expansion valve. The cap has another part to it that when the engine cools down and a partial vacuum is created in the cooling system a "valve" in the radiator cap opens and allows the coolant to be drawn back into the engine. I would look at your radiator cap to see if any gunk or build up is on it, and check the rubber gaskets for cracks. It's easiest just to replace the cap because they are inexpensive and easy to replace (2-10 dollars). The expansion tank should have two hoses on it. The one on the bottom comes from the radiator and the one on the top (possibly part of filler cap) runs down and is open to the ground. That way if it is overfilled or becomes overfilled it will slowly leak onto the ground. When and if you change your radiator cap, make sure the engine is cooled down, remove cap and start engine and turn heater to full blast, full heat. Leave the cap off and let it run until engine warmed up. This should burp out any air pockets that may have happened when coolant was changed. Also top off the coolant in the radiator while it is running. Hope this helps and good luck

SOURCE: Water leaking from top of expansion tank.

have you replaced the bleeder screws? and the expansion tank cap they both have O-rings that compress and will fail over time also check the hose at the top of the exp tank it also has o-rings inside it

SOURCE: coolant leak and overheating

I had a water leak on my 730i I found it after much trouble.A hairline crack in the plastic thermostat housing which onlly opened up when hot and of course got worse as water level dropped.Hope this helps.

SOURCE: bmw 745i 2003 water leaks out from front of motor

I had this same problem in my 02 745i... It's leaking from the internal coolant pipe... a $.05 rubber ring is going to cost you 3-5k easily.

SOURCE: overheating: 1999 bmw 323i m series 2.5

the water pump and thermostat should have solved it. an air pocket can cause that but usually not to that degree.

don't get one of those cheap *** plastic impeller water pump for sissies. Get the metal impeller one. get a cool running thermostat and drill two 3/16" holes in it 180 degreess from each other. you may have installed the t-stat backwards.