BMW 525i Overheating, already changes thermostat, water pump < what do I check or do next...car has 110K miles

Hard to say with out being able to diagnose it in person. BUT! I have seen on few occasions the impeller either disintegrate or come off the water pump shaft. I would also make sure that the coolant is full. sometimes an air pocket will cause the cooling system to "air lock" not allowing coolant to flow properly if not refilled properly.

2006 bmw 530xi have a electric water pump (next to the thermostat). Common to go bad. There should be no heat in the car and "overheating" pops up. Electric water pump $495.00

I am not aying that this is what I think it is but I found this on your year BMW

Some BMW, Volkswagen and Audi cars have a common problem that the water pump impeller becomes dislodged from the input shaft of the water pump leaving the water pump looking ok from the outside, but failed on the inside. If your car experiences this problem it will over heat rapidly much like a thermostat failure. For exact specific repair procedures for this repair visit our online repair manual page.




Failed BMW, VW, Audi Water Pump Troubleshooting Procedure

• Check Water Pump Operation - To troubleshoot this problem first drain about a half a gallon out of the cooling system, next remove the thermostat from the engine. With the thermostat out start the engine (stand back) coolant should be forced out of the thermostat port, if not the impeller has dislodged itself from the water pump input shaft and needs to be replaced. To replace the water pump finish draining the remainder of engine coolant, remove the serpentine belt and coolant hoses. Next remove the water pump mounting bolts and remove the water pump. Clean gasket surfaces and reinstall new water pump and reassemble. Refill with coolant and recheck system, top off engine coolant after it has re-cooled.

Hi, Sounds like you have tried about everything. Ok the aux. coolant switch is for the electric pump for the heater core will not cause an over heating condition just a longer warm up of the heater core. Has the cooling system been bleed properly if there is a trapped air pocket it will not let coolant circulate. Was the new thermostat installed correctly? They have a vent that needs to be towards the top or they trap air on the back side and cant take an accurate reading to open and close. Other areas to look at would be proper operation of the fan clutch, if they fail they can cause the fan to not lock up properly and supply enough air movement through the radiator. The aux. electric fans and their temp switches do you hear them coming on are they coming on at the right temp.

Are you loosing any water from the radiator or fill up tank?
I would change the Thermostat for starters. they are not expensive and most of the time are the cause of a car overheating.

There are 4 things it could be! First your radiator or cooling fan is not turning on, this could be from a fuse. 2nd your thermostat needs replaced about 3-7 dollars for part. 3rd your water pump needs replace..about 150 to 300 dollars..If you can run for more then 10-15 miles then it shouldn't be your water pump. 4th your low on anti-freeze and need to add some into radiator!
Good Luck!
Hope this helps
PS to check fluid level under hood of car, wait until car is cooled to remove cap. And if you were low, you might want to check underneath your car to see if your leaking anywhere...

you might have a blown head casket try due a pressure test on each cylinder and sometimes you can take a spark plug out 1 by 1 and just tap the ket so it cranks and see if water comes out of the cylinder

check if the water is circulating as you might have a blockage in the header tank. this can be checked by opening the radiator cap and check if the water is circulating on top.

first check coolant level .if all good replace thermostat .look at water pump drive belt make sure it is not slipping.if all is good i am looking at a bad water pump.

You actually need the thermostat in to pressurize your cooling system or the coolant won't cyle through the radiator, it'll just cycle around the engine. Most people think without the thermostat in the coolant will just pump freely through the engine and radiator, but it doesn't.

Chuck in a new thermostat, purge the air out of the system and see if it overheats then. I gaurentee it won't, if it does then you've got head problems (but they should already be obvious by now).