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praiford 12-11-2012 04:44 AM

Coolant Leak
 
I have being trying to diagnose a coolant leak on my '05 545 for the past month. I don't see any leaks from the water pump or the timing cover area (the dreaded coolant pipe leak) while running. It happens over night or if the car has been parked for 3 or so hours.

I have ordered a new water pump and thermostat and plan to replace them this weekend. The pump is growling now and sounds like the bearings are going.

It "looks" like the leak is in the front area of the engine and sometimes it is pretty substantial from what is on the ground.

Anyone have experience with this or any thoughts/ideas?

Thanks.

bimmerfan52 12-11-2012 05:40 AM

Three common leak locations on 545i:

- Temperature sensor o-ring on the lower radiator hose
- Coolant expansion tank
- Vent tube (runs under shroud at front of engine bay from top of radiator on drivers side to expansion tank)

Last two will sometimes only leak after engine is shut off (both are involved in "relief valve" role of the expansion tank in the sealed coolant system).

If you have not performed preventive maintenance on your coolant system before, now is the time for a 2005. Belt driven water pumps are cheap for 545i and you'll want to do the thermostat, expansion tank, hoses, belts and fresh coolant. If your vent tube is not leaking now it probably will by the time you get done handling it during disassembly and reassembly. You can either replace the unit (around $40) or replace the plastic tube section with 5/16" copper tube for a permanent fix ($5).

Water pump replacement is not a bad job on the 545i. Biggest PITA is removing the fan and installation of the AC belt (if you don't have the right tool). Handle the plastic parts you are not replacing gently as they become brittle with age.

Consider any other preventive maintenance you may want to do while the car is apart (plugs, air filter, alternator, belt tensioner, etc).

You will have to remove the crankshaft harmonic balancing pulley to get to one of the water pump bolts. Plan on replacing those bolts which are aluminum "stretch" bolts and handle the balancing pulley carefully and set it in a safe place while off the car as they are pretty pricey and can be damaged if dropped on concrete.

Jaycal3 12-11-2012 07:52 AM

Check under the expansion tank itself... thats where my 545 leaked from. its hard to see since its underneath. There is a seem under the tank so if you take your hand and run it along that seem your hand will either get wet or it wont.

dolfan13 12-11-2012 09:01 AM

There's a plastic T behind the throttle body that cracked on mine. It routs coolant between the heads and back to the expansion tank.Very easy,4 bolts throttle body removed cracked hose right there.

praiford 12-12-2012 03:26 AM

Thanks for the great advice. I bought the small plastic tube that sticks into the block. A good catch on the harmonic balance wheel bolts. I remember seeing that on another thread.

Patiopat 12-22-2012 08:38 PM

I just fixed mine and it was behind the throttle body that had to be removed!


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