First off there is a DIY guide for this. See the link below, he did a great job putting this together and is a little better at showing screw locations etc. This is the way i did the install, either way you get the job done is great.
Today I was out running a few errands before I was going to swap cars with a client and then all of a sudden I got the dreaded temperature warning light. Crap. Well I did have all the parts I needed on hand, only a slight inconvenience with having to juggle my schedule around. I tried initiating the water pump bleeding procedure, nothing, and i let the car cool off for about a half hour.
I grabbed the coolant hose and pumped it with my hands for a little bit and then tried the pump bleed again. I heard it working so I nursed it home (under three miles) and quickly got to work. I have an AWD manual, so it's slightly more involved than just a regular 335i to access all the clamps and bolts for the job, but not automatic transmission cooler to mess with either. So it was a little easier than Johnny's car in that regard.
First thing first, get the car elevated with jackstands, or put it up on the lift if you have access to one.
Pull the under tray (lots of screws) and the alumn shield (6 bolts).
Then pull the front brackets for the powersteering lines (2bolts), and coolant hose (3bolts) and drop the sway bar out of the way (4bolts).
Then the passenger front tire (5bolts) and removing the small shield for the powersteering will give some more access (2bolts).
Then remove the two quick disconnect radiator hoses that connect to the thermostat, the temp sensor wire, and then the clamps for the two radiator hoses - access via the tire well. You may need to remove the two bolts holding the thermostat to the water pump and rotate it slightly to gain access to the clamp screws, it all depends how they are clocked and the tools you have on hand.
With the thermostat bolts out you can remove it towards the front bumper and down. This gives room needed to remove the water pump electronic connector via the tire well and then the water pump outlet worm clamp. With this undone, remove the three bolts, the ground wire at the front of the engine and the wire stay on the Web of the water pump. It should slide out towards the front bumper and down.
Installation is the reverse of removal, just pay attention to the clocking of the worm clamps and orientation. Sometimes better access to the clamps is found by putting them in flipped around... sometimes not. The pump goes in with the hose to the thermostat already on and tight, tighten the pump discharge worm clamp after starting the bolts, then final tighten the three bolts. You can reinstall the engine ground and the clamp on the web here as well. Install the wire connector to the pump and then put the thermostat in. Tighten the clamps and install the 2 quick connect hoses.
Some completed shots
Fill with coolant and then bleed the system of air. To bleed the system put the car on a charger, turn the car on but not started, turn the fan speed to 1, and temp all the way up both sides. Hold the gas to the floor for 10 seconds and you should be able to hear the pump run. It's a 12 minute cycle. Top up with coolant until the stick reads 6mm over filled and you should be all set.
With the way I got the pump working again i had a theory about what was failing. I dismantled the water pump to find out. The magnet casing in the middle of the motor had expanded cracking and started coming apart. This was catching on the outer housing the pump, preventing it from spinning.
I broke apart the casing to see how the magnet was contained
Small update to this post... I installed a pretty decent used pump that I had from amother car, only because it was a risk I was willing to take. It lasted two days before my low coolant light came on and found the housing was cracked. I purchased a new pump from bmw (which is a contential brand pump just fyi) and they supplied steel bolts to mount the pump which is new and the pumps went up about 30 dollars in price
.... doing the job twice in the span of 4 days ugh.