So this weekend I spent most of my waking hours doing a cooling overhaul of my '04 545i. This began as a simple plan to replace the water pump, as I have about 110k miles and the water pump was believed to be original. (As it turns out, it was original and the impeller was in surprisingly good shape,)

The project grew as I realized the hoses and belts should also be replaced. I ended up replacing the five hoses that are accessible in the front engine bay, the water pump, both the AC and accessory belts, the belt tensioner, deflection pulley, and the water pump pulley. I would recommend replacing your thermostat, unless it's newer like mine was.

Here are some of my lessons learned and tips that may help others:

-The lower water pump bolt CAN be removed without removing the main vibration damper. See Tg2k's post in this thread:
545i N62 Water Pump/Pulley Replacement DIY - Bimmerfest - BMW Forums

1) In order to replace the hose that runs from the expansion tank and behind the main air pipe, the throttle unit must be removed. This removal is not hard, but replace the gasket while you are in there (I did not, because I didn't know I was going to encounter it and didn't want to wait for one). This particular coolant hose is tedious, but not complicated.

2) However, be careful in that area. The crankcase vent tubes are here and the original ones are very brittle. This is a great time to replace these. I again, did not foresee this, so I did not replace them.

3) While replacing all of my hoses, I noticed a lot of crap built up (mostly leaves) between the main radiator and intermediate radiator (transmission/steering cooler?) At this point, I just pulled the radiator out and vacuumed it, since the fan and hoses were already removed. This is highly advised. This is also a good time to inspect your radiator in general.

4) When putting the AC belt on, I made healthservices' special tool, which can be made if you own a hacksaw and can get a package of fluid clamps from Harbor Freight. I've seen threads about others adding a tensioner to their N62 blocks, but the expense seems overkill for something you might replace once in the life of the car. See link: https://5series.net/forums/e60-discu...-124830/page2/
(Many thanks to healthservices, I owe him a beer)

5) If you replace the lower hose from the radiator to the water pump, plan on putting in a new coolant temp sensor (also called the auxillary fan switch). Mine was only 18 months old from my thermostat replacement, but it's very difficult to remove intact. Mine broke into about five pieces. It's essentially a one time use item. Naturally I did not plan for this and had to run to New Country to secure one before they closed. It's a commonly stocked part since many different engines use it.

6) Make sure you have all the tools you need. This may sound obvious, but I forgot to purchase a 27mm socket for the main crank bolt, a T60 socket for the tensioner pulley, and a T50 for the deflection pulley.

7) Have an extra hose clamp on hand (about 1/2") for the coolant pipe that runs across the top of the radiator from the expansion tank to the top driver's side of the radiator. This has one of those weird pinch clips that doesn't like to be reused.

Given the $700 or so I spent on parts, I'm guessing I saved a whole chunk of money on labor. I wouldn't have been able to do it without this forum.

 

Excellent.
In the process, you've learned a lot more about your car.

 

Very eye opening. Especially all of the oil everywhere