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      02-13-2011, 03:28 AM   #1
santov
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Drives: 2007 Z4 3.0si White over Beige
Join Date: Dec 2010
Location: Bay Area, Calif

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DIY: Best Technique for Coolant Flush

Well I did lots of research and figured out the best way to flush the coolant. My Z4 is only at 25k miles but the fluid was 3 years and 4 months old. According to the TIS manual the process involves one drain and refill. My issue with that is the fluid left in the block isn't flushed out, assuming the stealer does it according to the TIS manual. That leaves almost half of the old fluid still in! I didn't want to mess with the aluminum drain bolt in the block as it's a one-time use bolt and I didn't want to mess with loosening the thermostat hoses.

Even though the fluid may have been good for a few more years, for those of you who believe BMW fluids are "Lifetime", I wanted to flush the fluid to purge any particulate matter and most importantly extend the life waterpump, radiator and thermostat.

Here's my process:

You'll need
2 gallons of BMW OEM fluid (I resarched other brands, but wanted to stick with OEM since it wasn't too much more then generic brands and cheaper than super delux brands).

5 gallons of distilled water. I just got it from WalMart for less than a buck each. Make sure you get distilled not spring or drinking since those have minerals.

8mm socket, T30 Torx, T45 Torx, large flatblade and small phillips screwdrivers.

Drain pan that holds about 3 gallons of fluid.

Papertowels to sop up the giant mess you're about to make. Some SimpleGreen to clean up any coolant splatter.

Since you're going to run the waterpump on battery power only I suggest charging up the battery ahead of time and leaving the charger plugged in.

Setup
Remove the radiator top shroud. Removing the shroud gives you access the vent plug. It's held in place by 8 small plastic plugs with phillips screws in the middle. Unscrew and lift them out. Two T30 metal screws on each side need to come out. There are two large plastic T45 bolts with that serve to hold the top of the radiator in place. You don't need to remove those, but do loosen them a bit.

Lift the car and set down on ramps or jack stands.

Drop the 10 8mm bolts that hold the belly pan up. Move the pan out of the way.

Drain
Remove the resevior cap and loosen the vent screw. You might hear some hissing.

There are two blue plastic drain bolts. One drains the resevior (and drains out a small nipple) the other drains the radiator. Open both up. I propped some cardboard around the drain pan to catch all the splatter. I drained about 1.25 gallons out, leaving about a gallon in the block and hoses.

Refill and vent (burp the air out)
Close the two drain plugs and fill up the resevior to the MAX level with distilled water.

Turn the ignition on (but do NOT start the engine).

Turn heater temp knob all the way to hottest, then set fan to slowest speed (defeat the auto mode and AC). This will open the heater core and thermostat.

Press and hold accelerator pedal all the way down for 10 seconds. This will start the electric water pump's "vent" mode. It will turn off and on for short intervals for about the next 8 minutes.

As soon as the vent screw starts to burp coolant tighten it shut. As the pump turns off and on continue to top off the resevior with fresh water.

Drain the system (1st flush)
Refill w/ distilled water and cycle vent mode
Drain the system (2nd flush)

Last Refill and Vent
Lastly refill with BMW OEM Coolant. Since there's still about a gallon of lightly diluted water in the block I added 2 quarts of 100% coolant, then refill/top off with 50/50 mix.

What I found:
The first drain showed how dark the fluid had become. Even scarier there was a signifigant amount of particulate matter. There wasn't any gritty particles indicating tap water, but thin ribbons of rubber and a few sand sized rubber particles, hopefully break-in material from all the rubber hoses. Getting this junk out is the best way of extending the life of cooling system components. The second flush still had some rubber particles in it. The last flush was pretty clean and when I losened the drain plugs the coolant came gushing out instead of dribbling out.

Here's a pic showing the differences in the various stages of flushes:



Finish up:

Spray some diluted SimpleGreen on anything the coolant got on, dried coolant attracts dirt. Clean up any spilled coolant to keep kids and pets safe.

Make sure the two drain plugs and vent bolt are snug. Reinstall top shroud and belly pan. Set the car back down on the ground.

Start it up and look for leaks, then go for a test ride. I noticed my coolant needle runs around 11:45 instead of 12:30. More importantly I've got clean fluid in my block!

Last edited by santov; 02-13-2011 at 06:20 PM..
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