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      02-13-2011, 04:28 AM   #1
santov
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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 07:20 PM.
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      02-13-2011, 05:15 AM   #2
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very cool, im sure i will attempt this in the future. thanks for the write up, seems pretty complete
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      02-13-2011, 01:17 PM   #3
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Thank you so much for a very detailed DIY! One quick question, at which step did you use the distilled water? I only noticed you used "plain water" in step 3! Thanks
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      02-13-2011, 07:28 PM   #4
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Quote:
Originally Posted by Pheonix View Post
Thank you so much for a very detailed DIY! One quick question, at which step did you use the distilled water? I only noticed you used "plain water" in step 3! Thanks
Thanks for catching that, I fixed the directions. Yes, use only distilled water to "flush" the old coolant. Each time you do it the concentration of old coolant decreases (and you purge more debris).
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      02-14-2011, 07:48 AM   #5
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Nice write up - I've been wondering about this too so it's great to see some one dig into it. Mines a September '06 build with just under 25K and the age of the coolant more than the miles is my concern as well. This is definitely on my spring to-do list.

Do you think this procedure would be the same on a Z4M?

Just to add to the type of water questions - as santov said, use only distilled water, even for flushing. You do not want to add tap water at any time because you'll probably never get it all out and it may contain increased mineral content, which will vary depending on where you live. Just buy plenty of distilled, it's cheap and not like you're going to be doing coolant flushes that often.
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      02-17-2011, 12:52 AM   #6
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Quote:
Originally Posted by onebluemcm View Post
Do you think this procedure would be the same on a Z4M?
I looked in TIS and I didn't realize that the //M S54 engine does not have a electric water pump so there's no "vent" mode for the cooling system.


Here's the TIS procedure for venting the S54. You'll have to do this between the flushes.

Quote:
Originally Posted by BMWTIS
Open vent screw.
Perform filling operation slowly.
Close vent screw when bubble-free coolant emerges.
Top up coolant expansion tank up to maximum cold fill level.
Close expansion tank.
Run engine up to operating temperature until the thermostat opens.
Allow car to cool down until coolant temperature drops below 30C.
Open sealing cap on expansion tank slowly in order to gradually reduce residual pressure.
Top up coolant expansion tank up to maximum cold fill level.
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      02-17-2011, 07:21 AM   #7
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Thanks. Yeah, I thought it was belt driven as well but hadn't taken the time to 100% confirm, so thanks for the answer! I think it may be harder, more time consuming and possibly more materials-consuming, to get a near 100% flush on the S54.
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      02-24-2011, 06:41 PM   #8
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Well, as a result of your excellent write-up I'm going to try this myself I think. My only question is whether my 2005 2.5i has the electric water pump with "vent mode." Anyone know where I can find out about that?
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      02-24-2011, 08:14 PM   #9
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Quote:
Originally Posted by plblair View Post
Well, as a result of your excellent write-up I'm going to try this myself I think. My only question is whether my 2005 2.5i has the electric water pump with "vent mode." Anyone know where I can find out about that?
I looked in TIS and a 2005 roadster has either M54 or N52 engine. If you have the N52 engine you have the electric waterpump. If you have the M54 you have the belt water pump and get to do the above steps to "flush".

If you want PM me your last 7 digits of the VIN and I can confirm in TIS.
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      02-24-2011, 08:17 PM   #10
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Nice write up. The debris you found is certainly something to think about. That can't be good for the pump.
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      02-26-2011, 12:00 AM   #11
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For those of you with the M54 engine (2.5 and pre 2006 I think) here's the TIS how-to.
Attached Images
File Type: pdf M54_Draining.pdf (124.3 KB, 928 views)
File Type: pdf M54_Venting.pdf (86.7 KB, 644 views)
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      03-07-2011, 05:56 PM   #12
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Thank you for the PDF for the M54. I have to replace the expansion tank, and this will help me get started (and finished). Might as well do the flush as well while I'm in there.
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      03-10-2011, 07:48 PM   #13
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santov thanks as well. Will attempt this in the spring.
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      09-15-2011, 12:00 PM   #14
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Car has 98k miles on it. Looks like I'll be doing mine soon
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      11-23-2011, 11:40 AM   #15
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Is there no block drain? Or is it unnecessary when flushing the radiator/block if you flush it as described above?
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      11-23-2011, 12:58 PM   #16
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2003-2005 = M54 pre facelift

2006-2008 = N52 post facelift
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      11-27-2011, 08:55 PM   #17
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Quote:
Originally Posted by BMW Maniac View Post
Is there no block drain? Or is it unnecessary when flushing the radiator/block if you flush it as described above?
There is a block drain...

No touchy! The aluminum bolt is one time use and the threads in a older block can be brittle.

Doing flushes in this DIY are plenty to get the junk out.

Good luck!
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      11-28-2011, 12:49 PM   #18
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Quote:
Originally Posted by santov View Post
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.
Thank goodness for TIS and your write-up. I don't think anyone would've stumbled upon that process otherwise.
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      03-12-2012, 09:26 PM   #19
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Thanks for the DIY.
It's on my to do list this spring.
If I come across anything else S54 specific, I'll add to this.
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      03-12-2012, 09:37 PM   #20
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Quote:
Originally Posted by inTgr8r View Post
Thanks for the DIY.
It's on my to do list this spring.
If I come across anything else S54 specific, I'll add to this.
Santov, great DIY and thank you. inTgr8r, sounds great. This is on my list to do as well but I'm more than willing to follow in your footsteps!
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      03-13-2012, 06:51 AM   #21
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Found an S54 specific thread by Pal..
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      11-11-2012, 01:49 PM   #22
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thank you so much santov! with your manual it was super easy to flush and refill the coolant

would have never known the trick with the electric water pump. mine was pumping 5 or 6 times in short intervalls on full load and started venting continuously afterwards on like 50% load
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