Coolant flush questions

[Cubieman]

I have never drained the coolant on my M3 and its time, any tips from those who have done this a few times?
I have a question that may get me laughed at but I need to know the answer.
I see that its a good idea to run the heat on high with the fan on low to get the coolant flowing through the heater core.
My question is, must this be done with the engine running? I watched a video where the guy's first step is to "turn on" the car and set the heat to high and fan to low to open up the system however he does not specify if the engine is running and he does not specify when to shut off the ignition.

Could someone please lay out the steps as far as the ignition/heater core sequence please?
The rest I have somewhat figured out, as how to drain/re-fill, I have one of those vacuum re-fill/purge tools and am anxious to see how that works out.
I have done this job on other vehicles but never did anything with the heater core, I basically just drained the expansion tank/radiator and re-filled/bled. On the M3 I want to be much more thorough and complete on my coolant flush. Thank you.

[WOLFN8TR]

Key on to position 2, engine off.
Heater turned up all the way, fan on low.

[Cubieman]

Thanks.

[bigjae46]

M3 much easier than non-M


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[Cubieman]

So basically...
- ignition pos. 2, heat on high/fan low
- remove thermostat
- remove engine block bolt
- unscrew expansion tank cap
- let drain
- turn of ignition (pos. 2)
- re-insert thermostat/bolt w/ new washer
- ignition pos. 2 heater high/fan low
- fill/bleed air

Sound about right?

Also, I would like to flush the system with distilled water, I assume this simply requires filling the system with distilled water and running for a little while correct? I tend to overcomplicate things.

[heinzboehmer]

I would start the drain with the temp sensor in the lower radiator hose,. Remove that, let everything drain, then completely remove the hose. Then remove the engine block bolt. If you remove the thermostat housing with the system filled you're going to end up with coolant all over the front of your engine. So I would do something like this:

- ignition pos. 2 heater high/fan low
- remove lower rad hose temp sensor
- unscrew expansion tank cap
- let drain until no more comes out
- remove lower hose entirely (this is an absolute pain to do btw)
- let drain
- remove engine block bolt
- let drain
- re-insert temp sensor/hose/bolt w/ new washer
- ignition pos. 2 heater high/fan low
- fill (no need to bleed)
- do the rest of what Tis says (warm up, check, refill, etc)

[Cubieman]

I have heard that removing the lower rad hose is risky as there is a chance for it to potentially break somewhere, is this really the case?

[heinzboehmer]

I've removed mine probably ten times or so without an issue. But I can see how things could be brittle and potentially break if your hoses/o-rings are original.

[Tbonem3]

Our car is self bleeding. After running the engine the first time, check the expansion tank next morning; it'll have likely dropped a bit.

[///m325i]

I have heard that removing the lower rad hose is risky as there is a chance for it to potentially break somewhere, is this really the case?

Removing it is a pain. With the plastic possibly being brittle from all the heat cycles it might crack if you apply too much pressure or start getting frustrated and start yanking at it. I saw a video where someone wedged a long flathead and used it to pry the hose off the radiator so that might work.

[Tbonem3]

Yes, I always use a flat head to help the coolant hoses' plastic fitting get over the o-ring. Only need to leverage them off by about 1/4-5/16", then you can just pull by hand.

[Cubieman]

So is pulling the lower rad hose absolutely necessary to completely flush the coolant?
What if one only removed the thermostat and block bolt then ran distilled water through the system and drained that?
That being said I will try the method of removing the lower rad hose tonight I just really need to take my time so I don't break it from the sounds of it.

[8000RPM]

I also disconnected both hoses to the aux coolant pump then flushed those clean with a hand pump/distilled water. There was more old coolant in there than I thought.

[2004LSB]

Get plenty of buckets ready - - draining the coolant is messy as sh!t! I tried using the Schwaben drain and purge tool and didn't work for me. Had to do it the old fashioned way.

[Cubieman]

So why would you only turn the heat on during filling and not draining? Isn't the idea behind turning the heat on to open up the whole system to be drained (heater core) to maximize the amount of coolant removed.
I am not questioning that is how it is done, that is how I will do it, just curious.