How To: BMW M30 Coolant System Flush

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TimU
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How To: BMW M30 Coolant System Flush

Post by TimU »

I wrote this guide because I like checklists and hadn't seen a good step-by-step guide on how to flush the M30 cooling system.
All feedback, updates and advice is welcomed.

How To: BMW M30 Coolant System Flush

The E24 system holds 12L (12.7 qts) of coolant.
At a 50/50 mix that would be 6L of anti-freeze to 6L of distilled water. Coolant and Distilled Water often comes in 5L containers.
In warmer climates, you can dilute to greater than 50/50 if desired. e.g. 5L Coolant to 7L Water will provide no practical difference.

DIY tip:
Get a Radiator flush kit that includes a T-Piece.
Install the T-piece in the hose between the back of the head and the heater valve, located on the RH side of the engine firewall. The block hose runs from the back of the cylinder head to the heater valve (see pic below).
Or DIY a T-Piece with scraps of garden hose.
Install the T-piece to back-flush the system, and then reinstall the OEM hose before filling.

Pro Tip:
Use a coolant flush vacuum kit that keeps the system under pressure, and also force-purges any air.

Flush Instructions:
1. Raise the nose of the car on a hill or jack stands.
2. Loosen the 19mm block drain plug (located between exhaust port #5 & #6) while the engine is cold to avoid burns and difficult angles when hot.
3. [Optional] Add a radiator flush/cleaner additive through the expansion tank.
4. Start the car.
5. Turn the cabin heater temp to FULL to open the heater core valve.
6. Warm the engine to normal operating temp – Approx 10-15mins.
7. Stop the engine.
8. Remove the Block plug to drain coolant.
9. Remove the Radiator screw plug to drain coolant.
10. Back-flush with a garden hose via the T-piece installed to the heater hose.
11. Rinse 4L (4.2qts) of distilled water through the system via the expansion tank and/or heater hose. The goal is to displace as much of the tap water in the block with the distilled water as possible. It is not necessary to get it all out, a little bit of tap water is fine.
12. Reinstall all the drain plugs

Torque specs:
Radiator drain plug: 2-3 Nm (18 to 27 In/lbs)
Engine block drain plug: 50 (+/- 6) Nm (36 (+/- 4) ft/lbs)

Refilling:
13. Open the Bleeder Valve on the T-Stat housing.
14. Fill the radiator first to avoid air locks:
a. Undo and remove the top hose from thermostat housing. Loosen radiator end. Twist hose 90 degrees to vertical to assist filling.
b. Fill radiator with distilled water through this hose. It won’t take much volume.
c. Stop when the bleeder valve starts bubbling.
d. Re-attach hose and fill the rest through the expansion tank.
15. Pour in 6L of undiluted anti-freeze to mix with whatever is already in the block
16. Top off the system with whatever is needed from the remaining 4L of pure distilled water.
17. Close the Bleeder Screw when the air bubbles stop dribbling.
18. The system is 12L and you now have 6L of anti-freeze in it, topping it off with the pure distilled should give about the proper 50/50 mix.
19. Close the bleeder screw
20. Start the engine.
21. Turn the heater temp to “full hot” and bring the engine to normal operating temp.
22. Reopen the Bleeder Screw with the engine idling
23. Close Bleeder Screw when any bubbles stop coming out.

It may take several tries to get fully bled. It helps to have the front raised, or take it out and drive it (don't let it overheat!) or let it sit overnight.

Repeat flush attempts:
1. Engine off, let the coolant settle.
2. Start engine, allow the thermostat to open.
3. With the engine idling, open the Overflow Tank cap (carefully, it may be hot!) and Open the Bleeder Screw
4. Close the Bleeder Screw when bubbles stop coming out.
5. Repeat as needed.
6. Squeeze the large top hose between the radiator and Thermostat house to force any trapped air out the bleeder screw.

If you have any undiluted coolant remaining in the bottles, you can top it up with distilled water to give you a ready 50/50 mix if you wish. Put it on the shelf for topping up the system later.
Make sure you mark it as pre-mixed!
________

Acknowledgements:
* Chris Wight's earlier posts
* Brucey's earlier posts
* Various Youtube videos
Last edited by TimU on Wed Oct 05, 2022 2:12 am, edited 1 time in total.
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Re: How To: BMW M30 Coolant System Flush

Post by hornhospital »

Excellent, step-by-step instructions! Thank you!

One correction. Step #15, undiluted antifreeze is 100% antifreeze, not 50/50. Not a criticism, almost certain that was a typo.
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Ralph in Socal
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Re: How To: BMW M30 Coolant System Flush

Post by Ralph in Socal »

50/50 Zerex GL5 is available at retail outlets Ken. Crazy though as it costs nearly as much as 100%. Distilled water is usually less than $2 a gallon

Not well known is that BMW recommends coolant replacement at 2 year intervals due to the breakdown of corrosion inhibitors

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Re: How To: BMW M30 Coolant System Flush

Post by hornhospital »

I realize that, Ralph. What I was getting at, Tim said:

"Pour in 6L of undiluted 50/50 anti-freeze to mix with whatever is already in the block"

It should read "pour in 6L of undiluted antifreeze"...

The 50/50 stuff is diluted. You should be using full strength, undiluted 100% antifreeze since you are mixing 6L of distilled water in with the 6L antifreeze to result in a 50/50 mix.

On edit: I didn't mean to disrespect an excellent, helpful posting. Only trying to clarify a confusing point (to me, at least).
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TimU
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Re: How To: BMW M30 Coolant System Flush

Post by TimU »

hornhospital wrote: Tue Oct 04, 2022 10:37 pm Excellent, step-by-step instructions! Thank you!

One correction. Step #15, undiluted antifreeze is 100% antifreeze, not 50/50. Not a criticism, almost certain that was a typo.
Thanks Ken, and good pickup on the typo!
Fixed now.
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Re: How To: BMW M30 Coolant System Flush

Post by slfan »

Thank you for the detailed write-up. It will be useful.
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Re: How To: BMW M30 Coolant System Flush

Post by sansouci »

How do you get to the block drains? I'm skinny but can't figure out how.
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Re: How To: BMW M30 Coolant System Flush

Post by GRNSHRK »

2. Loosen the 19mm block drain plug (located between exhaust port #5 & #6) while the engine is cold to avoid burns and difficult angles when hot.
Not easy to get to, but that's where the block drain is :-"
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Re: How To: BMW M30 Coolant System Flush

Post by Slownrusty »

This is really an area where most owners neglect, flushing the cooling system very two years is critical using the blue or pink coolant only, not GO5 and not the cheap green Prestone stuff either.

I shot a video to walk you through how to do this, for those of you who are visual (i know I am).

I hope this helps.

https://www.youtube.com/watch?v=E4Z_cHrdFeA
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Re: How To: BMW M30 Coolant System Flush

Post by silberlingcooper »

does anyone have some pictures of the location of the block plug? and maybe a picture of where the T piece will connect to on back of block and heater valve hose? i do not see any picture listed on the post.
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Re: How To: BMW M30 Coolant System Flush

Post by Ralph in Socal »

M30 block plug viewed from underneath. This is in an e34 but same location for all M30. Passenger side, under the exhaust manifold, just in front of the block flange for the transmission. 19 mm head

Ralph
20231031_123757.jpg
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Re: How To: BMW M30 Coolant System Flush

Post by silberlingcooper »

Ralph in Socal wrote: Wed Nov 01, 2023 8:08 am M30 block plug viewed from underneath. This is in an e34 but same location for all M30. Passenger side, under the exhaust manifold, just in front of the block flange for the transmission. 19 mm head

Ralph
20231031_123757.jpg

thankyou! i am overhauling my cooling system currently as sitting 20 years has taken a toll. after finally getting it running its going right back to being taken apart. every hose, thermo, water pump, etc.. new hardware for every bolt being taken off and going to perform a flush after. Hopefully not missing anything
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