Procedure to Drain, Flush, and Refill Coolant (1989 325i Cabrio, M20, B25)

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This procedure will help get your e30 M20 engine ready for summer.

Fluids, Parts and Tools Required
2 - gallons of BMW Coolant 82-14-1-467-704 ($25 each)
1 - 12 oz bottle of Redline Water Wetter additive ($8)
6 - gallons of distilled water ($1.50 each)
1 - plug for engine block 07-11-9-919-228 ($1.50)
1 - 14x18 mm aluminum plug seal ring 07-11-9-963-200 ($0.50)
1 - plastic plug for radiator 17-11-1-468-467 or 17-11-1-719-384 ($6)
1 - 10 gallon plastic tub preferably 8”D x 20”L x 15”W
1 - empty clean 1 gallon plastic water or milk jug
2 - “Rhino” ramps (better than jack stands as you’ll get the car higher off the floor)
Liquid Wrench spray penetrant
Tube of Lubro Moly Anti-Seize compound #LM 508 (for engine drain plug only).
8 mm socket
13 mm socket
19 mm socket
Torque wrench (for engine drain plug only)
6” funnel
Old bath towels and maybe a roll of paper towels
Garden hose with spray nozzle
Safety eye glasses
A couple pairs of disposable latex gloves

Spray ”Liquid Wrench” or an equivalent penetrant the evening prior to the bleed screw on top of the T-stat housing and on the engine block plug.
Use “Rhino” ramps to raise front end and check that plastic tub will clear.
Engine is to be cool to the touch.
Put on, and keep on, your safety glasses.
Have garden hose sprayer ready on the side to wash down contaminated surfaces including you.
Cab temperature control should be set all the way to Hot and fan switch on low (#1) speed.
Turn ignition to on, don’t start engine (this will aid in draining the heater core).
Remove cap from expansion tank and keep close by.
Place drain tub under driver side of radiator.
Remove black plastic radiator drain plug (13 mm) and drain radiator coolant.
After a few seconds or so loosen the bleed screw. If coolant comes out wait a few more seconds.
When it’s down to just a drip replace the big tub with a smaller container (plastic coffee jar).
Leave the radiator drain plug off.
Locate the engine block drain plug on the passenger side of the block.
Center the drain tub under it and offset a little towards the outboard side.
Reach down from above and remove block drain plug (19 mm) and drain engine block coolant adjusting the tub location to catch as much as possible.
When down to just a drip turn fan and ignition off.
Set drain tub off to the side until ready to transfer old coolant into empty jugs.
Run 4 gallons of distilled water through expansion tank until runs clear out of engine block (you shouldn’t see any draining out of radiator).
Apply a tiny dab of anti-seize compound to the threads of the engine block plug.
Replace engine block plug with aluminum seal ring and torque to 35 N-M (26 ft-lbs).
Replace plastic radiator drain plug (without anti-seize) tight but don’t crank on it as you’ll snap it.
Leave the bleed screw open.

Mix up 3 gallons (12 quarts) of 50% coolant and 50% distilled water mix.
Use 2 empty plastic jugs for the first 2 gallons and an empty BMW jug for the 3rd as when all is said and done here you will have filled the system with just under 10 quarts and you can save the last +/-2 quarts for future maintenance purposes.
Don’t mix the Redline Water Wetter with the coolant/distilled water mix as you’ll want to add all 12 oz in one shot.
Turn the ignition to on and the fan on #1 speed (this will aid in filling the heater core).
With the funnel in the expansion tank start filling the system very very slowly to avoid creating air pockets.
You’ll probably get at least 2 gallons in before you hit the mark in the expansion tank or you see coolant bleeding out the bleed screw (which ever comes first).
Pour in the entire bottle of Redline after the first gallon of mix.
If you see bleeding before you hit the tank mark then close the bleed screw (not torqued) and wash down around it with the garden hose.
Start the engine and hold throttle at +/- 1500 RPM until T-stat opens (temp gauge should be just under the 12:00 position).
You’ll know the T-stat has opened as you’ll notice the expansion tank level will suddenly drop as the coolant is now allowed to enter the radiator.
Open the bleed screw and continue filling expansion tank until you hit the mark in the tank or you see coolant and most likely air bubbles bleeding from the bleed screw (which ever comes first).
You’ll probably get another 1 ½ quarts in the system at this stage for a total of 9 ½ .
Assuming you see sputtering from the bleed screw before you hit the tank mark then continue to bleed air out until the bubbles stop.
While you’re watching the bleed screw you need to watch the tank as well. If you see the level beginning to rise higher than the mark then quickly put the cap on hand tight.
Close the bleed screw (not torqued) and wash down around it with the garden hose.
Turn engine and ignition to off.
Check the level in the tank and top off to the mark.
Take a break and allow the engine to totally cool down.
Re-check the level in the tank and top off to the mark.
Start the engine and hold throttle at +/- 1500 RPM and repeat the same steps again.
You’ll probably only have to add less than a quart this time.
Close the bleed screw tight but don’t crank on it or torque it as you’ll snap it.
Close the expansion tank cap.
Take a 20 mile tour of your town or city in city traffic with the BMW jug of remaining mix and your 8 mm socket and ratchet.
Watch the temperature gauge that it doesn’t creep higher than 12:00. If for some reason it does it’s because you’ve got poor circulation caused by air pockets and cavitation.
Find a safe place to pull over and park so you can bleed again and top off to the mark.
Finish your tour and head home.
The next morning check the level in the expansion tank and top off as necessary to the cold mark (you might need to add the last quart or less).
Put the BMW jug of remaining (+/- ½ gallon) mix upright in your trunk or behind your seat for a few weeks as a precaution only as the weather and driving conditions may be more extreme (hotter) compared to your 20 mile trial tour.

That’s it. Happy motoring and “keep the greasy side down”.

Article written by a long lost member - 89Cabreeo

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