08 M3 coolant job - only filled less than 1gal/4qts?

Hey all, drained my coolant on my 2008 M3 via radiator reservoir, reinstalled that screw, and refilled with my 50/50 mix of bmw genuine coolant and distilled water. Bled system via the expansion tank bleed screw 3-4 times before topping off to max line.

I was only able to drain about 1gal/4qts initially via the reservoir screw, thus being able to only fill the same 1gal/4qts of my new 50/50 mix. Apparently S65s should have around 2.5-3gal/10-12qts of coolant capacity.

Is it normal i was only able to drain out and thus fill a third of that capacity?

TIA

Totally normal to only fill the expansion tank about a gallon. You don’t just drain the expansion tank. There are DIY guides on this site if you look for them.

spammysammich wrote

Totally normal to only fill the expansion tank about a gallon. You don’t just drain the expansion tank. There are DIY guides on this site if you look for them.

Followed them and only drained radiator, then bled 3 times before topping off. AFAIK the only place to drain coolant on the S65 is via reservoir since draining the block is an entirely difficult/unnecesary process?

Yeah I don’t want to pull those plugs either. I’m considering pulling the thermostat, reassembling the housing and trying to gravity flush by dumping three gallons of distilled water through a suspended funnel/hose into the expansion tank. Then run the car with the lower radiator drain out until it’s fully flushed.

I asked a couple bmw mechanics how they do a full flush and they both said they use a vacuum fill. But neither of them shot down my shade tree mechanic nonsense so maaaaybe it’ll work? Or maybe I’ll just buck up and wait until I get a compressor and vac fill system? Looking back through the DIY section, pulling the plugs looks to be a major pain in the dick to clean up after.

spammysammich wrote

Yeah I don’t want to pull those plugs either. I’m considering pulling the thermostat, reassembling the housing and trying to gravity flush by dumping three gallons of distilled water through a suspended funnel/hose into the expansion tank. Then run the car with the lower radiator drain out until it’s fully flushed.

I asked a couple bmw mechanics how they do a full flush and they both said they use a vacuum fill. But neither of them shot down my shade tree mechanic nonsense so maaaaybe it’ll work? Or maybe I’ll just buck up and wait until I get a compressor and vac fill system? Looking back through the DIY section, pulling the plugs looks to be a major pain in the dick to clean up after.

Gotcha. Thanks for the advice, given that BMW calls it a "lifetime fluid" I'll just top off in the coming days when I drive it and call it a day.