[BillionPa]

BMW OEM coolant is Zerex G48, same as Saab cars use (blue coolant)

Essentially any blue coolant should be G48, and will work.

I have some pink coolant for newer VW cars here which replaces G48 for use in any VW that called for G48, and should do the same for BMW... but it is even more expensive than BMW coolant, so who cares

[horizon]

You do not need to use "BMW" coolant solely for topping off. The BMW Tech Service Bulletin for "Operating Fluids" specifies:

The cooling system of BMW cars must only be filled with reputable brand name ethylene glycol long-term antifreeze
having corrosion inhibitors that are compatible with aluminum radiators.
Coolants must fulfill four basic requirements.
— Guarantee sufficient cooling.
— Protect various metals (gray cast iron, steel, aluminum alloys, brass, copper and solder) against corrosion.
— Prevent excessive silicate gel precipitation, which may cause clogging of the cooling system.
— Guarantee operation of cooling system in winter (prevent freezing of coolant) and in summer by boosting the boiling
point.

Prestone 50/50 all makes/all models as well as the Peak equivalent meet these specs.

If I was flushing the system, I'd use BMW coolant.

[WapArtist]

Originally Posted by horizon

You do not need to use "BMW" coolant solely for topping off. The BMW Tech Service Bulletin for "Operating Fluids" specifies:

The cooling system of BMW cars must only be filled with reputable brand name ethylene glycol long-term antifreeze
having corrosion inhibitors that are compatible with aluminum radiators.
Coolants must fulfill four basic requirements.
— Guarantee sufficient cooling.
— Protect various metals (gray cast iron, steel, aluminum alloys, brass, copper and solder) against corrosion.
— Prevent excessive silicate gel precipitation, which may cause clogging of the cooling system.
— Guarantee operation of cooling system in winter (prevent freezing of coolant) and in summer by boosting the boiling
point.

Prestone 50/50 all makes/all models as well as the Peak equivalent meet these specs.

If I was flushing the system, I'd use BMW coolant.

Agreed,

I wouldn't want to have a partial flush or any ratio like 60:40 / 50:50 / 70:30 etc. but a top off with Prestone,Peak etc is fine. I probably just added about a cup.

[bimmerzeit]

Would just go with OEM coolant, $20-24 depending where its purchased, mix it up, top it off and done! Keep a mixed gallon in your garage.