How many of these will I need for a complete flush on a 07’ cls550?

1 gallon is enough, this is concentrated and will make 2 gallons of usable coolant once diluted.

How many gallons do I need to buy to complete a flush/ change out the coolant fluid for a 2008 335i convertible v-6, automatic?

1 gal of concentrate would be enough, you would get 2 gal of usable coolant.

Hello! 2018 T6 XC-90. I thought I read something about a “vacuum pump” bring needed to safely flush/change coolant. Is that required, and if so do you have a part number and any helpful video or instructions for this make and model? Thank you.

Vacuum pumps are helpful tools that are used to ensure that there is no air pockets left in the cooling passages after a flush. Something like this would work: CTA-6520 (air compressor is required)

The FCP fitment tab is confirming that this coolant is compatible with my 2017 Volvo XC90 T6, but the back label of the product clearly says Volvo's 1991 - 2014. There has to be a reason they specify this is not for the newer Volvo SPA engines, correct?

The Newer SPA engines use the same blue coolant that is backwards compatible to this antifreeze.

Mercedes c300 4matic sport. Can this be mixed with any/current coolant to top off reservoir? Thanks in advance!

Color dye is dark blue, and can be mixed with all OE HOAT coolants regardless of color.

Just to be sure, is this concentrate or diluted?

Concentrate

Is this the blue or green color? There are three pictures. The main one is green, but the other two are blue so a bit confusing. Thanks.

Color dye is dark blue, and can be mixed with all OE HOAT coolants regardless of color.

Just to confirm. This can be seamlessly mixed with existing BMW coolant?

Correct. Please check the fitment tab for your model.