Just buy one more bottle (1.5 litres) and give him all 3.

4.5 litres of MB cooland in an 8.5 Litre system will give you an approximately 53/47 mix of coolant/water. Close enough for the 50/50 mixture you're looking for. Then, buy one more bottle of coolant, save an empty bottle and make up your own 2 litres of 50/50 mixture for your over-flow reservoir and occasional top-offs.

This isn't a science project...it's an everyday thing...

__________________

M. G. Burg
'10 - Dakota SXT - Daily Ride / ≈ 172.5K
.'76 - 450SLC - 107.024.12 / < .89.20 K
..'77 - 280E - 123.033.12 / > 128.20 K
...'67 - El Camino - 283ci / > 207.00 K
....'75 - Yamaha - 650XS / < 21.00 K
.....'87 - G20 Sportvan / > 206.00 K
......'85 - 4WINNS 160 I.O. / 140hp
.......'74 - Honda CT70 / Real 125
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“I didn’t really say everything I said.”
. . . . . . . . . . . . . . . . . . ~ Yogi Berra ~