Translating notes: bad customer feedback II

In a recent text, one of my translator colleagues did the client the favor of stating the European "liters per 100 kilometers" as miles per gallon, thus: "1.38 liters per 100 kilometers (170+ miles per US gallon)". This information is especially helpful for English readers because the figures are quite different: the better gas consumption, the lower the L/100 km figure is, whereas your mpg figure gets higher as fuel consumption becomes more efficient.

Nonetheless, I got this from the (German) client:

Put "Roughly 0.6 gallon [sic] per 100 miles" to keep the counting the same and not cause confusion."