Gasoline is one of the major 'operating' costs of driving for many people since it costs $0.08 -$0.10/mile
Owning a MBZ for say 15 years and 150,000 miles costs at least $30,000 in depreciation and repair for a per mile cost of $0.20--roughly twice the fuel cost. Insurance costs another $15K for another $0.10 per mile.
Trying to save 8% of $0.08/mi, at best, gets you $0.007 per mile, or maybe $100 a year tops. If that amount of money makes a significant difference to you--sell the car now, you cannot afford it. You will collapse when the cost of 'hard parts' damage comes due.