Unfortunately, you're probably well out of the parameters of any lender who'd give you a decent rate on a refi.
Most lenders who do refi limit it to 5-6 years old and/or under 100,000 miles.
The general lifespan (for depreciation/accounting purposes) of a fixed asset like a car is 5 years, and it is generally considered that any personal vehicle (as opposed to a commercial truck) has a lifespan of 120,000 miles. This is the figure used to calculate damages or value when you're dealing with vehicles in lemon law suits or other claims like that.
Unfortunately, yours is well outside those limits.
You may find someone willing to refi it, but I would expect that to be a not-so-reputable lender who may have all kinds of fantastic fees and interest rates. I feel for you, because grad school is demanding both financially and time-wise, but I don't think a basic refi for the purposes of lowering your interest is really in the cards.
