Sounds like you speak from experience. How did it happen?
I had a Dodge Dynasty that regularly had it's (insanely huge) trunk filled with lots of stuff - college moves, mostly. Eventually, I had to get the rear dead axle welded up, because the suspension mount tabs were tearing off.
Basically, I'm arguing that if you're going to run a vehicle radically above it's GVWR, you should know what you're doing, and "because it fits" does not mean you're within GVWR.
A Honda Fit, depending on year and options, has a gap between curb weight and GVWR of 700-900 lbs, and while I can't find a sticker, most cars are rated for front/rear max axle loads as well - and usually not that much on the rear axle.
700 lbs, minus driver, isn't that much firewood. Oak weighs in at around 45 lbs/cu-ft.
The Fit, according to Honda at
http://automobiles.honda.com/fit/specifications.aspx, has:
Cargo Volume — Seat Up: 16.6 cu ft
Cargo Volume — Seat Down: 52.7 cu ft
If you've got 500 lbs of actual payload capacity after driver and 60 lbs of gasoline, that's about 11 cubic feet of wood to fill ti to capacity. Even at a poor 50% packing efficiency, if you've got the seats down, you've got 26 cu ft of wood, or 1170 lbs of wood, plus driver. Whoops. And if you can get the wood crammed in tightly, you can get a lot more in. Tightly packed at 75% efficiency, you're looking at almost 1800 lbs of wood.
Even pine is still 35 lbs/cu ft.
Feel free to run your vehicles radically over gross if you want. It's probably fine. But be aware that you're doing it.
For the OP, it looks like a cord is typically 85-ish cu ft of wood, so you got about 56 cu ft total, in 4 trips, so around 600-700 lbs/trip, depending on the wood. Plus driver & fuel, possibly passenger, it's a good bet you were over GVWR. Almost certainly with 1000 lbs of sand.
Just because it fits does not mean the vehicle can carry it or that it's a good idea.
</private pilot nerding out about weight>
