Wraith

My Accord just crossed 160K on a four hour drive and toward the middle of the drive, she started to sputter a bit at around 3000 rpms as I was giving it gas (one quick hitch then business as usual). She started to do this more frequently when I was giving it any gas at all and thankfully I'd just made it home. I took a look under the hood and had dropped about half my oil capacity (I also checked before I started out and she was fine). Then I remembered that people on the highway were flashing their lights at me so I may have been smoking, but I didn't smell anything, nor did I notice the engine temperature rise. I didn't see any oil pooling/dripping from the under the oil pan drainage bolt or the car in general.

I'd just changed the oil about 3 weeks ago, but I also commute a ways every day, so I'd put on about 2.5K since then. I use SAE 5-W30 as that's what the manual said, but I'm unsure if I should be using a heavier oil given the mileage on the car.

This is the first engine trouble I've had with this car thus far, but I bought it used and I'm pretty sure the previous owner barely took care of her.

Any suggestions on the cause or oil weight I should be using?