That's correct; it's on the bottom half of the thermostat housing. To access it you'll have to likely open the thermostat housing and move that top part (you can keep the hoses attached) towards the passenger side of the engine bay. If you're sure the sender is bad, clip the wires and remove the sender with a 19mm socket. When you install the new one, make sure the aluminum sealing washer is on the sender, screw it in place by hand, and then snug it up with a 19mm box or open-end wrench. Finally, attach the wiring connector, and replace the thermostat top housing with a new rubber seal.

BTW, I just bought a new sender from www.fcpgroton.com last week for $30, along with a new reservoir cap ($4), and thermostat and seal ($8).

Regards,

Dean