I swapped out the thermostat this weekend. The job was not too difficult barring the fact that the thermostat is in a place that is hard to reach. In order to make room to work and see, I had to remove the air filter housing all the way to the throttle body and disconnect the tubes and stuff connecting to it. To get an idea of the location, take a look at this link: http://www.justanswer.com/honda/5fzbj-honda-odyssey-location-thermostat-2002-honda-odyssey.html
I disconnected the radiator fan switch cable. Note: if you don't drain the anti-freeze first, some will pour out when you pull the hose connected to the thermostat, and more will come out when you pull the thermostat. I'd advise draining it because I did not and it made a mess but some may still come out after draining. To drain the radiator there is a white colored thumb screw-like piece of plastic on the lower left side (passenger side) of the radiator. It's a pain to get to unless you remove some of that black plastic shroud. I just got some long pliers, pulled the plastic down a little to make some room and was able to get to it. When you loosen this plug the fluid will begin to drain out. Don't take the radiator cap off or you won't get the fluid pulled out of the overflow reservoir. It drains fairly slow.
You can see the top bolt on the thermostat housing, then there is another smaller bolt with some wires connected to it (this bolt is for the wires only, I thought it was the other thermostat housing bolt). The other thermostat housing bolt, you can't see from the top, but you can feel it, it's on the other side from first bolt. I had to get some small sockets and such with various size extenders to get them off, was difficult due to access. When the housing bolts are off, the housing will pull off. After pulling the housing off, look at the thermostat, the air-hole with a piece of metal hanging out it, is at the top, the new one needs to go in the same way. Also, near the top, the rubber seal around the stat has a piece of rubber protruding that seats into the metal where the stat goes. The new stat had the rubber seal with the protruding piece but it was positioned wrong, so I had to remove the rubber from the new stat and reposition it, fairly easy. Seat the new stat in place, and put the housing on, and bolt it back in. Put everything back together. No special procedures, just refill fluid and all was well. If you have any questions, let me know.
I disconnected the radiator fan switch cable. Note: if you don't drain the anti-freeze first, some will pour out when you pull the hose connected to the thermostat, and more will come out when you pull the thermostat. I'd advise draining it because I did not and it made a mess but some may still come out after draining. To drain the radiator there is a white colored thumb screw-like piece of plastic on the lower left side (passenger side) of the radiator. It's a pain to get to unless you remove some of that black plastic shroud. I just got some long pliers, pulled the plastic down a little to make some room and was able to get to it. When you loosen this plug the fluid will begin to drain out. Don't take the radiator cap off or you won't get the fluid pulled out of the overflow reservoir. It drains fairly slow.
You can see the top bolt on the thermostat housing, then there is another smaller bolt with some wires connected to it (this bolt is for the wires only, I thought it was the other thermostat housing bolt). The other thermostat housing bolt, you can't see from the top, but you can feel it, it's on the other side from first bolt. I had to get some small sockets and such with various size extenders to get them off, was difficult due to access. When the housing bolts are off, the housing will pull off. After pulling the housing off, look at the thermostat, the air-hole with a piece of metal hanging out it, is at the top, the new one needs to go in the same way. Also, near the top, the rubber seal around the stat has a piece of rubber protruding that seats into the metal where the stat goes. The new stat had the rubber seal with the protruding piece but it was positioned wrong, so I had to remove the rubber from the new stat and reposition it, fairly easy. Seat the new stat in place, and put the housing on, and bolt it back in. Put everything back together. No special procedures, just refill fluid and all was well. If you have any questions, let me know.