180 degree F is listed as original equipment spec by most auto supply houses.
The actual factory service manual calls for start to open at 169-176 degree F and open at 194 F. The specification for "full open" is a gap on this unit is > .32 inches.
found at http://www.freeebookpdfmanual.com/car/honda-car/2008-honda-odyssey-owners-manual/ but that 2008
The 1998 Honda Odyssey has the same fuel filter location as the 1996 model seen in the video below.
It is a 4 door vehicle with a rear hatch.
195
at the top of the lower rad hose (in housing)
Follow the upper radiator hose to the engine. The fitting the hose is attached to contains the thermostat.
195 degree
There are two hoses that connect the radiator to the engine block. On older cars, the thermostat would be where the top hose connects - ie where it is easy and convenient to get at, etc. Unfortunately, on your car the thermostat is located where the bottom radiator attaches to the engine block - closer to the firewall, under the breather, etc, where it is a total pain in the ass to get to.
there are two hoses coming from the radiator. the one on the bottom has the thermostat at the end near the back of the engine.
Thermostats range in temperature from 175-205 degrees. Choose a 195 degree thermostat and you'll be fine.
It is located to the left of the thermostat housing for the temperature gauge, there is another to the right of the thermostat housing for the computer.
For 1996 and newer Trouble code P0128 means:Coolant Thermostat (coolant temperature below thermostat regulatin temperature)