Thermostat location

Here is a guide and the diagrams below so you can see how the job is done:

https://www.2carpros.com/articles/replace-thermostat

Check out the diagrams (below). Please let us know if you need anything else to get the problem fixed.

Cheers

Partially drain the coolant so it is below the thermostat, about half a gallon should do it, then follow the upper radiator hose to the thermostat housing, remove the two bolts, leave the housing attached to the hose, and pull it from the block.
Remove the old thermostat, remove the old gasket install the new one with the spring facing the block, snug the bolts evenly, the housing can and will crack if you do not, refill coolant, and your done!

Mitchell tech line says follow upper hose! Right between the two cams in the center, on top!

Well after all that work, I hope that is it!

Drain the engine coolant into a clean container, so that the level is below the thermostat housing.
If necessary, disconnect the upper radiator hose at the water outlet.
Loosen the securing nuts, then remove the water outlet, gasket, and thermostat from the thermostat housing.

When installing the thermostat, always use a new gasket with sealer and make sure the thermostat spring is facing the inside of the engine. The water outlet housing on VG30i and VG30E engines has the letters UPR and an arrow embossed on the flange edge; they should always be pointing up. The KA24E, VG30i and VG30E engines have a jiggle valve on the thermostat which should always be facing up. Water outlet mounting screws should be tightened to 12-15 ft. Lbs. (16-21 Nm) on all engines but the KA24E, which should be tightened to 5-6 ft. Lbs. (7-8 Nm). Refill and check the coolant level.

What problem are you having with the fuel and temperature gauge? Are they inaccurate, not registering at all, sticking etc.?