2002 Toyota Avalon

Engine Performance problem
2002 Toyota Avalon 6 cyl Front Wheel Drive Manual 53,000 miles

engine light came on and my brother disconnected new battery and light went out. Two weeks later
it's back on again. Took to auto zone and computer said it was engine coolant-or thermostat.
. Went out in morning. Started and engine light on
again. Looked under hood and fan was running fine.
I will say that the car does sit for a few days before I drive it sometimes. Not sure if it's a clogged radiator hose or the engine isn't getting it's coolant. But the engine was cold. And the light still came on. Any iideas?
Julia schultz
April 7, 2008.

If you could post the code, it would help in the diagnosis.

Apr 7, 2008.
Julie again. Couldn't remember the code from
auto zone computer. But did find out it WAS the
thermostat and it wasn't creating an overheating
potential. The opposit. It wasn't regulating the
coolant correctly. Had thermostat replaced and
it was 90.00.

Julia schultz
Apr 10, 2008.