Does it use coolant?
Not likely at all that both thermostats are bad. Are you sure you have bled the air out of the engine?
You are pretty much down to (1) radiator plugged or partially plugged (2) internal engine problems, cracked head or block, blown head gasket, etc.
What makes you think its over heating?
As always, that is a really good question... I wish we had a place to do an FAQ about cooling systems. This situation comes up so much it would be a service to the group.
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