1. Not to be insulting, but are you sure the thermostat is installed in the correct direction? Don't assume the old one was installed correctly.
2. Do you have a fan clutch? Is it working properly? Should firm up solid with higher temps. If it slips you won't get the air you need.
3. Some engines trap air when you refill them. I didn't see you mention your engine size. Some guys burp the cooling system by jacking up the car a bit at the front and running on idle to force any trapped air out of the system.
4. What is your engine timing? Either way retarded or way advanced can impact temp. Way advanced and cranking on start is usually difficult and pinging when you get into it. Retarded not so obvious except for lower performance. Easy to check with timing light.
5. As @OneofFew said, sometimes a higher temp thermostat is better at slowing down the radiator flow, thus providing more time for cooling the hot coolant. I would do this last.
6. Go to counseling - this problem may drive you nuts.
2. Do you have a fan clutch? Is it working properly? Should firm up solid with higher temps. If it slips you won't get the air you need.
3. Some engines trap air when you refill them. I didn't see you mention your engine size. Some guys burp the cooling system by jacking up the car a bit at the front and running on idle to force any trapped air out of the system.
4. What is your engine timing? Either way retarded or way advanced can impact temp. Way advanced and cranking on start is usually difficult and pinging when you get into it. Retarded not so obvious except for lower performance. Easy to check with timing light.
5. As @OneofFew said, sometimes a higher temp thermostat is better at slowing down the radiator flow, thus providing more time for cooling the hot coolant. I would do this last.
6. Go to counseling - this problem may drive you nuts.