Ian, I agree with Longbox. It sounds like you were OK until you changed the thermostat. The temps with the 180 is perfectly normal. Even the temp gauge could be off a few degree's.
(sounds like the 160 thermostat is a dud or upside down)

For now, I'd put the 180 back in and monitor the temp as you were doing. If it remains the same as you mentioned then I think your good to go. A couple things you may want to check is to make sure your fan belt is tight and not slipping on the new water pump and be sure your radiator cap is appropriate for the radiator your using.
.... or you using coolant/antifreeze, or have you just been running plain water during your test runs. If using plain water then switch to coolant

...another thought that comes to mind is the heater core. Is it clean or did some trash from it get into the radiator...or perhaps you have it by-passed?

Hope some of these ideas work for you. Good luck and keep us posted.


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