car is overheating, no issues to indicate cause

replaced the thermostat, water pump is working. coolant levels ok, but the car continues to overheat. It will get hot on the needle and I'll loose heat. then the car will go back down to normal temps, then heat up again. Any thoughts or ideas?

Is coolant flowing through your radiator? Feel your upper and lower rad hose when the engine is hot to tell.

yes, water is flowing, the hoses get hot

Was the exact same overheating happening before the t-stat was replaced? If so, then did anything else related to the cooling system happen before the t-stat job? Sounds like air in the system, but that wouldn't have happened unless there had been some type of drain and refill.

yes, overheated before and after a new thermostat

Then it would not appear to be air in the system.

Do you have a second gen with the electronically controlled t-stat? If so, then maybe the ecu to opening and closing the t-stat, which would explain what you're seeing. No idea how that could happen however.

Check your oil. Is it full of moisture or coolant? If yes, you have a head gasket problem.

But being that you said your coolant temp level spikes and then comes back down to normal temp, and spikes again, it might be that your thermostat is defective and opening itself and too high of a temperature.

Brand new thermostat in the car. Also, now it developed a misfire P0304 and I just put in new plugs too. It's blowing a lot of white smoke out of the exhaust as well. When idling, it's fine. Drove it around temps went from about 188 to 230 in a very short time period. Heat stops working when the engine temp rises.

Well that's become quite a bit different than your OP, and it now seems much more likely the problem is a blown HG, and getting worse over time. It's possible the original problem was the t-stat stuck closed, which caused the first overheat and blew the HG. I'd recommend doing a leak down test, and check to see if any bubbles show up in the coolant. Or a combustion gas chemical test would confirm the bad HG as well.

yeah, that's what i'm afraid of