I have a Mitsubishi Galant 2003, 2.4L engine with 234k miles on it. When I drive it the temperature gauge gets up to exactly midway, until exactly 30 minutes. Then it goes up to about 2/3 or 3/4 of the way up and then fluctuates between that point and midway after that.

What started all this was that I was seeing the temperature gauge going up and found a small radiator leak and small leaks in my radiator hoses. So I replaced the radiator, coolant temperature sensor, radiator hoses, and the thermostat. 

Ever since I've had the car (I got it with 48k on it) I've never seen the temperature gauge read over the midway mark, until the leak, so I'm assuming it's not normal, even though it's not overheating. 

I've also checked and the coolant level is up all the time and I do hear the radiator fans working. I also "burped" the system twice to ensure there isn't any air pocket causing this, but like I said, the one odd thing is it starts right at 30 minutes.

Any ideas as to what to check for next?

Update:
I've run a vacuum gauge test and it was perfect, no fluctuations and it's within the normal range. No coolant leaks whatsoever, but I'm checking it once a week on the coolant level. No smoke from the tailpipe that I've observed.

So I'm not saying it's not a blown head gasket, but if it is, it has to be a very small leak. I'll check more today.

The problem is still there, but the temperature gauge range is about half of the fluctuations I had seen and now it's returning back to the normal temperature on the gauge or very close. When the car is heating up, both fans are running flat out and then the temperature goes down. 

I did basic voltage/resistance tests on the radiator fan controller and everything was within specs.