Radiator or Thermostat???

While driving uphill with the AC on, my temp gauge pegs out. Turn the AC off, and the temp cools down. While drving on a flat road with the AC on, it's fine. About a year ago I had the radiator flushed and filled and I know this doesn't totally clean it out. So.... could it be one or the other or both?

I appreciate the input.

Also, is there a high flow radiator that may fit the VX?

Thanks in advance.

Radiator - make sure the fins are clean front and rear - clean with garden hose from the inside out. If it started after the flush, then it is probably clogged inside and will need to be cleaned or replaced.

Is the coolant / water mix correct? You might want to drain and refill according to instructions on container.

Coolant/Water mix is correct (recently checked). This happend once before, then I flushed/filled it and it worked fine ( a year ago) and now it's happening again, so.... gonna call it a radiator and get it fixed.

Thanks Tone