Rep Power: 0

First timer posting, I know many threads have covered this topic but my issue seems unique. About a month back after driving to work (about 30 miles) I parked and my temp gauge spiked then returned to normal. Checked the coolant levels after the car cooled off and everything was normal. Drove about a week with no issues then stuck in rush hour gauge spiked to 3/4 again and returned, I kept checking the radiator and reservoir and no issues. After reading the threads I replaced the radiator cap and t-stat, drained and refilled the radiator, burped the system twice allowing fans to come on twice with no issues. Everything was fine for a couple weeks and now the gauge is rising again, however this time while cruising at 70 into a head wind on a 50 degree morning. Anytime I return to idle the gauge slowly returns to normal spot about 1/2. After driving the fluid in the reservoir is agitated/bubbling (fluid level does not change). I have full heat/AC when stopped or driving, fans turn on as normal when at idle. When the gauge rises if I turn on the blower only (no heat or AC) the gauge will slowly return to normal once the blower is turned off the gauge rises again. During this whole process the car has never overheated, upper/lower hoses are at same temp. I'm thinking head gasket at this point, would like to know what tests to perform to confirm this. Car is an 05 EX Coupe AT with 148,000 miles. Water pump was changed with timing/accessory belt at 100k. There is no water in oil, no oil in water, coolant does not have exhaust scent. Please advise

 
Rep Power: 186

Blown head gasket. Bubbling in the reservoir is a good tell tail sign. It will eventually get worse and start pushing fluid out the over flow and start emptying the rad. When mine went it took the rad with it. It's good you caught it semi-early. Good luck with it.