This is the '01 Grand Marquis. The engine, transmission and differential were all rebuilt 12,000 miles ago and every cooling system component is brand new OEM, including a high flow water pump designed for the 4.6L 32-valve found on Lincoln Navigators. The only system that was left untouched was the AC system, which I haven't had any problem with. Also worth mentioning, I am running Steeda underdrive pulleys (crank and water pump only) with a 180 F thermostat and my cooling fan is configured to come on full blast at 206 F. Coolant ratio is 30% G13 to 70% distilled water. A couple of weeks ago I noticed a continuous, fast phased, rapid ticking/clicking noise from the compressor when the AC was on. The ticking went away when the AC was turned off. There were no issues with the AC and pressures were normal at the time. The other thing I noticed was fluctuating rpms at idle. Now I do have custom Stage 2 camshafts, but at idle the rpms will fluctuate up and down like a bad IAC valve, as if the PCM is trying to compensate for something like an air leak to keep the engine running. No vacuum leaks and I threw on a brand new Hitachi IAC valve on there less than 5,000 miles ago. Didn't make a difference between that and the "old" Motorcraft branded Hitachi that was replaced when the engine was out 7,000 miles earlier. No serious heating issues for the first 15 minutes or so of the drive yesterday, but monitoring coolant temperature on my ScanGuage-II, after 30 minutes or so it would go past the 206 F point the fan is supposed to come on full blast. Ambient was 108 F and you could hear the fan running continuously for dear life. It went all the way up to 222 F, unless you turned off the AC, when it slowly started to drop. If you dump it in neutral and rev to about 1,500 rpm, coolant temperature will start to drop, but rarely below 206 F. Even with the AC not running, it'll not drop below 206 F. Driving on the highway, regardless of whether the AC is on or not, you're looking at 211 - 215 F, lowest being 209 F. If the AC is on, it'll hit 218 F and keep climbing until you kill the AC. When the AC is running, it doesn't blow as cold as it used to and I'm thinking there might be a possible leak in the system. The unit was serviced 6 months ago, and there were no leaks or concerns at the time. Regardless, I will check the system pressure. The fins on the radiator and condenser are both squeaky clean. No leaks in the cooling system and coolant is up to level. For experimental reasons, I was thinking about putting the OE water pump pulley to see if it makes a difference, but I have a feeling that may not be the issue. Although I will be checking pressures first, given the ticking noise I was hearing from the compressor, does this sound like a bad compressor clutch that could be dragging down the accessories and causing the overheating? I have heard of clutch pulleys wearing down and causing the compressor to seize and prevent the engine from turning over, but never had it happen to me.