Overheating issue, ac and fan clutch?

Hey all,

I own a 2000 Taco, 2.7L 3rz-fe, manual tranny. I replaced the engine back in November after my old engine blew a counterbalance bearing. The engine I put in had about 139K on it. While I was at it, I replaced the clutch, machined the flywheel, got a valve job on the head, replaced the head gasket, water pump, and timing chain. I also replaced all seals and gaskets and flushed the radiator. Truck has been running rock solid since then. With spring coming around, I recently recharged the ac, and it worked great, although I haven't used it much. Two weeks ago, I decided to drive it to Fort Collins, CO, from Salt Lake. I had driven the truck everyday to work, and on a couple trips just an hour or two away from SLC with no problems. About halfway through the journey, I noticed the temp gauge was in the red. I immediately slowed down and cranked the heat, and thank goodness, an auto zone was open in a town only ten miles up the road. My first suspect was the thermostat, as I had foolishly not replaced it when I replaced everything else. I purchased a tstat, coolant, and a coolant temp gauge just for good measure. I gave the temp gauge a change hoping it would be easy, but sure enough, the heat gauge jumped up after ten minutes of driving. So on the side of the road on a Wyoming highway I changed the tstat, refilled the coolant, and burped the system. The truck ran great on the rest of the way to Fort Collins, but on the way back home, the gauge started to creep back up, not into the red or anything, but at about 75-80%. I should note that the wife was driving when it was getting hotter, and she is none too confident or skilled on a stick. As soon as I took over again, the gauge sat right in the middle all the way home. Well, the other day, it was a bit warm, so I turned on the ac. There was no overheating issue, but the next day on the way to work it got really hot again. After work, right in the middle of the gauge again, no issues. I've suspected the ac, just because of the extra load it puts on the engine, and that the problem hasn't appeared until I've started to use it recently. So after work today, I drove it around and couldn't get it to get hot again. But about a minute after I switched on the ac, bam, the temp gauge goes up. There is also a weird, intermittent buzzing sound that comes from the passenger footwell around 1600-2000 rpms, and only lasts for a second. It sounds like a relay struggling to make a connection or something. It also appeared when I started to use the ac again. I looked around and was reading about the fan clutch, and how it should be difficult to manually spin when the engine is hot. I also rolled up a newspaper and put it against the blades when the engine is at idle to see if the fan slows. The fan definitely slows down when the paper is pressed against it, to the point of stopping if I wanted to press hard enough. I can also spin the fan very easily after the engine is off and hot. It seems obvious that the fan clutch is in need of replacing, but I'm curious if you all have any other suggestions, particularly when it comes to the weird sound from the passenger footwell. The temp gauge seems to fluctuate when the overheating issue occurs, and it seems to go down with higher rpms. There are no coolant leaks, and the top hose to the radiator is hot, while the bottom is cold as it should be. I'm hoping to take the truck out of town this weekend on a climbing trip about three hours away, so hopefully it's the fan clutch or something easy. Thoughts?

 

Water pump? If the water pump is is starting to go it could cause the fluctuation in the temperature as the rpm's fluctuate up and down.

 

With the truck at operating temperatures the upper and lower radiator hoses should BOTH be hot. If not then you either have a lot of air trapped in the system or the thermostat isn't opening.

 

X2 on the rad hose temperatures.

Is their not an auxiliary electric fan for when the A/C is in use?