Is it possible to swap thermostats on a 5.9 without removing the alternator and/or a/c compressor?

 

yes. It's a little tricky if you just glance at it, but if you look hard, the water neck just barely clears everything above it.

 

No, you pretty much have to get them out of the way to get to the bolts on the bottom of the housing and to clean the mating surface on the intake.

You don't need to remove the alt and the a/c pump from the bracket and do not disconnect the a/c lines. You can unplug all the wires from the alt. and pump, remove the bolts and pull the whole assembly up and out of the way.

Right up front, the hardest part is gonna be to get the fan and shroud out. I did mine (a 96 5.2) back in Feb. and ended up making a spanner to hold the water pump pulley so that I could loosen the fan. The fan and shroud come out together--then you can get to the lower bolts on the a/c pump/alt. bracket. Really the worst.

You will probably have to remove the idler pulley, too. I lubed the bearings on mine while I had it out.

Let me emphasize, DON'T REMOVE THE REFRIGERANT LINES! You will lose your refrigerant and can contaminate the a/c system--that gets very expensive to clean up and fix.

O'Rielly's and Autozone sell a really nice little cast aluminum replacement thermostat housing, btw. Just in case your old steel one is corroded. Consider replacing radiator and heater hoses while you've got it all apart.

 

is the system different on the 5.2/5.9? I thought they were all on top of the intake? My water neck (3.9) lifted straight up when I removed the 2 bolts holding it down, had no problems getting it out, but it as a tight fit.

 

I changed the thermostat on my 5.2 without removing any of that stuff. It's a little tricky to get the thermostat housing out and back in (you have to tilt it just right), but it fits. And, IIRC, the thermostat had a rubber gasket on it, so there was no scraping old gaskets or anything.