For whatever reason, I can't see a full-sized pic... its friggin tiny. (less than an inch square...)

 

**** if it's cold enough up in Michigan at the moment you may not even need a fan

 

It's quite possible the fan clutch was /is part of the problem . Replace it too.

 

Fascinating, I am having almost exactly the same issues. I have had to deal with an overheating car a couple of years ago that I spent about 27 hours on until I figured out all of the issues so I bought my 96 5.9 knowing it had an overheating issue just like yours for a good deal thinking I could handle whatever the problem was.

I figured out that the owner before the last one had put a bunch of head gasket repair or stop leak of some type because I can see there are a bunch of particles in the coolant even after the last owner back flushed the system for an hour. There was no heat coming out of the vents and then I figured out after I replaced the water pump that if I revved the engine up to 3k a couple of times real quick that the vents started blowing warm air really quick. So that means the heater core was clogged with all of that stop leak stuff. I have been pulling it off of the radiator cap where it is collecting every so often.

I also found out why the stop leak was put in there. At some point someone broke one of the bolts holding the thermostat neck on and drilled and tapped it a size larger. Unfortunately some moron stuck a bolt that was a little too long causing a leak, causing the overheating. So I honestly could have fixed this by just replacing the thermostat gasket and a few washers or a correctly sized bolt but now I am having to switch to an electric fan setup because I also cannot get my old water pump separated from the fan and clutch assembly.

I have confirmed multiple times that mine is not a head gasket leak because I used the loan a tool program at my local autoparts store and got a block tester and the fluid. I also got a pressure tester kit to confirm that the cap was good and found the leak because of the pressure testing kit. To the OP I recommend saving yourself a lot of hassle and wondering and getting both of these from your local autoparts store, they will likely have a loan a tool program that you can use and prevent any further frustration. I would just go electric like I am for the fan at $70 it is worth it to not have to deal with the clutch fan and may help save a little gas in the long run.

~Spike~

 

This is the first time Ive read this thread. You should of back flushed the whole system . clogged heater cores can cause all kinds off cooling system performance issues. when freeze plugs go bad they put enough" rust" in system to clogg stuff. Back flushing the heater core would have been the easiest and cheapest. i would go electric fan all the way.

 

Pop the water pump out and check the blades