So, I can't figure this one out. Vehicle is in the title.

This is the backstory, sorry for the long post:

I bought the truck with about 170,000 miles. The previous owner had never once changed the coolant, judging by the condition of it. My heater core was hopelessly clogged, so I replaced it and the thermostat, and flushed the coolant system several times. Since then the heat has worked much better but is still not what I would consider "fully" fixed. It just seems like it should be hotter. It had straight water in it from all the flushing, so yesterday I bought antifreeze to put in it.

I had been driving for close to an hour, and as soon as I got home I shut the truck off and reached under and opened the petcock to drain some water out and add antifreeze. The truck was fully up to temp and the heat was working fine, but the water that drained out of the radiator was ice cold. I opened the overflow bottle and stuck my finger in, the water in it was ice cold as well.

I went ahead and drained some more, poured in the antifreeze and started the truck to try to circulate the antifreeze through it. I let it sit and idle for about 30 minutes. When I went back and shut it off, the overflow bottle was still full of pure antifreeze and was cold. Also, it has not built up pressure in the bottle like it normally does. The temp gauge was right where it always is (maybe 1/3 of the way up), not overheating at all.

I drove to work and back today, about 25 miles, and as soon as I got home I checked the overflow bottle again and it was mixed water and coolant this time, and had built up pressure.

I just can't figure out how after almost an hour of driving the radiator would be that cold and yet the truck not overheating. Thanks for any help and I will answer any more questions you have.

 

Is radiator return hose (upper hose) pressurized ?

Did you check if water pump is working ?
Good luck,

 

I can squeeze the upper hose with it running, but I don't know how pressurized it should be. Should it be too tight to squeeze? I can squeeze on it and hear water gushing into the overflow bottle.

I didn't check the water pump, I guess I assumed if the heat was working it was moving water. Could the impeller be worn down causing low flow maybe?