awhile back I replaced my thermostat and did a coolant flush. All seemed fine after the initial maintenance truck heated up heater worked great. After the first trip to work (about 35 min) when I parked and hopped out I did notice a little coolant running from the degas bottle, I chalked it up to an overfill and went on about my day.

Fast forward 2 months (all systems seemed ok)

On the trip home tonight from work I noticed my heater wasn't working and my coolant temperature was climbing, luckily it was cold enough out I was able to limp the truck home and keep the temp down. After I parked I got out and immediately checked under the truck and was greeted by most off my coolant, and it was all coming out of the degas bottle cap. I carefully opened the cap and it burped, pushed some more coolant out and then settled. I felt my top hose and it was cold so I removed the band from the radiator side and pulled the hose back, it was basically a solid column of steam like a choo choo train and it drank down all the fluid in the degas bottle.

additionally I noticed the the line that is supposed to run from the degas bottle to the top passenger side of the radiator and the port on the radiator are both capped. Why would someone cap the circuit from the degas bottle to the radiator?

 

I do have a temp guage, after market and stock and they are both working as I stated it started the climb as I drove down the road. I dont think its the heads, I dont have coolant in the oil and I just had a leakdown test done about 6 months ago. Wouldnt my degas bottle be bubbling if it was a head gasket?

 

In my estimate that says you were EITHER already low on coolant OR the coolant wasn't circulating possibly due to a bad water pump.

This would NOT be due to a bad thermostat BECAUSE the heater would put out a lot of heat because the system is designed to flow the coolant through the heater first before the thermostat opens.