Flushed Cooling System, Now Issues

2002 ES 4 cyl. ~125K

Just flushed the cooling system and I noticed after this mornings paper delivery that the lower hose was cool to touch after about 2.5 hours of hard, stop and go driving. The temp gauge never went past half way so, unless my temp. sensor is bad, the engine wasn't overheating.

I just started engine with radiator cap off to see if any bubbles or air would release once thermostat opened, but no luck. (Again, temp gauge never shows any danger of overheating, if it can be trusted.) I also cannot be certain the thermostat actually opened. I didn't see a rush of air push fluid out of radiator, or see it quickly drop its level, just sort of stayed the same after about 15-20 minutes of idling and revving to ~3K RPM.

As I'm squeezing the hoses, its clear the top hose is full of fluid (and hot) but the lower hose feels empty, filled with air, and cool. I think I have some sort of restriction that isnt allowing fluid to pass thru the thermostat into the lower hose or thermostat itself is bad?

When I did flush I removed the thermostat, toggled heat setting on high, and flushed with water for about 5 minutes. I didn't notice any discolor or rust/sediment draining from radiator. I reinstalled thermostat (what I thought was toggle valve straight up, but am now second guessing) and refilled with fluid.

Now I'm at a standstill, not really sure where to start? I guess removing the thermostat and checking proper function is 1st? Would re-installing the thermostat with the toggle valve not perfectly straight up cause this issue? Any sure-fire ways to purge air from the system?

Any help, advice is greatly appreciated!

patience. put a funnel on the radiator and watch the level as it idles. i dont like to rev it up and hold it at certain rpm when i burp the coolant system. make sure to fill the funnel up with coolant and put a mark on the level. if you watch you should see some bubbles coming up. see if you can find, borrow or buy an infrared laser thermometer and shoot the thermostat housing. around the temp of the themostat you purchased (oem is 190ish). when the temp gets near 190 the level in the funnel should drop. make sure to use a 50/50 mix of coolant, some manufacturers wont say concentrated needs to be diluted. remember, oem specification for coolant capacity is 7.4 quarts so just shy of 2 gallons. also make sure your fans are coming on, thats a way of telling you your temp sensor is working correctly.