The only time the lower hose will get sucked closed is when the RPM it up, not at idle.
So if you were inside watching the gauge with the RPM up to say 2000 and the temp got up high and you then got out to check the lower hose it would not be closed as it is at idle.
If you can look at the hose and raise the RPM or have someone do it for you and I bet with out the spring it will close.

If it is pulling coolant in from the reservoir then there still had to be air in the system.
Did you bring the RPM up with the cap off? I keep it off and bring the RPM up & down a few times as it will change the coolant flow rate and help push the air out.
Dave ----

 

So far we've only had you check the easy stuff in hopes of an easy fix. I'd say it's time to dig a bit deeper.

Definitely take care of that missing spring in the lower radiator hose. As Dave said, that's usually only a problem at higher RPM but you should still fix that.

Do you know any recent history of this truck, such as recent repair work or why it was parked? Those can be big clues.

Do a pressure test of the cooling system. If you don't have a tester, some parts stores loan tools for free. Pump up the system to the rating on the cap and make sure it will hold for at least 15 minutes. If not, there's a leak somewhere that needs attention. If a leak is preventing normal pressure buildup, the coolant will boil at a lower temperature.

Pressure test the cap, too.

Next is to test for exhaust in the cooling system. The tester looks like a turkey baster and holds a special test fluid in a little compartment. You run the engine for a few minutes with the radiator cap removed. Then you draw in some air from the top of the radiator. The test fluid changes color if exhaust gas is present, typically from a bad head gasket.

Beg, borrow, or steal a handheld infrared thermometer. Measure the upper radiator hose near the thermostat. Make sure this value is close to the thermostat rating. Make sure the dash gauge is reasonably close to your measurement. For all we know, the problem could primarily be the indication reading high and the actual coolant temperature is fine, combined with a bad radiator cap venting pressure way too early. Or maybe your new thermostat is bad. Testing will help you know for sure.

If that is good, run the engine at idle. Compare the temperature at the radiator inlet and outlet. You should see at least a 30F drop. If not, that points to inadequate coolant flow. It could also be inadequate airflow through the core, but you had already tested for that earlier with a sheet of paper. Another potential problem is scale buildup inside the radiator (acts like an insulator to block heat transfer), but isn't your radiator new?

That should keep you busy for a little while. Remember, you can get free loaner tools for these tests, so don't let that stop you. For the infrared thermometer, you can get a decent one for under $30. I'd suggest just buying one as they are so handy to have.
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UPDATE:
I drove for 10 miles. Stop and up to 65 mph. The temp gauge stayed at the bottom of the operating zone. 95 out side. Got back to house and let truck idel in the driveway.( I believe the idesl is set too high) and the temp started to rise so I got out and ck the lower hose and it was collapsed. (springs will be here on Tues). I live in a very rural part of California so you cant just go buy things you need you have to get it off the internet. Any way I think the problem will be solved once I turn down the Ideal.

What do the rest of you say?

 

Great job on confirming the collapsed hose. Just be aware you may have more than one fault present. Fix the known fault and then keep a close eye on the cooling system in case the problem continues. You'd just have to continue troubleshooting, that's all.

As far as the idle speed, you might find lowering it decreases overall cooling. Set it to specs but don't go lower than that. Many vehicles have a special feature to temporarily increase the idle speed if coolant temperature gets too high. This speeds up the water pump to increase circulation. If equipped with a belt-driven fan, higher RPM increases cooling airflow through the radiator core.

 

OK, Thanks.Gary