I installed a new radiator and thermostat. OEM thermostat btw. It runs at the right temp when the radiator cap is off but it gets too hot when I put the cap on. I tried getting the air out by filling the radiator and reservoir then running it with the cap off. What am I doing wrong?

 

You need to have the cooling system open at the highest point

Some jack up the front end to get the radiator fill to the high point.

I just put a Tee in the heater hose no more air pockets.

Leave the cap off till coolant comes out good to go

Did you go with a new radiator cap??

Some after market ones have been 100% junk.

 

The cap is good.
I was researching other posts. I noticed like some that the lower hose is barely even warm. Maybe my thermostat isn't opening? Oh also now my heater isn't working

 

Put a nice long funnel in it. 18" one. Let it run to normal op temp. Coolant should raise and fall when it's air free. Be sure to run the heat. Your heater core could be leaking. Check for wet floors on passenger side. When's the water pump been replaced. Coolant boils well it isn't moving. But it could be you got a bad thermostat happens. So start there. Again. GL and God bless.

 

Got it!
I was being too impatient. I was only waiting til the coolant started to steam. At normal temp it started steaming. No bubbles though.
I let it run like 15 minutes with the cap off. I said screw it. It's just steam and the temp wasn't getting scary hot. After about 15 minutes I saw like 6 big blurps come up. After the last one the coolant dropped down and I was able to put nearly another gallon in.
Now the heater is hot and the AC cold. I let it idle for 30 minutes with the cap on and the temp stood where it's supposed to.
I'm going to try for 300k on the same engine and transmission on this truck. It has 243k. Next is the 02 sensors and plugs, wires etc.....