Need cooling system help

[kb426]

Jay, when I fill this engine, I remove the top heater hose to let it bleed the air out. Unless there is a small pocket of air right at the sender, I don't think that is the case. We all know what happens when a system is airlocked. I'm going to pull the sender today and see if air or fluid is the first to come out. Right now I'm changing an oring on a real axle bearing. I hate leaks. Thanks everybody for your replies.

[kb426]

I pulled the sender. There was a tiny bit of air. It didn't make any difference. Sometime this weekend I'm going to disassemble stuff and see if I've overlooked something.

[kb426]

I know what happened, I just don't know why. I removed a bunch of parts today. I took the thermostat to the kitchen again and played with the pan of water. Works perfectly. I have a 1/2" tee coming out of the intake with the temp sender in the top and the barb going to the heater hose mounted on the side port. I installed the sender in the side port and got a 90 degree elbow for the heater hose to connect to. The hole contraption is the height  of a 1/2 tee on the run with a close coupled 90 degree barb on top. I fill the radiator again and fire it and let it warm up. It's acting just like before. I make sure there's no airlock and go for a run. It's sitting on 150 degrees again. I've turned the heater on and off many times. It has an electric water control valve. About 5 miles down the road, I turn the heater valve on and leave it on. I turn the blower on and it kinda feels about the same temp on the outlet as always. All of a sudden, the temp gauge goes up to 180. The heater had some kind of an airlock that wasn't allowing the full temp water to hit the sender. The cooling system was full when this occurred weeks ago.  I still have to figure out why that happened in the first place and then I think I'll go to the salvage yard and by a bleeder assembly from some late model car and install it in the top of the heater elbow so if it happens again, I can fix it in a few seconds. I've run the exact plumbing setup in several Ford engines and never had a problem. I don't know why I had such variations with the infared temp gun either. I think I have * off the project god and I'm ready for him to get happy. I've had more weird stuff on this project than the past 40 year collection together. Thanks for your time, guys.

[The Paisano]

Have you checked the radiator cap with a pressure tester to see when she opens up pressure? I don't think the problem is with the 5.0 .Just for the hell of it,why don't you try running it in the shop for a while and see how it does without have going down the road and having air blowing throught the coils.If that proves to be ok,then try going down the road with a piece cardboard partially over the radiator and see how that does.
And last but not least,run an ohmeter with your hot water and see what the reading are when cold and hot.IF I remember right the reading should be 15 cold and 144 ohms hot. Your gauge should test about the same .