I started to use my heat about two weeks ago 85 6.9 Truck heats up very fast I would say about 5 city blocks i can feel some warmth. If idling it warms up good in 10 min . Gauge is at the A in Normal lower hose cool to touch top hose Hard and Hot. So i replace Thermostat (FORD motorcraft) , Radiator champion Aluminum has 13 lb cap , flushed and back flushed heater core , Freed the bleed ball, Fan spins freely, .Now i am still getting fast heat in cab, and gauge reading high after 10 to 15 mins min of driving . From cold start she pushes water out slowly (cap off) If i press gas it sucks it down let off of gas it comes up. gauge reading warm , heat blowing warm Fluid in radiator is cold no air bubbles coming out and no circulation going on in radiator. If i put the Cap on The top hose sucks in when i give it gas. I tested both thermostats and they opened in boiling water.

1. I Drove it to work today 15 miles one way 30 degrees outside . At 3 mile heat out of the vents were warm at 6 miles hot . I drove on the freeway 7 miles and the gauge was in the middle . When I got off driving though the city it was on the A in Normal . When I parked I checked the hose it was hot and hard. When I turned off the engine 6 am the top hose sucked flat and has stayed that way as of 12 pm lunch time. The radiator is newly installed 3 day's ago I didn't remove block plugs my extention broke trying . Do you think . Something is blocked near block plugs?

 

Is the cap working right? It is supposed to allow fluid to be sucked back from the overflow as the engine cools... and I'm not sure it's doing that.

 

Yes cap is new

 

It's new, but is it working /correctly/?

 

that looks to me like the thermostat is not opening creating a vacuum in the radiator, collapsing the upper hose.

 

i would try your old cap Darrell to see if you get the same results.