I am working on a 305 heating problem. I dive the car to work 30 miles an when i get to work the dash gage is about 150. I have a raytech gun that i check the therstate temp an its the same. I did replace the thermastate an that did not fix the problem. I check to make shure that the one i bought was good. It opened right around one 195. i reinstalled it. Refilled the engine an left the cap off. with the car in my drive way i idled up the engine an got it warm thats the only way it will warm up. Once the engine reached 195 i could c the water flow faster an the water coming out of the vaines in the raditor. Then i turned the fan on an the temp droped an the water slowed down. so it all works fine. but when driving at 56 for 30 miles with the fan off the engine wont get above 150. the out side temp today was about 60 if that matters

 

I bet more people wish they had that problem instead overheating. Outside temp is 60° and 56mph that sounds reasonable to me. The are designed to shut off at speeds above 35mph because the rushing air is enough to cool your engine.

 

Have you checked to make sure the heater core is flowing freely? Does your A/C, heater door function properly?

 

water is flowing fast through the heater hose. i let the car sit last night till it over heated an then dover it an according to the sensor an gauge on the dash it cooled right down but when i got home the dash gauge was off according to the ray tech. so i am going to try a water temp gauge that hooks straight to the engine an mounts to the piller by the driver.

 

Are you heater hoses on in the stock location? I'm asking that because the heater feed line should come off the intake & the return should go to either the top of the water pump or the pass. side radiator tank.
Does it have a heater control valve? Make sure its switching vacuum on & off w/ the heater controls.
Can you take a picture of you engine w/ the air cleaner removed?

 

Check those things and see if anything clears up. Your symptoms scream thermostat...especially since the car never gets over 150* on the highway. But you said you checked it...and it is a "new" thermostat right?

What about driving around town, under 35mph. Does the engine ever reach 190* to kick the fans on? Say, sitting in stop and go traffic/multiple stop light stops?