Last weekend I dumped the coolant and put in a new thermostat and upper radiator hose. When it warms up as I drive the temp gauge goes all the way up to 3/4 hot and then I guess the thermostat opens up and it runs at right about 1/2. It sits and idles at half, drives at half, doesn't move. Normal? I can't see the radiator being clogged because it runs at half when it's warmed up and stays there. I'm not sure which thermostat I have, just took the one from NAPA and didn't think to ask what temp I have until now. Should I have the radiator professionally flushed? I'm not a mechanic, just a parts changer.

Thanks

Bob

 

It shouldn't jump up then settle down. You may still have air trapped in the system.

 

Yeah, you just had an air bubble under the thermostat that was preventing it from opening. Not uncommon, easily solved, and likely all better now. If it continues then maybe reconsider.

FYI for future reference, whenever I install a new thermostat if it doesn't already have one I drill a small hole in the metal around the valve. The smallest drill bit I haven't yet broken, just enough for some air to pass thru. This prevents air bubbles from collecting under the thermostat without allowing much coolant to bypass the thermostat.

EDIT..
Also putting the upper radiator hose on the water neck is the next to last thing I do. I fill the radiator/cooling system until water comes out the water neck, then put the hose on. This let's me be sure that the thermostat is submerged in coolant.

 

Both great points , I wish I had read these post yesterday before I put all that stuff back together on my truck.

 

Thank you all for the help, I appreciate it.

Bob