Hello.
I have a 2000 Ford Ranger XLT with a 2.5L 4 cyl motor. I've just recently replaced the water pump. After replacing, I added new antifreeze / water mixture and proceeded to let the truck warm up full coolant with the cap off. Truck never reached running temperature, no heat would come out. I got in the truck and revved the motor to maybe 1200 rpms and the temp gauge began to climb and heat came blowing out of the vents. I figured maybe the thermostat was bad and ordered a new one from Ford. I originally didn't replace thermostat because Ford had to order it and it didn't meet my deadline to replace the pump.

Put the new thermostat in today. Drained the coolant, removed the Tstat housing, cleaned it, installed new gasket, installed new thermostat and put back together. Again, I put new antifreeze / water mixture in it, started truck with radiator cap off to allow Tstat to open, let any air out, etc. Thermostat opened, I topped off coolant and waited for it to reach running temperature. Again, it never reached temperature. If I gave it gas, the temp gauge would go up, would blow hot air. Once I let off, temp gauge went down, no hot air.

I even drove the truck down the road to see what it would do. Temp gauge NEVER even reached the regular operating temperature, not even while driving. Its never been overheated. I have 186,000 miles and this is the first real problem I've had *knock on wood*

Any ideas on what is going on? I bought a Prestone backflush kit I'm going to try to hook up and backflush in case there's a blockage somewhere and to just flush the entire system out. I'm really stuck and need my truck back as its been sitting for a week. Any help / advice greatly appreciated!