2002 Corolla Nightmare

2002 Toyota Corolla. Long story short, bought it at 186k miles, bad motor. bought a 2003 motor w/32k (so they claimed). Swapped em out.

I have been fighting the cooling system of this car since the swap. Heres the cooling system pattern of events. Its between 80-90degrees F outside.

Start the car up, drive it onto the highway, cruise 50-55mph, the temp gauge will rather quickly reach medium cooling temp on gauge, but the heater wont blow warm. After 2-3 miles at 50-55, i take it up to 65, the temp gauge almost imediately starts to increase at a slow rate, but fast enough i can watch it climb. It'll climb almost all the way to the red on the gauge. The second i slow back down to 55-50, it'll drop back down. While its up in the high engine temp range, the heater blows hot.

I've tried and tried making sure the air is out of the cooling system, but im not sure if thats the problem or what.

Anybody got any ideas????

just an interesting note to add, the 2003 motor i put in this car had no thermostat in the thermostat housing, i installed the one out of the 2002 motor i took out, could this be an issue.

Here are all the possiblities: Bad T-stat, bad water pump, air in system, bad radiator, bad fan. So let's start with the least expensive things first. The thing that makes me think air in the system is the erratic heater operation. That should be blowing hot at mid range temp. An air pocket would prevent coolant flow. Air would also decrease water pump efficiency at high speeds because of cavitation (air bubbles spinning around pump blades). There are three good ways to burp air out: 1) Use a vacuum pump and pull 15lbs of vac on the system. 2) Jack up the front end and leave it on jack stands while you run the engine up to temp with the radiator cap off. That will force air up to the highest point.
3) Remove a heater hose from the heater core to burp air out.

You can also check temp diff between upper and lower rad hoses. Should be a difference of at least 20° with the fans running. Next I would change T-stat. Inexpensive part and you've probably already spent more time and aggravation than a new one would cost. Let us know if that helps.