My car overheats on long drives when the ambient temp gets above 80F. The car does not have the thermostat or cable attached to the cooling flappers. I've rotated the flapper rod and I can hear the flappers. Without the thermostat, the flappers should be in the open position, correct? But the car still overheats. Maybe the flappers are closed? Any thoughts? Thanks

Is it running lean? Timing and valve adjustment can make a difference too.

the flappers default to the full open position.

1. Define/quantify overheats?

2. What motor?

3. Carbs or FI?

The tab the bellows wire attaches to should be up. If you've never cleaned the oil cooler, chances are it's all gunked up.

Could be a multitude of things.

Is this a recent occurrence? If so what has changed since last summer or drive?

If this is a new to you car, or you have limited driving in heat on Highway ect you will likely need to start looking at things one by one.

1. Borrow a bore scope and look under the tins, verify oil cooler is leaf and gunk free. Do the same for the barrels, fan ect.

2. Check your MPS and make sure it's correct for motor and functions.

3. Confirm timing dwell ect.

4. Borrow a exhaust analyser and see where you are on mixture

5. Buy a cheap IR Thermometer and confirm actual oil temp.

Engine compartment seal good ? plug seals all in place ?,engine tin all present and in place?,no vacuum leaks? is the engine clean or oil and dirt covered ? and then all the stuff already mentioned,one or more or all these thing can have a huge difference in running temp,don't run your engine too long if its overheating it can really bugger up an aircooled engine in a big way.
Good luck.