Putting the fan blades on backwards does not reverse the airflow.
It makes the curve of the blade backwards, which pretty much makes the fan useless. The airflow will still be in the correct direction, but probably about 25% of what it was.
Think about it, the blades are cupped & angled for a reason. With the blades on backwards, the fan will be pushing the air forward (from the engine compartment to the grill) rather than pulling the air through the radiator (from the outside). With the fan clutch engaged & the engine hot, your sucking the hot air from around the engine & trying to pushing it through an already hot radiator. You need to have the much cooler air from outside the engine compartment.
Check & make sure you fan is on so it's pulling the air from the outside.
