Mechanical fan + pusher fan question
Most of this has already been said, but let me reinforce some of it-
A lower thermostat will do NOTHING to address the issue you're having. It will just make the car run colder on the road, which isn't what you want anyway. It will still heat up at exactly the same rate at idle, so it will only extend your idle time by the time it takes to raise the temp 20°.
A pusher fan is 100% the wrong solution. You're addressing the symptom and not the cause, and adding all the wiring and amperage to run an electric fan properly is not inconsequential. And yeah, pushers are not as efficient, block air at speed, and shouldn't be necessary with a properly set up cooling system and fan.
A fan clutch SLOWS DOWN THE FAN. If you don't have one already, adding a clutch fan will not fix the problem at all, it might even make it worse. If you already have a clutch fan, try removing it and see if it fixes the issue. It could be allowing the fan to turn too slowly at idle if it's not working properly. If removing the clutch fan fixes the problem, time for a new clutch fan. If it doesn't, well, your clutch fan is fine and the issue is something else.
To fix this, you need to increase the airflow at idle. That is the problem, since you're running plenty cool when the airflow is good (at speed on the road). The most likely culprit is the water pump/fan pulley ratio, so, figure out what your pulley ratio is. Just measure the diameter of the crank pulley and the water pump pulley, it will tell you what you need to know. Factory ratio's were .95:1 for non-AC cars, they ran the HD water pump with 8 vanes. For AC cars the ratio was 1.4:1 for big blocks, with a standard 6 vane water pump...
You could have mismatched or aftermarket pulleys that are under-driving your fan/water pump too much, or even if you have the stock .95:1 pulley ratio you might not have the 8 vane pump, or maybe just need a higher ratio for your engine performance level/radiator/cooling system set up.
Most of this has already been said, but let me reinforce some of it-
A lower thermostat will do NOTHING to address the issue you're having. It will just make the car run colder on the road, which isn't what you want anyway. It will still heat up at exactly the same rate at idle, so it will only extend your idle time by the time it takes to raise the temp 20°.
A pusher fan is 100% the wrong solution. You're addressing the symptom and not the cause, and adding all the wiring and amperage to run an electric fan properly is not inconsequential. And yeah, pushers are not as efficient, block air at speed, and shouldn't be necessary with a properly set up cooling system and fan.
A fan clutch SLOWS DOWN THE FAN. If you don't have one already, adding a clutch fan will not fix the problem at all, it might even make it worse. If you already have a clutch fan, try removing it and see if it fixes the issue. It could be allowing the fan to turn too slowly at idle if it's not working properly. If removing the clutch fan fixes the problem, time for a new clutch fan. If it doesn't, well, your clutch fan is fine and the issue is something else.
To fix this, you need to increase the airflow at idle. That is the problem, since you're running plenty cool when the airflow is good (at speed on the road). The most likely culprit is the water pump/fan pulley ratio, so, figure out what your pulley ratio is. Just measure the diameter of the crank pulley and the water pump pulley, it will tell you what you need to know. Factory ratio's were .95:1 for non-AC cars, they ran the HD water pump with 8 vanes. For AC cars the ratio was 1.4:1 for big blocks, with a standard 6 vane water pump...
You could have mismatched or aftermarket pulleys that are under-driving your fan/water pump too much, or even if you have the stock .95:1 pulley ratio you might not have the 8 vane pump, or maybe just need a higher ratio for your engine performance level/radiator/cooling system set up.
