Hi, car is 72 satellite with 440, 727, temp ok when driving, but in traffic starts to creep up. When i bought the car it didnt have an engine fan, only two 10" electric. When these both come on to cool engine, they kill my battery, altenator is at idle, don't think it is providing enough current.
I was thinking of going to viscous fan.
Car has 27" wide x 20" rad, 2 electric fans on front and 3.75" clearance between rad and pulley bolt holes. I think most viscous fans and clutch need a min of 4".
Any help anyone, please

I'd suggest a good ole thermal clutch fan properly spaced in a tight fitting shroud. There's a jaguar clutch fan that is the shortest available I believe (dont know the part # or the dimentions)

You should install a relay with those fans, it may help the amp draw. Electric fans can be very inefficient if they are not positioned correctly as they actually block a lot the surface area they are trying to cool.

I would suggest a fan shroud with a nice flex-lite fan.