i've got the single stock fan and an aftermarket pusher fan on my car. when i turn both fans on at idle the rpms drop about 400 rpm and the engine will die unless i feather the gas a bit. anything above 1200 rpm and it is fine. if i just use the pusher it does fine. no drop in rpm. has anyone ever had this issue?

 

mech or electric fan?

 

electric. brand new alternator tested and working well. volt gauge does not drop more than a half a volt down to about 13 to 13.5.

 

Look at a Zirgo fan. I am replacing my dual fan set-up with a single 16 inch Zirgo that puts out over 3000CFM.

 

put a multimeter on the battery and turn the fan on and see what voltage the battery is actually at when that fan is on.

 

i'll check the voltage out tonight or tomorrow. will let u know.

 

ok. this is with the engine off. the floating was voltage was 12.61. with the aftermarket proform fan on the voltage was 12.21. with the factory fan it was 12.15. with both it was 12.00 even.

 

if your multi meter able to measure amperage? im curious to see what kind of amps the stock fan is pulling.

try disconnecting the pusher fan and just run the stock fan and see if it drops.

 

not sure about the amperage option but i will check when i get back home. will check the fan out later today hopefully. thanks!

 

sorry. haven't had a chance to swap the fans yet. its been raining pretty hard here for the last few days. think its supposed to be a nicer day tomorrow.

 

im thinking the stock fan motor is going out and drawing more amperage than it should, causing the issue at low rpm since the alt generates more power at higher rpms.

 

the motor is brand new. just replaced it a month ago. i finally got a chance to try it out. the stock fan on and the aftermarket unplugged. when stock one comes on it definately puts a load on the alternator but after 2 seconds of running it recovers easily. like it should. i went ahead and plugged both of them up. turned them on it dropped around 300 rpm but then after 3 seconds or so it recovered 200 rpm. i gues it has worked itself out some atleast. i haven't changed a thing. i think what i'm gonna do is hook one up to a thermostatic switch and the other up to a toggle.

 

sounds like you need a bigger alt to run both fans.

 

you shouldnt see any drop in rpm when the fan kicks on normally.

 

i've got an overdrive pulley that is supposed to increase the charging capacity about 30%. got it from March. i'll probably slap it on this weekend maybe and try it out to see if it makes a differance.