Idle drops when electric fan comes on

[mrk5]

I installed Windstar dual fans in the General recently. I have both fans set up on thermostatic switches. The larger fan comes on around 180°. The smaller fan comes on around 200°.

I've noticed the idle drops when the larger fan comes on. I haven't run the truck at night yet, so I don't know how it will react with headlights on. I'm also concerned about running my rock lights when the fan comes on. I know the rock lights pull 20amps.

I have a 105amp alternator on a serpentine belt setup from a '90 Camaro. Just one Optima red top battery.

Would installing a larger 140amp alternator help? Or what about a second battery? Or will the idle always drop?

Just occurred to me there is also the concern of running the winch in addition to fan and/or rock lights.

 

[4X4HIGH]

First off are you running the fans through a relay? If not you need to rewire them so they go through a relay otherwise you will cause the wiring to overheat and cause a fire.

To size your alternator properly you need to figure out what the amp draw is on everything that you plan to have running at the same time and then make sure the alternator has a minimum of at least that many amps and i would say to add 10% to that figure.

 

[BUDDY]

Put everything you can on relays & yes, the idle will drop initially until the load stabilizes & the draw is determined by the system.

Later,
Buddy

 

[dyeager535]

Relays first up, if not already done. Run your engine temp higher so the fans don't have to work as much.

IMO if the smaller fan (assuming less draw) will do the work, first swap the wiring so it's the primary.

You could add a kicker switch like GM did for AC to boost the idle. My injected motor anticipates the load of the alternator before the fan comes on, so it increases RPM just before...when the fans were both coming on with the key (problem with the system) the engine would stall as soon as it started, since the load was too great and too fast.

100amp CS130 works my fans fine, with all accessories on, including manipulating the rear power window. How much do your rock lights draw?

 

[mrk5]

Yes, the circuits have relays and circuit breakers. I bought the complete wiring kit from Summit with the thermo switches. Each fan has a 40amp relay. The kits come with a 30amp circuit breaker, but the 30amp circuit breaker didn't last on the big fan. I put in a 40amp breaker that matches the relay and doesn't exceed the 10ga wire. It's been working fine now.

I noticed today when the fan kicks on voltage drops to 12 and then recovers to 13. When the fan is not running, voltage sits at 13.5. This is all according to my volt guage in the dash.

I haven't been able to find much info on the amp draw for the Windstar fans. The continuous draw must be less than 40amps since the 40amp relay and breaker are working fine. But it must at least spike more than 30amp on start-up since the 30amp breaker wouldn't work. That's assuming it wasn't just defective out of the box.

I won't have any trouble getting the amp draw on all my other components. Although I guess I don't know about the factory headlights. I'm guessing they must be around 10-15amps.

This has all led me to wonder what is the purpose of a second battery and when do you know that you need 2 batteries?

Would a second battery "absorb" the initial amp spike from the fan starting? What about capacitor?

 

[mrk5]

Relays first up, if not already done. Run your engine temp higher so the fans don't have to work as much.

IMO if the smaller fan (assuming less draw) will do the work, first swap the wiring so it's the primary.

You could add a kicker switch like GM did for AC to boost the idle. My injected motor anticipates the load of the alternator before the fan comes on, so it increases RPM just before...when the fans were both coming on with the key (problem with the system) the engine would stall as soon as it started, since the load was too great and too fast.

100amp CS130 works my fans fine, with all accessories on, including manipulating the rear power window. How much do your rock lights draw?

The rock lights draw a total of 20amps, 5 each.

The little fan will keep the engine temps in check, at least in the winter. I haven't had the fans for the summer yet. But when the large fan wasn't working due to the malfunctioning breaker, I noticed even the small fan will drop the idle.

I was wondering if the idle drop was due to it being a carb'd motor. I thought maybe an FI motor can adjust for it and that's why the fans don't drop the idle on newer cars.

 

[cybrfire]

Crew cab is carbed and fans do not drop the idle down. 140 amp alt w/dual batteries. On relays, one comes on at approx. 180 and the other at 200.

 

[BGKYK5]

A couple random things and one question:

Does the idle speed only drop when the fan first starts up or does it drop the whole time the fan is on?

The initial current spike to get the fan up to speed can be pretty big.

Depending on the breaker, it may not trip for a brief current spike. In other words, a short 60 amp spike may not trip a 40 amp breaker. I'm guessing the constant current from the large fan is between 30-40 amps, but peak could be higher.

40 amps X 12 volts = 480 watts or about 1 HP.Assuming nothing is wrong with the alternator you are still going to see a idle speed drop with a bigger alternator due to the increased load of 1 HP.

A second battery probably won't help with the current spike. You aren't drawing any current from your batteries 'till the system voltage drops below something like 12.5 volts. The alternator will give it all it can to keep the voltage at something like 13.5 volts.

That doesn't really help solve your problem. I think that may just be one of the drawbacks of a carb and big electrical loads. I would pull the alternator and have it tested at Autozone or someplace just in case though. You could also try raising your idle speed.

 

[Cornfield creations]

I have a carbed motor and my idle doesn't drop w/ just one fan. If I turn both on manually it will pull some but not too bad. I have my small fan on auto, on a 212* switch, but I can turn on either or fan at anytime. Tell ya the truth it very rarely eve comes on. I don't sit in traffic alot in town. Going down the road it stays cool.

 

[4-play]

If you have a long duration cam and little vacuum at idle it can be a problem. If you run a Holley and your power valve isn't set right, as soon as the idle drops, so does the vacuum allowing the power valve to open. Then it runs rich and even crappier. I had to use a solenoid to boost idle when the fans come on. You can also use the solenoid when winching. I'm sure I haven't helped, just telling my story.

 

[mrk5]

A couple random things and one question:

Does the idle speed only drop when the fan first starts up or does it drop the whole time the fan is on?

The initial current spike to get the fan up to speed can be pretty big.

Depending on the breaker, it may not trip for a brief current spike. In other words, a short 60 amp spike may not trip a 40 amp breaker. I'm guessing the constant current from the large fan is between 30-40 amps, but peak could be higher.

40 amps X 12 volts = 480 watts or about 1 HP.Assuming nothing is wrong with the alternator you are still going to see a idle speed drop with a bigger alternator due to the increased load of 1 HP.

A second battery probably won't help with the current spike. You aren't drawing any current from your batteries 'till the system voltage drops below something like 12.5 volts. The alternator will give it all it can to keep the voltage at something like 13.5 volts.

That doesn't really help solve your problem. I think that may just be one of the drawbacks of a carb and big electrical loads. I would pull the alternator and have it tested at Autozone or someplace just in case though. You could also try raising your idle speed.

That answers a lot of my questions, thanks!

Yes the idle remains lower during the entire fan operation.

I have bumped the idle up a little but I think I could stand to go a bit higher, especially since the idle will drop when I go wheel in the higher altitudes.

 

[mrk5]

I have a carbed motor and my idle doesn't drop w/ just one fan. If I turn both on manually it will pull some but not too bad. I have my small fan on auto, on a 212* switch, but I can turn on either or fan at anytime. Tell ya the truth it very rarely eve comes on. I don't sit in traffic alot in town. Going down the road it stays cool.

Yeah, mine only runs in traffic and on the trail but not moving down the highway.

 

[mrk5]

If you have a long duration cam and little vacuum at idle it can be a problem. If you run a Holley and your power valve isn't set right, as soon as the idle drops, so does the vacuum allowing the power valve to open. Then it runs rich and even crappier. I had to use a solenoid to boost idle when the fans come on. You can also use the solenoid when winching. I'm sure I haven't helped, just telling my story.

Actually that is good info to know. I have a relatively long duration cam, which is also why I can't just throw TBI on my motor.

 

[jms]

Just a note of caution:
I know you live in the cold, but throw that old fan clutch and stock fan in the back of the truck when you go out crawling...

I've had electric fans for a little while. Kept the motor perfectly cool, in traffic, in 100F heat with A/C moseying through town, and the like. It was nice, and quiet to boot. August in Moab - no chance. And after a failed temp sensor resulted in an overheating episode (luckily in my driveway...), I went back to the clutch fan.

 

[mrk5]

I kept it. I also have a method to bypass the temp switch too if needed.

 

[4-play]

Actually that is good info to know. I have a relatively long duration cam, which is also why I can't just throw TBI on my motor.

I have had better luck with MAF metered FI than speed density when it comes to a long duration cam. Speed density can be done, but the tune needs to be really close for it to run well in all conditions. Some of the newer real time tuners really help get the tune right. In my car I always had to pull the chip and reburn. PITA

Just for reference my cam specs on my carbed 355 engine is:
Hydraulic flat tappet cam from Crower.
238 and 242 at .050 I have ported heads and a Victor JR. intake. It is NOT a good combo in a 4x4 but that's what it's in now. Would be a fun mudder.

 

[mrk5]

This is my cam: CompCams 268H grind, Advertised Duration: 268/268; @.050”: 218/218; Valve lift: .454/.454; LSA: 110°

 

[lak2004]

Hijack: how did you wire yours up? Got a good diagram or something you could post up? I think I finally got mine wired right but cant test it til I get the engine completely finished

 

[Blue85]

I use an air bypass to increase the idle speed when the A/C clutch engages. You could do somthing similar for the fans. I got an air solenoid from some car in a junkyard and wired it in parallel to the A/C clutch. In your case, you would connect one side to the air cleaner (PVC line?) and the other to the manifold somewhere. The amount of idle boost can be tuned with different vacuum fittings to adjust the amount of restriction, so it's best to start with a larger valve. This trick works whether you have a carb or FI and air hoses are easy to route compared to a mechanical linkage on the throttle.

I never liked the little throttle stop solenoid because it could hold the throttle from closing all the way, but it wasn't strong enough to open it if it was already on the throttle stop. So when the A/C clutch would kick in, I had to tap the throttle to let the solenoid extend.

 

[Blue85]

Hijack: how did you wire yours up? Got a good diagram or something you could post up? I think I finally got mine wired right but cant test it til I get the engine completely finished

Can you boil a pot of water and stick the temp sensor in it?