Vetteman61

iTrader: (1)

Hello all,

I'm asking this question here because I believe that LS engines commonly have cooling fans wired in the way I would like to wire mine, but I have no idea how to do that. I suspect you guys would be very familiar with the correct way to wire this type of setup.

I have a '71 Pontiac station wagon. A while back I sent my POA to be reconfigured for 134, changed to a parallel flow condenser and added a Pro 6 Ten compressor. The car would run hot (455 bored .60 may be the problem) when the A/C was turned on, but never ran hot otherwise. I would like to change the mechanical fan on the engine to an electric puller fan. I'll make my own shroud. I believe the correct operation of this fan should be that it comes on only when a particular temperature has been reached. I would also like to add a pusher fan in front of the rad/condenser. I believe the operation of this fan should be that it comes on any time the A/C is turned on. This car, of course, has no computer.

Is my assessment of when and how the fans should operate correct? I am unaware of how to wire and make this setup operational and would appreciate instruction. Here is a small picture to help visualize my desired physical setup.

Thank you,
Brandon

Project GatTagO

iTrader: (7)

You don't need two fans. Get a big fan and run it as a puller. Use this to control it:

http://derale.com/products/electric-...n-probe-detail

It will turn the fan on gently and also has a A/C override function. The C6 Corvette fan is a beast and will work well for you if you can fit it. The Dorman version is under $100...

Andrew

ls1nova71

iTrader: (4)

I agree. I would only use a puller fan, either one big one or two smaller ones that fit the whole radiator. Pusher fans can actually block airflow and make your problem worse.

Spaceboy1980

I would just run a switch in the head to ground a relay to cut your fan on. I would also wire the ac to trigger the same relay. It's simple and both requirements are met.

Btw, just use a big puller, no pusher.

gofastwclass

iTrader: (2)

I'm vote 4 for no pushing fan, they are nothing more than a flow restriction and a good way to lighten your wallet. A quality fan and a basic, but properly constructed fan shroud are all you typically need.

Sometimes creating baffles to help direct and maximize airflow through the radiator are helpful but depending on the vehicle and shroud design.

garys 68

iTrader: (1)

Keep your mechanical fan, make sure your fan clutch is operating as it should.
Get an electric puller fan that will fit your radiator. Stock GM, Ford, Chrysler, etc fan are very reliable, move a lot of air, available everywhere, and are much less expensive than aftermarket. Don't bother with inexpensive ebay or generic parts store fans, they don't move enough air.
Wire it to a relay that's activated by a temp switch and/or a trinary switch. This will turn on the fan if AC pressure/temp gets high or coolant temp rises. You can find the trinary switch and wiring diagram at the Vintage Air website.

Michael Yount

iTrader: (1)

I agree with Andrew -- a PWM variable speed controller is the most efficient and elegant way to control your electric fan(s). Soft start keeps the big fan motors from shocking the electrical system. Even better than that - you can set an operating temp and the unit will vary fan speed to keep the temperature constant rather than dealing with the 25F-40F operating temp delta that occurs if you use the stock ECU settings to trigger the fans. Much less parasitic load than any mechanical set up.

I've used a Delta Current Control unit ( http://www.dccontrol.com/constant_te...ontrollers.htm ) for over 15 years on my shrouded dual 11" Spal fans AND on my 7" oil cooler fan. Works beautifully. Also has an "A/C" option allowing the fans to come on whenever the A/C clutch is triggered.

As for single vs double fans - when I bought my dual 11" set up, I did so because I didn't have enough room between rad and water pump snout to fit a single fan big enough to handle my cooling needs. The twins moved the motors to either side of the water pump tight spot. Just be sure you get enough fan(s) to do the job - as mentioned above, the ebay and speed shop "specials" usually won't get it done.

I run the stock thermostat (187F) on an LS3 which results in head temps around 195F. I have the controller set to control around 202F. So when I'm cruising down the road with enough airflow to keep the car cool, head temps run right at 195F. As I slow in traffic, gradually the fans come on and then they keep the car right at 200F-205F. So only a 5F-10F range of operating temps. Oil temps in the 210F-230F range.

I couldn't have run a mechanical fan if I'd wanted to - no room. But they're big, heavy, big parasitic losses compared to a properly engineered electric. And ironically, they move the least amount of air they're capable of when you need it most - at idle. There's a reason that virtually all OEM set ups have been electric for decades.

Here's a pretty good write up on the tech -- http://www.dccontrol.com/techwrk.htm

Taxman20

iTrader: (11)

Always use puller fans if space allows it. Pushers can actually block air flow to the radiator.

garys 68

iTrader: (1)

Just one other note. If you go with OEM style twin fans, they can easily pull more amperage that the 60 some amp alternator from the 70s. So an upgrade will be required.

Pop N Wood

iTrader: (1)

Those PWM controllers are nice but aren't needed. If you are running too hot then they are just going to put the fan at full speed, might as well use a relay at that point.

I run a simple derale controller that runs off a probe in the radiator. I had to do this since no one makes a temp switch that will fit in the metric temp sensor hole in an LS head. Has worked for 10+ years now. If you have a 455 than you can get a dirt cheap 3/8 npt temp switch with pretty much any temp setting you would like. I have my fans set up to come on 10-20 degrees higher than the thermostat set point.

I don't like putting fans on dash switches. Too easy to forget.

Like everyone said get a junk yard OEM puller fan, grab the stock relays and hook it up to a mechanical temp switch.

Mechanical fans can move a lot more air than an electric, bigger motor and all, but probably not at idle. Electrics can be completely turned off when not needed. Garys 68 is absolutely right about overloading an old 40-60 amp alternator. I upgraded to an 85 amp alternator on my carb'd vehicle, but my electric fan does not have the high speed setting hooked up. LS motors are easy to cool.

I would look into an aftermarket aluminum radiator. New ones have better coolant channel designs and cool much better than the old school multi row brass ones. A three row core with all that AC condensor in front probably has some serious air flow restriction.

Michael Yount

iTrader: (1)

In addition to the dual fan OEM-type set ups, most of the OEM single fans capable of cooling the V8's we're usually dealing with also pull big amps -- most in the 35-50A continuous range. Seems 130A minimum on the alternator is usually needed to get the job done. I'm running a 145A Escalade alt. You also have to be really careful about amperage ratings as they're often advertised for fans. The "specials" are frequently amp rated with essentially no significant pressure drop across them. And, of course, they don't actually operate that way -- put a radiator in front of it and anything that's moving 2500-4000 cfm is going to pull significant amperage to do so. So crank up the alternator.

I've been putting electric fans on cars since the mid-80's - long before it was "cool" to do so. LOTS of set ups with thermal switches and relays. Once I went PWM/variable speed, I never went back. So much smoother/quieter/easier on the electrical system and more consistency on the mechanical side. Nope, they're not strictly "needed" -- but once I experienced one, I couldn't go back.

Vetteman61

iTrader: (1)

Thanks guys for all the info. Gives me a lot to consider and look into. I'll be back, I'm sure, with more questions after that. I've had a goal of trying to get 20 MPG from this 455. I've installed HEI, fitted a 700R4 overdrive and a few other things to get there. I'm hoping the electric fan will add a couple MPG to finish off the goal.

A few things I'm curious about:

1. How do you mount a temp. sensor in your radiator? Do you have to weld in a bung?
2. If I use my existing temp sending unit that's hooked up to a temp gauge under my dash, how do I get that to trigger a relay at a certain temp?
3. Do two smaller electric fans together still pull less amps than one large electric fan?

Thanks

Michael Yount

iTrader: (1)

Properly engineered and controlled electric fans are more efficient than a mechanical - but there's no way you'll come close adding 2 mpg by moving to electric fans. It's a step in the direction of greater efficiency, but that alone isn't going to net you a 10% increase in fuel mileage. Just don't want you to get your hopes up.

1) If you want to screw a temp sender or thermal switch into one of the tanks on your rad - yes, some sort of fitting will have to be added to the rad. I had to have a rad made for mine anyway, so I just specified the threaded fittings I wanted. Search around -- there are fittings designed to be 'cut' into your radiator hose that have a screw in fitting already in them --- sort of like a tee. They also used to make 'saddles' that are designed to go in a radiator hose and accept a sender or thermal switch.

One of the benefits of the PWM variable speed approach is that most use a simple thermal sensor that you push into the fins of the radiator near the rad outlet. No special fittings needed.

2) I don't think you'll be able to use a gauge sender to trigger the fan unless you build a circuit that uses the output of the sender to activate a 12V+ or ground signal -- based on your questions, that seems to be beyond the 'scope of the course'. Most folks use a thermal 'switch' -- screws in like a sender. It's a simple switch that opens at one temp and closes at another. You'd use that to trigger the fan relay -- say a switch that opens at 210F and closes at 200F. So at 200F the switch closes and allows current to move through the switch. They come in 2 prong and 1 prong. The one prong units are grounded by screwing them into the block (ground the rad if you're screwing them in there) and simply provide a ground to the prong when the switch closes - that ground can trigger the relay. The two prong units simply connect one side of the switch to the other when the switch closes. You can run ground or 12V+ through those to trigger a relay.

3) It depends. You have to simply look at the ratings of the fans. It depends on the size of the fans and motors driving them. I would say that often, but not always, two smaller fans use slightly less amperage than a single large fan with both moving similar amounts of air. Just remember how important the shroud is to moving air across as much of the rad as possible.

I appreciate you chasing that 20+ number on mpg! My best interstate tank when my car was powered by a 5.0L Ford (330hp/350torque) was 28.7. Routinely got 25-27 mpg on the highway. I'm hoping to hit 30mpg with the LS3 conversion. We'll see.

Pop N Wood

iTrader: (1)

Here is a fairly cheap adjustable unit that works off a temp probe you wedge into the radiator fins

https://www.summitracing.com/parts/flx-31147/overview/

It is only rated at 20 amps but like I said grab the stock relays when you get a junk yard fan and use the controller above to activate the relays.

Most fans draw less than 35 amps on high speed. A carb'd motor draws significantly less current than a fuel injected computer motor.