Guys,

Basic question is: Is there a method to sizing your electric radiator fans if you need additional or adequate cooling?

I have a 335hp non-Mopar that overheats when it's driven much below 40-50mph and the outside temps are near 80F. It's got two shrouded electric cooling fans on its radiator, with thermal switches that kick one on first, then the other as the coolant temp rises.

The airflow I feel coming off the non-OEM fans isn't what I think of as "aggressive" - the airflow hardly pushes my outstretched hand back. I recall my old car with electric fan had a heck of a push.

So I think the answer lies in installing more powerful fans. I think I could measure the diameter and the ampere draw on my existing fans (let's say 12" fan, 5amp draw) and compare that to catalog offerings (12" fan/ 9amp draw and check the wiring gauge) to get more flow...

What're your opinions?

Thank you,
-Art

BTW - The only thing in the cooling system we haven't tried is borescoping the block to check for casting restrictions. Everything else we can think of about the cooling system has been scrutinized: radiator was bench tested, meets OEM spec, hoses are clear and not collapsing (the prob is only at low speed), proper bleeding, coolant fluid, added water-wetter, water pump flow all check out OK.

You have 5 amp and 9 amp fans on that car?

Check again.

Amperage draw determines to work an electric motor is doing.

You want something closer to 30 amp draw to cool an old car.

CFM determine how much airflow the fans will push. You will want something in the 2500 and up range depending on your needs...probably closer to the 3000 CFM range.

I have a BeCool 2760 CFM dual 11" fan on my radiator with a 20 amp draw (measured) and it keeps my big block stroker at 185-190 degrees at stand still on a cool day. This is on the low end of the factory temp gauges.

I don't think that everyone needs to these monster 30-40+ amp fans...in many cases that can be a 'BandAid' for a deficient cooling system or other engine issue. Lots of things can cause overheating besides not enough airflow. Not to say it's a bad idea to have extra cooling...just may not be necessary.

Also say goodbye to the a factory alternator with a 30 amp+ draw.

However if the motor is running cool when moving but the minute you slow down, we have overheating then it could be an airflow issue. I would look at the CFM ratings on the fans and compare to what I said above. Fan shrouds that fit tightly over the radiator also make a huge difference to make sure all the airflow is 'funneled' through the radiator.

And yes, there is a huge difference between the quality of the $50 cheapo fans and the more expensive units. I would expect to pay $250-$300+ for a quality fan/shroud setup (minus the wiring/relays/etc.)

Good Luck!

you don't need to spend 200 bucks on a fan, but you can not use the aftermarket fans for this.
I have tried literally half a dozen of them over the years and none of them pulled enough air.

there are 3 or 4 known good oem ones you can get from junkyards or new for less than 200 bucks. and of course the monster mercedes fan if you really need it.

90's maxima's have the split 2 fan setup. it works, are fairly inexpensive at the yards.

HHR fans have been known to work well, and as I recall can be had new for under 100 bucks.

T-bird fans and something similar are known to work well I think it is the concourse or something like that ford that is supposed to have a simlar fan.

and of course again the mercedes fan.

Thanks all, that's great information I can use to get started.

Feets - Those amps I gave were just guessing to illustrate an example. I haven't yet measured the draw on my existing fans, but I will now so I know where things stand.
cjskotni - Thanks, that's excellent "sample" information. I'll check the alternator capacity and work it into the solution.

Thanks again guys!
-Art

Edit: Of course, now I see the Monster Cooling Fan thread you posted Feets, I'll go read that now...

I have an HHR fan on my duster. It works very well , but it's just a stock 318. Other members on here have used it with larger engines and have been very pleased as well. I got mine from Rockauto for $60.

the HHR is nice if you want a "slap it on, plug it in" fan. it comes with it's own shroud.

but I don't like the HHR fan. I like the Jeep Grand Cherokee fan. it's 19" diameter, pulls a metric crap ton of air, and can be had brand new for about $50 from the mopar dealership.

only problem with the fan, is that it's got a taper on both sides of the fan, so you'll have to fabricate your own mount to make it work, you can't just slap it up against the radiator.


OEM fans are the way to go. they're built to run 100k miles or more, and are mass produced enough that the cost is cheap compared to an aftermarket fan that cost twice as much, pulls half the amps, moves 1/4 of the air, and blows up in 15k miles.

Have a specific year/engine for the GC fan?

uh....the year with the recall for the E-fan?


Let me search for it...

Looks like an early 2000s 4.7L Grand Cherokee. Rock Auto had one for an 01, 4.7L GC. but they want $177 for it.

I got mine from the dealer for $50 back in about 05 or 06

Just a thought i have two 10" fans on a 3row champion rad. for the hemi in the challenger
i used two differnt sencers to have fans come on first one would not kick them on till over 210° the other was 195°that was in tested on stove in.water
i wired them so come on with the key the hemi ran for bout 10-15 min idle temp would not get over 165° so i had to undo one of them
is it possible that its not coming on soon enuff and the low speed just not enuff air movement?

Is there any reason you can't run a factory style fan system? You know, proper mechanical fan and shroud, setup with the correct spacing. You don't hear of a lot of guys overheating with this setup.

my personal preference, and rationale, is that mechanical fan, although effective...never shuts off. even if the clutch goes to "near idle" on the fan, you're still spinning it with the engine...all the time...when you don't need it.

the nice thing about electric fans, is that you CAN get one that works, and wire them to ONLY work when you need them.


the whole "ma had it right" argument that guys often spout is amusing to me. If there's "no need to change anything, the engineers had it right from the factory" then why does the same guy who makes that point have bigger brakes, ported heads, camshaft swaps, stroker cranks, stiffer T-bars, adjustable shocks....

nothing beats measuring things yourself
like an engineer would

you need to buy a small
"wind speed meter"
and use it to measure
the average speed of the air entering your radiator.

Kestrel makes extremely good ones,
acceptable is the
$31 LaCrosse or the
$20 Eddie Bauer

http://www.amazon.com/La-Crosse-Technolo...osse+wind+speed

i have measured myself
with the cheap LaCrosse meter
and also an expensive and calibrated coal mining spec Anenometer
about
3600 cubic feet per minute of airflow
on a 245 HP 360 V8
at idle 570 rpm
with an AC condensor in front of the radiator adding resistance
and the viscous clutch 5 blade fan
unlocked and slipping
so that it was turning about 480 rpm

when the viscous clutch locks
and at higher RPM
the cfm of the air moved
will roughly double with doubled RPM
but the power consumed by the fan
will go up dramatically
... when the RPM doubles to 960
the fan will use between
4 and 8 times more horsepower
( for geeks raise to power of 2.4)

as you can tell from
the wimpy power
of these
13.8 volt DC electric fans,
which you can estimate by multiplying:

volts times amps times 0.8 (efficiency)
then divide by 746
to convert watts to US standard Horsepower

they can not move air in volumes
like a mechanical fan
because their motors dont have the horsepower

somewhere i have a graph of the
power consumption versus RPM
of the viscous clutch fan of a
Chrysler 340 V8,
which also showed the
power consumption of the power steering and alternator.

i have posted that graph on Moparts in the past,
i think it is in the back of John Heywoods IC Engines book.

be aware that the electric fan manufacturers
are tricky in their advertising
.. what they call CFM
is in free air with the fan standing alone,
and is not pulling through the
resistance of the radiator fins or
the air conditioning condensor, or
in some cases additional coolers

on the other hand
the cooling system on factory vehicle setups
are way oversized
... most are set up for
towing trailers
up 6 percent grades in
Death Valley national park in
120+ F outside air temperatures
while staying below
240 degrees F coolant temperature

i have run a
200 mile long
70 mph highway cruise
fuel economy test
with no fan blades at all,
using special NPG coolant
that is only 70% the heat removal capacity
of normal 50/50 ethylene glycol-water coolant,
and observed no over heating

I read a car craft article on time where they dynoed a sb chevy with a clutch fan vs a fixed fan vs an electric. If memory serves the fixed fan lost 15hp from the electric and the clutch lost about 7 from the electric. Sounds like a lot of extra money and hassle combined with sub-par cooling in many cases, just to gain a few hp.

---

My HHR fan cost less than a new mech fan and clutch would cost. If i have gained 5-10 hp for less than $100, i feel like i got a good deal. http://www.network54.com/Forum/215655/message/1066184641/Car+Craft+Cooling+Fan+Dyno+Test http://www.carcraft.com/techarticles/ccrp_0311_drivetrain_power_loss/viewall.html

I've grabbed clutch fans from the junkyard for 15 bucks. Of course you can also grab electric fans there for the same price. Even if the price is a wash between the two, I don't see a real benefit to the electric fan. You still have to hook it up to a temperature switch or mickey mouse it with a toggle switch. Then you get to watch your temp needle swing up and down as you hear the fan cycle on and off. That in itself annoys me when I hear the fan on my fwd daily driver kick on/off at idle when the a/c or defrost is on.