Inside the Pentstar cooling fan

23752 Views 12 Replies 9 Participants Last post by Gmontelongo, 2 mo ago

MoTech

Discussion Starter · Jun 15, 2015

Most of you know we offer HD cooling system components. Soon we will offer a cooling system solution for tough builds like 6.4 Hemi's at high altitude, blown JK's and JK's that tow.

During this diligence I have looked at almost everything that is out there. My opinion is OE fan assemblies outperform aftermarket fans for the most part. Special needs like running in mud requires a sealed motor which is not what I'm concerned with, my concern is the ability to cool the engine and transmission.

Most of you know the early JK fan is okay, not great, but it does outperform most universal 16" fans by a wide margin. The stock fan blade is about 17" in diameter. The stock fan motor is a standard single wound DC motor that has been used for decades. Two speeds are achieved by using a voltage divider to lower low speed voltage to about 8 volts. This is a cheap solution when compared to dual wound or variable speed fans but we're use to cheap in our JK's. It is common for the low speed portion of the voltage divider to burn out leaving your JK with high speed operation only. You may notice erratic AC operation and odd high speed fan behavior if your divider goes out. We replaced 3 dividers in JK's just in the last two months. If your fan motor ingests mud, contaminated water or debris it will consume more amps resulting in the failure of the divider and melting the high speed relay contacts. If this happens replace the motor and divider(Chrysler calls it the fan harness).

I was surprised when I ordered my guy to gut a Pentstar fan motor($600&#55357;&#56862

. He came to me and said I've never seen tis before. He would if he was into RC. The Pentstar fan motor is an outrunner, the outside bell rotates rather than the inner rotor. This means more torque to turn the 18.5" blade. Like a model motor the module contains 3 main drives and while I did not count about 22 poles(may be less I took a quick look).

I believe the unit is made by Johnson Electric and it is very heavy(dense) for it's size. The unit contains an electronic speed control and interface for the TIPM. The fan is listed as PWM but when I observed the pattern on a lab scope it was not a standard PWM signal; it was more akin to a step ladder voltage signal based on % fan requested.

I find the fan to be compact(due to the outrunner design) and powerful and give Chrysler credit for fitting it. I find the control and software lacking though. The TIPM controls the fan and it seems illogical. I see Pentstars run in the high 230's before the fan comes on and AC pressure exceeding 400 psi before the fan steps up. Once the fan spins up it seems to idle at 10% which I like to keep some air moving. At 100% it moves a lot of air but I notice it rarely goes above 75%, even if the engine is hot, like it is limited. I know motors of this design can have synch issues the high rpm.

As much as I would like to use the Pentstar fan on the early JK it is cost prohibitive and control is a problem. I do not trust variable speed controllers with software in extreme conditions.

We can get similar or better performance with old fashioned DC motors and high capacity relays along with lower cost, simplicity and reliability. So for now while I admire the Pentstar fan assembly we're going the KISS route.

See less See more

Save

1 - 13 of 13 Posts

CRDTom

· #2 · Jun 15, 2015

but is it sealed?

it isn't just mud which is a major issue here but also dust which can kill the 3.8 electric fans. The red dust found when travelling some areas of australia gets into literally everything and it is gritty and often corrosive.

Save

gt1guy

· #3 · Jun 15, 2015

What will you be using then?

Kevin

Save

Flyer

· #4 · Jun 15, 2015

Is the fan on more recent JKs different and more powerful?

Save

jlagross

· #5 · Jun 15, 2015

have you had a chance to modify the fan settings with a tuner?
with my traildash i am able to tell my fan to kick on "low" "med" "high" at different temps, it allows me to keep my pentastar under 220 degrees at all times,
i believe i set low to 200, med to 210, high to 219

Save

MoTech

Discussion Starter · #6 · Jun 15, 2015

Were trying a few different configurations, a dual fan set up like the Hemi passenger cars and a dual speed Ford fan good for almost 5,000 cfm.

Save

MoTech

Discussion Starter · #7 · Jun 15, 2015

gt1guy said:
What will you be using then?

Kevin

Yes we modify the Pentstar fan settings, issue is driving the Pentstar fan on an early JK.

jlagross said:
have you had a chance to modify the fan settings with a tuner?
with my traildash i am able to tell my fan to kick on "low" "med" "high" at different temps, it allows me to keep my pentastar under 220 degrees at all times,
i believe i set low to 200, med to 210, high to 219

Save

Reactions: 1

MoTech

Discussion Starter · #8 · Jun 15, 2015

Pictures, notice how the fan blade attaches to the outer can.

See less See more

Save

White13JKUR

· #9 · Jun 15, 2015 (Edited)

FWIW, BMWs (probably among others) have been using this type of fan for a while. They are variable high speed. My 2001 E46 BMW has a similar fan. I had to replace it (I think the module burns out) to the tune of ~$400.

I got mine muddy once. Other than boogering up the internals, the mud on the fan blade throws it noticeably out of balance. They also wont spin to as high of an RPM (which is part of how they move so much air).

My white 4 door E46 seems more and more similar to the white 4 door JKU sitting next to it every time I work on them.

edit: I have an RC supercub that I've upgraded the motor on to a brushless outrigger motor.

Save

MoTech

Discussion Starter · #10 · Jun 16, 2015

White13JKUR said:
FWIW, BMWs (probably among others) have been using this type of fan for a while. They are variable high speed. My 2001 E46 BMW has a similar fan. I had to replace it (I think the module burns out) to the tune of ~$400.

I got mine muddy once. Other than boogering up the internals, the mud on the fan blade throws it noticeably out of balance. They also wont spin to as high of an RPM (which is part of how they move so much air).

My white 4 door E46 seems more and more similar to the white 4 door JKU sitting next to it every time I work on them.

edit: I have an RC supercub that I've upgraded the motor on to a brushless outrigger motor.

Your E46 does have a similar set up, but different. My 06 Mercedes also has a similar fan control, in fact the Germans and high end American vehicles have had computer controlled variable speed fans for over a decade. There was a recall on your cooling fan if I remember correctly, the NTSB investigated it.

In that era most fans were brushed DC inrunners, very different than the Pentstar JK brushless outrunner. Cadillac and Ford speed controllers were unreliable, I liked the Crown Vick dual wound fan, identical in performance to the Lincoln fan but only two speeds. There were PWM operated fan clutches, hydraulic fans(Lexus), variable speed DC, dual fans, concentric electric mechanical fans......

I find it unusual to find this fan in a Wrangler, usually the Wrangler gets low tech components; I think the fan came along with the Pentstar.

The Wrangler is growing as complex as everything else. In some ways I prefer the simple Jeep which had more in common to a flathead Ford and could be fixed with a hammer. The other day I drove a V8 TJ 20 miles back to the shop in over 100 degree weather when the fan quit. 3 gallons of water at the mini-mart(poured on radiator) and downhill coasting got me back to the shop.

See less See more

Save

TAXIGIRLDFW

· #11 · Apr 22, 2017

I signed up for this forum just so that I could THANK YOU FOR SHARING ABOUT THIS FAN I drive a 2011 Dodge Caravan 3.6 , and 6 months ago at least I replaced the OEM fan because it was cracked. I have had nothing but trouble since then. I knew that the Murray replacement fan that I got at Oreily's low speed did not work, but I was confused because the High speed still worked. I have spend a lot time and money and been really frustrated with this whole thing. After the Murray fan low speed quit working, I removed the thermistor from the OEM fan that I still had hanging in my garage and put it back on, the second stage till did not work so I started trying to find the reason why like things in the tipm and the the relays, etc. After I put the OEM fan back in it works like a dream, high speed and low speed. THANK YOU SO MUCH FOR WRITING THIS.,.......You saved my engine, which has over 313K miles and going strong.

See less See more

Save

BJones156

· #12 · Aug 1, 2017

What did the signal look like?

MoTech said:
The fan is listed as PWM but when I observed the pattern on a lab scope it was not a standard PWM signal; it was more akin to a step ladder voltage signal based on % fan requested.

I know this thread is a dinosaur, but info on these motors is pretty sparse across the interwebz. So, if you don't mind, when you have time could please elaborate on the speed control signal a little further. You are correct, it is definitely not a typical pwm signal as I have run test after test with 3 different micro-controllers capable of producing a pwn signal output. None of them will turn it on at any duty cycle. I even have a control module that supposedly works for this motor, but the signal pin merely follows the input dc voltage to the module itself, giving no waveform whatsoever, just a flat dc line on the scope...yeah, weird.

Anyhow, if you could post a pic of the waveform you saw, or if you remember the shape, period, amplitude, and duty cycle that would be great! lol

-Brad

See less See more

Save