Viscous fan hub/drive

Josh 8

Well-Known Member
So I have got the a/c running on my bronco prerunner. I have since been chased a heating issue with it in stop and go traffic. It’s been so bad that there would be no way to run the ac in the boarder line. I tried all types of fans. I finally built a new shroud and went back to the stock fan and the viscous drive. I have wanted to stay away from viscous hubs for reliability, durability and simplicity reasons. But alas the only fix for it was the stock fan and viscous drive with a good shroud. Since this mod the ac works well and the temps have been reasonable. I feel confident that the temps won’t run away in a long line like at the boarder or heavy stopped traffic.

So here is my question. Is there a good reason as to why I should not run a viscous hub on the race truck (class 8)?

With the recent acceptance of the viscous hub it makes me reconsider them all together.

So does any one have any real world advise in a racing application as to why I would not want to try this? I know I would have to go with a larger fan than the one I am running now.

Please let me know...
 

Bert is my name

Well-Known Member
I've built a lot of fast street cars with engines that aren't really all that fun to drive in traffic due to big cams and low vacuum. Most electric fans are not up to cooling a roudy engine for long periods of time. Especially during summer in San diego. Viscous fans properly sized and shrouded have almost always done the trick. If an electric fan is deemed necessary for some reason I will always go for an o.e.m. type electric fan and trim / modify as necessary. The after market fans and fan controllers give up the ghost too quickly. The Volvo fans and Taurus fans have always worked well for me. For mechanical fans I usually use a motor home viscous clutch and a 6 blade fan. Chevy p-30 stuff. It's been my experience that the cooling system stuff found in the summit catalog is junk and requires way too much messing with to get right. The o.e.m.s pay their engineers really well to figure this stuff out. Lack of maintainence is usually the cause of cooling problems especially coolant flow through the radiator. Get a temp gun and look for cold spot in the radiator. My bet is the radiator is full of crap and the mechanical fan pulls enough air at low speed to compensate for it.
 

Bert is my name

Well-Known Member
Also electric fans need a dedicated circuit capable of about 40 to 70 amps peak at motor start up. They will then settle at about 20 to 30 amps once running. This means big wire like 8 gauge and a good relay. Not the cheap parts store relays.
 

Josh 8

Well-Known Member
I have found the same with electric fans. On my old race truck I used Taurus fans set on high. But on the prerunner I wanted simple.

The radiator on the race truck is in the front. This is due to it being a beam 8 truck. No need to move it to the back.

Thanks for the idea of using motor home parts. That a good idea to use e 350 class c motor home parts.

The one issue I have heard of is that a stock fan can pull the hub off the water pump shaft at high rpm (6000+).
 

Josh 8

Well-Known Member
Thinking about the viscous hub I realized the biggest difference in the application between a motor home and racing is the rpm that the engine spins. The top rpm in the race truck is 6500. With a lot of time spent at 4500. In a motor home the top is probably 3500 with a lot of time at 2250 rpm.

I don’t know if the rpm difference is going to burn the drive out. So to better define the question does any one else have any first hand experience with this?
 

Bert is my name

Well-Known Member
Some of the engines I described were capable of 8500 rpm. The thing that scares me the most about high rpm and a viscous fan is not the hub coming apart but fan blades separating. I've seen a hood with what looked like a louver punched through it from a separated fan blade. There are some clutch type fan drives that disconnect at a higher rpm. Don't remember the application. There are varying degrees of fan hub lock up available too and disconnect available too for the clutch type.
 

Josh 8

Well-Known Member
Yeah. back in the day my uncle had a 67 chevelle with that dent in the hood. I remember there was beer involved and it was parked in the driveway with about 4 guys standing around when it happened. lol.
 

partybarge_pilot

Well-Known Member
Under drive hub.

We have thousands of Baja miles on the pre-runner Bronco with a clutch type fan. If it fails, they are easy to source down south. Race truck, carry a couple of self tappers, if it fails drive the screws through it and permanently lock it.
 

Josh 8

Well-Known Member
When you say “under drive” are you talking about the slip in the hub or changing pulley size to slow it down?
 

Moss2

Well-Known Member
We have run a stock viscous fan on the race bronco for 18 years with no failures. Do swap them out after a few years although that first one probably stayed in for 10 and it probably wasn't locking up as much anymore. We use a smaller crank pulley than stock and stay below 6K rpm. a lot of time in 4-5500 range.
We do not run an electric for reliability. Since they have to run pretty much 100% of the time its hard to beat mechanical for efficiency and reliability.
 
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Josh 8

Well-Known Member
Thank you moss2. That’s the kind is input I was looking for. Do you have a recommendation for a hub and fan combo? Are you using stock parts?
 

Moss2

Well-Known Member
Don prefers good OEM parts. Not all aftermarket replacements are same quality. My 96 bronco I just changed after 275K miles but it doesn't get worked like a racer.
 

partybarge_pilot

Well-Known Member
When you say “under drive” are you talking about the slip in the hub or changing pulley size to slow it down?
Smaller crank pulley or larger WP pulley. Take your pick. Also, a good pump like a Meziere pump will take the abuse of the fan and flow more than a stock one even with the reduced speed.
 

Josh 8

Well-Known Member
Ty, party pilot
 

Bert is my name

Well-Known Member
March performance makes a underdrive pulley kit for small block Ford with serpentine belts. I do not recommend using the alternator pulley though. The alternator doesn't spin fast enough to keep the battery charged at lower engine speeds. Especially during high demand situations.
 

Josh 8

Well-Known Member
I will check that out. Thank you.
 

Mark Newhan

Well-Known Member
All of the responses are good. An electric fan isn’t a great option since it’s hard to find anything worthy. If you need an electric fan look at EFE. The motors are robust and there are a variety of blade options. Kartek stocks all of the components.
 

Bert is my name

Well-Known Member
One more thing to add and I'll shut up. If you use an engine driven fan. The back of the fan should protrude from the shroud slightly. Just less than 1/3 the depth of the fan blade pitch. And at least 3/4" of clearance to the radiator. And about the same all the way around to account for engine movement/ frame flex. I also recommend using a Shaw or Muldoon high flow fail safe thermostat.
 
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