Let's talk about fixed-blade fans

[TylerW]

Hey guys:

My '71 Valiant is finished and I have been enjoying it.

But, I think I am doing something wrong with the fan/fan shroud situation.

I am using a new 22" radiator and fixed fan(no clutch).

I started out with no shroud at all, because I don't have one of those "rare" 22" shrouds nor the money to afford one. It was getting too warm at slower speeds and idle, probably 225 degrees.

I dug through my parts and came up with a shroud which I *think* I removed from a 77-78 Volare slant six. I turned it upside down and trimmed it slightly to fit.

While I was at this, I compared the fan that came from the '75 Duster 318/AC that I parted out. The Duster fan is also fixed and 5-blade but I noticed right away the pitch of the blades on the Duster fan was greater and the blades themselves larger than the fan I've been running on the Valiant.

Being out of a 26" rad car, the Duster fan is too large to fit inside that shroud, so I had to reuse the small fan. It runs cooler at slow speeds, slightly, but still creeps up at idle, and worst of all, it's heat soaking like crazy. Sometimes it's approaching 240 degrees when I restart the engine.

So obviously that fan isn't up to the job..I guess it must be a SL6 fan. What are my options within the 22" radiator set up? Pony up for one of those "correct" shrouds? Will a larger fan even go in it?

I guess I'd consider that, other than the fact that everyone I've ever dealt with here sees money signs when they know they have an uncommon part, and I'm not making that up.

 

[RustyRatRod]

What thickness core? You never said. I always have run the Mopar viscous fan on everything I have ever built Mopar and it has worked every single time. The 5 blade design is staggared and assemetrical resulting in more air being moved since each blade moves air at a different rate. That's how it is designed. It also requires the proper shroud. The correct positioning for the fan is half the blades should be inside the shroud and half out. The MP fan is a variable, thermostatic design that increases fan resistance as the temperature rises resulting in a fan that steadily increases in speed with temperature. Those things can really move some air. They are light years ahead of any fix blade fan ever made and work better than most electric fans. Also, you need to make sure as much air as possible is flowing through the radiator. Is the hood to radiator support seal in place? Are you running a valance panel? You can even add a bottom cover extending from the rear of the valance to the K frame blocking up those holes thereby forcing more air through the radiator, instead of up through the K frame. While you're at it, seal off ALL the holes in the radiator support except that which air flows through to get to the radiator. This forces even more air through that one big hole in the center. I use black foam pipe insulation. Works good and you cannot see it when done. Once you've gotten all that done, you should be well on the way to running much cooler.

 

[TylerW]

Thanks for the advice SS.

It's a 2-row radiator. Seems like it should be plenty, as this car does not have air conditioning.

I think I actually have an original Mopar clutch fan. I planned to use it on the '73 Sport, but it's not even close to being back together yet.

I was looking through the '75 FSM and thought I would post how Ma Mopar equipped various A-bodies in the day:

225-

19 or 22" radiator. No shroud unless AC and or maximum cooling pkg.
All fans fixed. Fan size 17-1/2 4 blade, AC and max cooling used 18" 7-blade

318-

19 or 26" radiator. All models used shroud.
All fans fixed except California AC and Max cooling which used fluid fan.
Manual/Auto non AC used 18-1/2" 4-blade fixed, CA used 18-1/2 5 blade flex.

AC/max cooling models used 20" 5-blade flex(this is what I have and wouldn't fit) California cars used the 20" fluid fan.

360-

All used shroud. All used 20" 7-blade fluid fan.

195 degree thermostat all models.

What I am talking about in the original post are flex fans, not fixed, my mistake.

 

[66fs]

I am a fan of OEM flex fans. Solved my problem, on a 74 Dodge Truck, same as yours. I don't trust the aftermarket ones.

 

[RustyRatRod]

Well what I referred to was a CLUTCH fan. a flex fan IS a fixed fan. It simply flexes the blades to reduce drag at high RPM. It is still a fixed blade fan though.

 

[OUTLAW]

I have used the same aluminum 7 blade flex fan since 1974 with out a shroud or a problem. I use a 2 inch spacer so the fan sits about 1 1/2" to 2" from the radiator and a 160* thermostat and can run in the worst traffic and heat and my motor NEVER exceeds 190*-195* and usually sits right on 180*

 

[TylerW]

Well just lucky enough, I found a 2863215 7-blade thermal fan in my parts collection. It fits in the shroud nicely and clears the rad, so I'll use that. Thanks again for the help.