A few days ago, a fellow 'bolter posted seeking info about six blade fans for 235/261's. I responded with the following excerpted from two posts-- ______________________________________________
TF trucks 3/4 ton and larger with sixes had a heavy duty cooling option that included a larger radiator, a fan shroud and a 20" five blade fan with eccentric blades. I think it might have been stock on some of the larger trucks, but I am not sure.
The heavy radiators are about 1/2" thicker and 2" wider, but fit into the same mounting holes on the core support as the regular radiator. If you look at a standard radiator on a TF pickup, the mounting brackets on the sides are angled at about 45 degrees to fit the mounting holes on the core support. The ones on the heavy duty radiator are not angled to accommodate the wider core and tanks. The heavy duty radiator also has mounting clips for the fan shroud. The larger radiator was not offered on 1/2 ton trucks, but it does fit. US Radiator makes replacements either with standard size tubes or smaller tubes for even greater capacity. They are available with or without a transmission oil cooler.
The fan shrouds for the sixes are very hard to find, kinda like hen's teeth. Repops and originals can be found for the V8's, but not the sixes.
The five blade fans are hard to find, but they are out there. I have found two or three over the years when searching boneyards. All of the ones that I have found have been on big trucks. I have never found one on a pickup. ______________________________________
I have a friend who is an excellent fabricator who specializes in making aluminum fan shrouds for hot rods. He has developed tools and techniques such as rolling the edge to allow the exposed fan tips to catch and channel more air just for making fan shrouds. He makes them for high end projects on the West Coast including doing the custom ones for SoCal Speed Shop.
A couple months ago, he was in my garage looking for ideas for a '56 big window that he wants to begin. He saw my factory shroud and scratched his head because he had never seen one before. I explained the high capacity option discussed in my above post. I also mentioned that there isn't one available for sixes with a standard radiator and that I occasionally see requests for them on Stovebolt, especially when someone is adding AC.
He took that as a challenge. Using my shroud as a guide and a spare standard radiator that I had laying around, he fabbed a shroud to fit the standard radiator and either the stock four blade 20" fan or the optional five blade 20" fan on either a 235 or 261.
_______________________________________________
Here are pictures of the prototype shroud that I'm about to install. The brackets will attach using the radiator mounting bolts. Since the core support is angled forward, the radiator brackets lean the radiator back to keep it vertical. Because of that, the three brackets on each side of the shroud are all different to match the angle of the radiator brackets. Making those brackets has been the tricky part. Note the bead-rolled edge where the fan tips are exposed. That increases the efficiency of the blade/fan combination. The shroud is designed to leave 1/2 of the fan tips exposed.
I'll add pix of the installed shroud once I get it in. To install, the radiator needs to come out, then the fan shroud is placed over the fan and rests on the water pump shaft to keep it out of the way, then the radiator goes back in, then the shroud gets attached to the radiator. There is not enough room to simply slide the shroud in place without removing the radiator.
That radius is excellent, it probably also reduces fan noise. The design can be used in an install where the engine-to-fan distance is greater (but the other dims are same): a "barrel hoop" attached to the opening, uses the same radius.
Here are some pix showing the factory shroud next to the new one. Note that the factory shroud is wider to fit the wider, high capacity radiator. Also note the difference in the bead-rolled edge compared to the factory flat edge.
The factory shroud mounted to a standard radiator has been in my truck for a couple years. I cut the brackets off one of the high capacity radiators that was shot beyond repair and use them to mount the factory shroud. I included pictures to show how the brackets are angled to make up for the forward lean of the core support, and also to show the factory shroud mounting tabs.
Also included is a close-up of one of the side brackets for the new shroud to show the multiple breaks necessary to fit over the radiator bracket. The pieces are more intricate than they first appear.
Why are we going through this effort, especially since 235's and 261's are typically cool running engines? Adding AC can cause cooling problems, particularly here in the Arizona desert. And it's not just an engine cooling issue because it takes increased air flow for the condenser to work properly. There are different fixes including six blade fans and electric secondary fans, but a shroud should improve the performance of the stock four blade fan to handle both AC requirements.
Panic, the way he cuts the radius is with a homemade tool. It's an old drill motor with a two flute milling bit in the chuck attached to an adjustable arm with a bearing at the other end. He drills a center hole in the sheet aluminum, attaches the bearing with a bolt through the center hole, drills a hole on the edge of the radius for the milling bit to fit through, adjusts the arm to the correct length, then simply zips the thing around and voila...a perfect circle. He can cut up to 24" holes with his gadget.
Here are some pix of the installed shroud.
He is going to make a few adjustments to the prototype. He thinks he can make ten out of a sheet of aluminum. He's probably going to make ten and get them powder-coated satin black to see if there is a market for them. If he does, I'll post his contact info in the swap meet just in case anyone is interested.
I made a similar fan shroud for my street rod from an aluminum cookie sheet that was the exact correct size. Air flow got blocked in corners, actually decreasing cooling at highway speeds. The solution was to make holes in the corners and put very thin rubber flaps over the holes. That allowed the fan to pull air through the whole radiator when stopped or in slow traffic because the flaps are closed and also full air flow through the radiator a higher speeds when the flaps are pushed open removing the dead spots in the corners.
"VW cars use that 'thin rubber flap' idea, too, to get an idea."
Good morning Ed. The challenge was finding rubber sheet thin and flexible enough to be easily sucked against the holes when required and also easily blown open. The solution I found on ebay was 1/32" thick silicone rubber.
Too Tall, I'll post an update when (if) he has them available.
Attached are a few pix of a TF high capacity radiator.The core is about 1/2" thicker, but that's hard to see in the pictures. The pix do show how the mounting brackets have a 90 degree angle from the core support to fit the increased width of the radiator as compared to the 45 degree angle of a standard radiator. The pix also show the integral mounting tabs for the factory shroud.
