For years we’ve been saying that there are times when tech questions seem to come in clumps—this is one of those times. Recently we’ve received quite a few letters dealing with cooling issues. Several dealt with pusher fans and slow speed overheating issues, and a similar number had questions about on and off set points for electric fan switches. We selected the following letters as they best represented those questions—they have been edited for length.
One Hot Pickup
I’m having an overheating problem with my 1957 Cameo pickup. It has a big-block Chevy with an 8-71 Weiand blower, a universal-type aluminum radiator, 180-degree thermostat, and dual 11-inch pusher fans thatare thermostatically controlled. There’s approximately 1/2 inch between the back of the radiator and blower pulleys. The fans are Flex-a-lite 330 (25.5x12.375 inch with a shroud), which is against the front of the radiator. Does the shroud block airflow? The fans are rated at 2,029 cfm. Do you think more cfm will work, like the Flex-a-lite 180, 16-inch, 3,300 cfm?
At 35 mph temperature is fine, but it will rise soon as the truck stopped. I’ve considered many things and believe I have a solution. Remove the existing fans and fan shroud blockage. I calculated the actual dual 11-inch-diameter square inch minus the square inch of the motors and came up with 170 square inches. The radiator is approximately 390 square inches. That leaves 220 square inches that are blocked. If the fans could be mounted as pullers, it would probably work, but, no room. So my idea is to use an un-shrouded 16-inch pusher fan. I believe un-shrouding the radiator will allow it to work at speed, keeping it cooler so when you slow down the electric fan will have less work to keep it cool at idle. I have the adjustable thermostatic controller.
Any thoughts? Thanks.
Via the Internet
A We felt there were a number of issues here. First and foremost, when doing any engine swap, start with the radiator first, allow enough room for a fan, and then put the engine where it needs to be. In cases like this the ideal fix would be to move the radiator forward or the engine back to get the needed space, but in the real world with a car, or this case a truck that’s already finished those modifications may not be viable options. So, the only other choice is to put an electric fan, or fans, in front of the radiator. Electric fans work better as pullers than pushers, but again, the options here are limited. The cure you suggest just might work, however, the Flex-a-lite 180 is a puller fan with a shroud so it’s not suited to your application. Also, be wary of fan ratings when comparing one make to another. Various testing procedures are used so cfm ratings should only be used to compare fans from the same company.
To get a fan manufacturer’s opinion, we sent Bob’s letter to our friends at Flex-a-lite, this is what they had to say:
“This is nothing more than an air supply problem. The blockage concern may hold true with your truck, when you take into account the shrouding and the radiator that’s hidden behind the core support, even the grille may play a part in this. A 16-inch fan with a true 3,000 cfm may be hard to come by. Our 398 (Flex-a-lite’s reversible Syclone S-Blade electric fan) and the 119 (Flex-a-lite’s LoBoy auxiliary pusher electric fan) are rated at 2,500 cfm and are 16 inches in diameter.” —David Heutmaker, Flex-a-lite