Don’t miss out on 20% OFF all radiators! sale ends today!
You have made the decision to ditch the mechanical cooling fan and switch to an electric fan, GREAT! Now you just need to mount it to the radiator. This is where you can get into trouble quickly. Many builders choose for the “quick and easy” zip-tie straps that go through the fins of the radiator core. While they technically work, they leave much to be desired, in fact these cause more problems than they solve.
The tubes in the core are very thin. This is by design, as the tubes need to quickly transfer heat from the hot coolant to the outside air. This is how a radiator cools the engine. Now slide a serrated nylon strap between the tubes and fins. Add a bit of foam on both ends to “protect” the core from the nylon locking tab and the fan mount surface. This gives the strap a little play to move around. Next, add the vehicle vibrations and add the torque from the fan when it starts. Over time, the straps saw away at the thin tubes on the inside and the fan housing rubs on the outside. Eventually this wears a hole, and you get a leak in your expensive radiator. Suddenly that $10 pack of straps isn’t quite the savings it seemed like it was. No matter how well you try, this is the eventuality of all zip-tie radiator straps. These are also included with many aftermarket AC condensers and all auxiliary automatic transmission coolers. The same warning applies.
In a pinch, these straps can get you home in an emergency, but these are not suitable for any long-term solution. Instead, you need a proper mount for your cooling fan. First, a shroud is by far the best option for both mounting and function. The fan needs a larger space to draw air through. A single high-performance 16” fan can cool most engines, but only if the fan is drawing air through the entire core. If the fan is mounted directly against the core, it is only drawing air through the 16” diameter of the fan itself, leaving a significant amount of core with little air flow at all.
Core Solution
With a bit of space between the fan and the radiator, a fully shrouded core gets full flow through the entire area, yielding fare better cooling effects. You don’t want a shroud to sit up against the core too closely. The bare minimum is ½-inch, but 1-2 inches is the recommended spacing. You need this space to allow the core to flow air properly. Above 40mph, the fan is no longer doing anything, the air speed takes over and pushes air through the core faster than the fan can. If the shroud is too close to the core, it becomes a restriction, and the air can’t pass through. With just an inch of space, the air can flow through the core and out through the fan port, providing the necessary exchange of heat.
Push And Pull
While puller fans are the most common and efficient, heavy core stack-ups can cause flow issues. Adding modern conveniences to your classic car such as AC, automatic transmission, and an intercooler for boosted engines, you can end up with over a foot of stack-up. A large AC condenser in front of the radiator alone can greatly reduce the air flow through the radiator, not to mention the increased heat from the condenser. A shroud helps reduce the effects, but there are situations where that is not enough. A heavy stack-up not only reduces air flow but also increases the temperature of the air as it passes through each core, reducing the effectiveness of each subsequent heat exchanger.
You can combat this by adding a pusher fan in front of the stack to push more air through the cores. Using both a full-size pusher and puller fan is not recommended, as this can cause lower air flow, but in certain situations a pusher can assist a puller fan. For example, a vehicle has a 24” x 8” tall intercooler in front of a 16” x 12” AC condenser, then a 12” x 12” transmission cooler, all stacked in front of a 28” x 18” radiator core. In this case, the radiator has the best flow across the top 12”, decent flow across the center 8”, and then fairly restricted flow across the lower 8” where all four exchangers are stacked. A puller fan will draw through the entire stack up, but air always flows through the path least resistance. The AC condenser isn’t getting the best flow, reducing the AC output, the transmission cooler is stuck between the other three, so it gets the hottest air flow, reducing its ability to cool the transmission fluid (another reason for an in-tank AT cooler). The intercooler gets the cool air first, but the stack up behind it creates a lot of backpressure, reducing the air flow, and the depth of the stack allows a lot of air to simply bypass the intercooler altogether. This situation is less than ideal but it is very common in the world of high-performance vehicles.
Adding a couple of 8” pusher fans in front of the intercooler in the above scenario helps move more air through all the cores behind it, compensating for the lower pressure areas of the core that is less restricted, balancing the pressure differential between all areas. Everything works better in this case. This is also the one exception for fan shrouds. A pusher should not be shrouded, as the shroud will restrict air flow to the core when the vehicle is at speed. A shroud behind a core that is only using a pusher fan is an unnecessary restriction as well.
What Does It All Amount To?
With a shroud, mounting an electric fan is easy, simply bolt the fan to the shroud and the shroud to the radiator or core support. There are situations where a shroud is not feasible due to engine to radiator spacing, or other interference concerns. In these cases, a fan ring should be used. This is essentially a mini shroud that spaces the fan the required ½” from the core, provides four legs to secure the fan to the radiator or core support. A fan ring also serves to seal the fan to the core so that the fan does not pull air from the sides of the fan frame. All non-shrouded fans need a seal around the perimeter to be the most efficient. Fan rings are also used for pusher fans to seal the fan to the core so all the air from the fan flows through the core and not out the perimeter.
The shroud or ring itself must be mounted to something. In most cases, the shroud is secured to the perimeter lip of the core (typically a wide U-channel with a 1/4” to 1/2” lip. Rivnuts and bolts or sheet metal screws are the most common method of attachment. In some cases, the shroud mounts around the radiator to the core support, with a foam seal around the perimeter of the core to seal it.
Don’t risk damaging your radiator with inferior zip-tie straps, always mount your cooling fan properly with positive fasteners and add a seal between the fan and the core if not using a shroud. U.S. Radiator recommends using a shroud for all puller-type fans and can build custom shrouds for any of radiator. Give them a call at 800-421-5975 to discuss your cooling system needs and they will design an appropriate cooling system to ensure that your investments are well protected from overheating.