There are only two things you have to do to keep your truck running cool: Move water and move air. Did you think it was more complicated than that? It really isn't. But it's the simple stuff that'll get you, which is why overheating is one of the biggest culprits keeping classic trucks off the road. Actually, the problem isn't overheating; the problem is the inefficient cooling system that's causing your radiator to do the chartreuse spew.
If it's all so simple, why do so many trucks suffer from cooling system woes? We talked to a bunch of experts from the aftermarket to find out what end users-that's us-have been doing wrong, and what they can do to make this the coolest summer ever.
Radiator: Moving The Water
One of the biggest mistakes many people make is not allowing enough room under the hood for an adequate radiator and fan. The radiator that was designed to cool a 50-year-old Flathead isn't going to be up to the job of cooling a modern V-8. Oftentimes, there's isn't a lot of room in earlier trucks to accommodate the appropriate components. At that point, selecting a radiator and fan combo is determined by what will fit, instead of what is needed.
The experts recommend choosing a radiator that will provide the most surface area. Moving air will have a much better chance with a taller, wider radiator with less front-to-back thickness. Trying to move air through a thick multi-core radiator can defeat the purpose. By the time that 90-degree ambient air gets to the center of the deep radiator, that air is going to be almost as hot as the coolant it's trying to cool. Another choice you'll face is in the radiator material: either copper or aluminum. There are technical and practical advantages to both.
Copper/brass radiators were the standard for most stock radiators on older trucks. Most current vehicles are equipped with aluminum radiators, and aluminum also makes up the majority of aftermarket radiators these days. Copper/brass is still available, however. Walker Radiators continues to specialize in copper/brass radiators, and Vern Walker reminded us that copper is a superior conductor compared to aluminum. Aluminum, however, weighs less and is more economical. Hand-fabbed aluminum tanks are generally stronger (and more expensive) than stamped tanks, which have a higher likelihood of thin and thick spots that can speed up fatigue.
Another thing to consider, as explained to us by aluminum radiator manufacturers, is that copper/brass radiators may use lead solder as bond material in the tank and the fins. Lead absorbs and holds heat, which could reduce the radiator's overall cooling capability. Copper advocates respond that the pendulum swings the other way when you consider factors such as fin height. Walker, for example, claims to be unique in the fact that their tubes are spaced every quarter inch as opposed to the half inch to 3/8 inch of some other aluminum competitors. In addition, modern serpentine designs are more efficient than older straight fin designs.
Not many people modify a brand-new radiator, except to paint it. Too much paint adds a layer of thermal barrier to the radiator, and the material reduces the effectiveness of fin louvers by reducing the opening, but the manufacturers we asked agreed that a light dusting-enough to color the radiator-is not going to significantly affect the radiator. So paint if you must, but use a light touch.
Fan: Moving The Air
The world's best radiator isn't going to be able to adequately cool the engine if it's not getting enough air moving through it. Most overheating isn't occurring at speed on the interstate (when cool ram air is providing the majority of the air going through the radiator); it's happening during low-rpm cruising, or when sitting in line at a car show or a traffic light. In these cases, the cause isn't your radiator, it's your fan. You have numerous options in this area as well, including electric versus mechanical, size, number of fans, and location.
Electric versus mechanical
The advantage of a mechanical fan is that it's backed up by the power of your higher-horsepower engine, providing the kind of power an electric fan motor can only dream about. For most applications, however, that doesn't really matter. The time you really need the fan to do its job is under low-speed, low-rpm conditions when the mechanical fan can't provide enough air and there isn't enough ram air blowing through the radiator. And electric fans are generally more compact and better looking-plus, you're saving horsepower.
Size
It doesn't make sense to run a big radiator and a small fan. Choose a fan that will provide maximum coverage of the finned core area. A pair of fans may be necessary depending on the radiator's shape. Manufacturers recommend covering 70 percent of the core.
Fan location
The question is to push or to pull. Though people mount the fan in front of the radiator because there just isn't room for it on the engine side, one thing manufacturers agree on is that pulling air through the radiator from the back is far more efficient than trying to push it through from the front. One reason is the fact that a pusher fan is already blocking ram air to the radiator-and when the air hits the core, it wants to scatter and bounce off instead of blowing through. The result is that you'll lose between 15 to 20 percent of the airflow.
Shrouds
The purpose of a fan shroud is to enlarge the area of draw from the diameter of the fan to the full core of the radiator. It also helps direct air to where you want it to go, instead of where it wants to go, and it can act as a heat shield, keeping engine heat away from the radiator. If your fan is designed to install right up against the core, a shroud is not as big of an advantage; otherwise, it is a good idea. For the shroud to work best, the fan should be positioned approximately halfway into the shroud opening in order to let the air be drawn by the fan without escaping around it.
THERMOSTAT
Modern radiators generally operate under higher pressure than units from the old days. Make sure you're using a radiator cap that is the correct pressure recommended by the manufacturer. It's not recommended to remove the thermostat or replace it with a restrictor plate. Many modern engines, especially computer-controlled fuel-injected engines, are meant to function at higher temperatures, above 200 degrees. Consider that before setting up a 165-degree thermostat.
A simple test to make sure the thermostat is working properly is to submerge the thermostat into boiling water, using a thermometer to measure the water temperature to determine when the thermostat opens. A simpler test is to feel if the upper radiator hose gets hot when the engine is started. If it does, you know the thermostat is opening.
While you're at it, check all the hoses for damage. If the hose is cut or split, is swelling at any point, or feels mushy, it's time for a replacement.
WATER PUMP & PULLEYS
Very seldom can an overheating problem be traced to the water pump, unless, of course, it's not functioning or springs a leak. Occasionally, however, folks will run under-driven pulleys to reduce the power draw from the engine. At high rpm, this doesn't affect cooling, but at lower rpm, when overheating is most likely, the under-driven pump may not be putting enough water through the system to keep your truck cool. The opposite situation is a pump that is running water too fast to allow it to cool.
Straight Water Or Antifreeze?
When a stock car racer fills his radiator, he uses straight water, and he does so for two reasons. Firstly, glycol antifreeze is illegal in racing due to its slippery nature (if he crashes, the slimy stuff gets all over the track!). Secondly, straight water cools more efficiently than the traditional mix of 50/50 water and antifreeze-glycol actually gets in the way of cooling-it's simply there to protect from freezing, corrosion, and rust. If you live in a relatively warm climate, there's little or no need to run a glycol coolant in your truck's radiator.
But wait! We know that a racer isn't running around when it's freezing, but what does he do about the corrosion associated with straight water and an aluminum radiator? Nearly all the racers use WaterWetter, a product from Red Line Oil that solves that problem and a few more things that are totally relevant to you and your truck.
When water begins to boil, hot spots or vapor bubbles form. These bubbles effectively reduce the surface area available for water to take the heat away from metal in your cooling system. WaterWetter changes the surface tension of water, thus working to eliminate these bubbles. Fewer bubbles equal more cooling, allowing WaterWetter to drop coolant temps by as much as 20 degrees.
Though many of the latest water pumps feature a sealed bearing, the older ones do not. WaterWetter helps to lubricate that seal, as well as reduce the cavitation that comes at high rpm. Combined with the benefits of inhibiting corrosion and lower temperatures, WaterWetter might be a surefire way to finish off a cooling system that's well designed and works as intended. You can find it at major chains like AutoZone, Advance, and O'Reilly, as well as in mail-order houses like Summit and Jegs.
