Shop Talk: The Cooling System (Part I)

By Paul Dilger

When we talk about an engine cooling system, there are two aspects that we need to consider in discussing the maintenance of the system: the physical components of the cooling system and the coolant that goes in the system. Both the components and the coolant are equally important to the proper functioning of the system.

Figure 1 illustrates some of the typical components of an industrial cooling system — the radiator core, radiator tanks (either on the top and bottom or the sides), radiator cap, water pump, fan and fan clutches, thermostat and its housing, hoses, hose clamps, engine block, by-pass systems, pressure and surge tanks, water inner-cooler, water filter, V-belts and coolant. We need to understand the workings of the various components that make up the cooling system in order to understand the importance of the role the coolant plays in the overall system.


Figure 1 — Typical industrial cooling systemThe radiator itself consists of coolant conducting tubes, air cooling fins, tanks at each end of the core, hose connections, a fill-fitting that has an overflow drain tube, and a radiator pressure cap coupling. Radiators have a coolant drain valve on bottom tank systems (vertical coolant flow system from top to bottom) (see Figure 1). Some radiators have a cross-flow or horizontal flow system with tanks on both sides of the tubes. Drain valves on cross-flow radiators can be located on either end.

A radiator will normally last the life of an engine if it is taken care of properly. Radiators can be easily damaged, and the radiator fins can collect plant material, oil and dirt that reduce the air flow. Routine inspection of the radiator is necessary for proper maintenance, especially after applications in dry grass or hay crops that have lots of wind-born materials and bugs. Quite often, leaks (transmission oil, hydraulic oil and antifreeze) find their way onto the radiator and collect dirt. This causes an oil-caked mud, which builds up slowly over time and is often overlooked during maintenance because of its dark color on the dark radiator fins. Eventually, air flow through the fins becomes restricted.

Shop Tip: Before spending time troubleshooting a cooling system on an overheating gas engine, first check for vacuum leaks. Any vacuum leak — whether from a cracked hose, the vacuum advance, the windshield wipers, the heater duct motor, the brake booster diaphragm, the headlights or any other vacuum-related part — will cause the engine timing to become retarded. Many times the degree of overheating will be related to the degree of vacuum leakage on a gas engine.


Figure 2Radiator tubes may run either horizontally or vertically.Radiator cores have either horizontal or vertical water flow (see Figure 2). Vertical tube radiators have the least cooling efficiency, especially if both the top and bottom hose fittings are on the same side as they are in Figure 1. It’s easy to see why this would be the less effective cooling configuration over one that has the top hose on the right side and the bottom hose on the left side. In Figure 1, the main coolant current flows straight down the right side of the radiator. In this configuration, the right side of the radiator will be hotter than the left side. The best vertical tube design is when the top and bottom hose connections are in the center.

Horizontal flow radiators with top and bottom hoses at opposite corners are also more efficient because incoming hot coolant drops down into an end tank and flows uniformly across all the tubes to the left tank, where it exits to the water pump.

Shop Tip: If you have a persistent overheating problem, consider exchanging radiators for a better radiator design. If you can’t adapt another radiator due to available space, have a radiator shop custom build one for you. It’s cheaper than engine repairs caused by overheating.

External radiator maintenance entails several steps, starting with clearing out all the debris such as insects, dirt, oil and organic matter that may accumulate. Saturating all the debris with soap and water and letting it soak in before rinsing the fins will be a big help. Be careful using pressure cleaners as spray from the wand tip will bend the fins if the tip is held too close.

Fin Service Tip: After cleaning, straighten out all the fins so air can flow smoothly through the core. An old service trick is to use a course hair comb to straighten out the fins. Just run the comb down the fins, and the fins will normally lift up and straighten out.

Apply a very thin coat of heat-resistant black paint where the old paint has eroded or chipped away. In some cases, a thin coat will protect the core components from oxidizing. Oxidized metals lose some of their heat conductivity.

Internal radiator maintenance consists of periodic flushing, using only distilled water (or de-ionized water) and maintaining a safe level of chemical additives.

Sediment collects at the bottom of both the radiator and the engine block. This sediment is from the cast-iron block oxidizing (rusting) and flaking off rust particles, scale particles flaking off the water jackets, dirt particles, and silicon-silicate drop-out. These sediment agents form a mud at the bottom of the radiator and the engine block. Both the radiator and engine block can be easily flushed each time you change the antifreeze.

Shop Tip: Simply remove both radiator hoses, and, using a garden hose, rinse out the radiator core and water jacket from top to bottom. You will be surprised by what comes out of both the block and the radiator. To flush the block, you will have to remove the thermostat so water can enter through the cylinder head. The greater the water volume and pressure, the more thorough the flushing will be.


Figure 3New radiator core shown on top view and a scaled core shown in the bottom view.New machines typically don’t come with distilled or de-ionized water in the radiator. New radiator tubes, as shown in the top photo of Figure 3, slowly change to scaled tubes (bottom photo of Figure 3) over a period of time. Scale deposits due to the salt (calcium and magnesium) in tap water cannot remain in solution under the hot operating conditions of an engine, so they precipitate out into a crystalline form. This is the same scale you find around water faucets. It’s obvious that as scale builds up, coolant flow decreases, thus raising the running temperature of the engine.

Radiators and caps should be tested during preventative maintenance service (see Figure 4). The same tool used to pressure check for water leaks in radiators will also check leaks in the pressure cap. When purchasing a new radiator cap, be sure to look up the pressure setting recommended by the manufacturer.


Figure 4 — Testing holding pressure on the radiator and radiator cap.Cooling fans can have a major balance problem that causes vibrations. Fans should track evenly, or they will add to the engine’s other vibrations. Small vibrations may seem minor, but these vibrations are also transferred to the crankshaft by way of the V-belt. If the fan’s vibration resonates with a damper’s resonate frequency, the vibration can eventually crack and break a crankshaft. A crack on a fan blade calls for an immediate replacement of the fan. Once a fan blade starts cracking, it breaks quickly. When blades break, the portion flying off can cause major damage to engine parts.

Fan clutches with flexible stainless-steel blades can save fuel but also draw horsepower, depending on the operating temperature of the air passing through the radiator and striking the clutch. They have a simple operation and require no maintenance. During operation at low speeds, the blade is at maximum pitch. At higher speeds, centrifugal force flattens the blades so they easily slice through the air without causing any drag on the engine (obviously not for stationary engines like generators).

I am aware of only two types of fan clutches: viscous and hydraulic. Viscous fan clutches can couple either progressively or


Figure 5 — Viscous fan clutchesin an “on-off” manner. Viscous fan clutches are like the ones that come on some automobiles. With the engine off, you can rotate the fan blades by hand. There are some tests to see if they are operating properly, so check with the service manual for the procedures.

Viscous fan clutches that are coupled progressively are controlled by a thermal unit which is sensitive to the temperature of air flowing from the radiator core. When the air is cold, the fan rotates at a minimum speed. As the air warms up, the thermal control admits more fluid into the coupler, increasing the speed of the fan. Changes in fan speed are related directly to changes in air temperature passing through the radiator, and not to engine speed (see Figure 5).

In a hydraulic fan clutch (see Figure 6), the hydraulic oil circulation system, together with proper friction clutch material, permits predictable continuous slip of the clutches at various levels of clamping force. This clamping force is varied by applying pressure to the clutch release mechanism. The pressure is provided by the existing vehicle hydraulic source and regulated by a thermo-sensitive control valve. The valve senses engine coolant temperature and maintains an outlet pressure inversely proportional to the engine temperature. A small oil cooler is included in the oil circulation system to permit


Figure 6 — Hydraulic fan clutchessustained slipping of the clutch friction plates for continuous operation at any fan speed.

 Paul Dilger is a retired professor of agricultural engineering at Cal-Poly State University. He worked as a mechanic in the U.S. Army before attending college. After graduating from college, he taught mechanics for 25 years. He is currently a private consultant helping companies develop quality service training programs.

EDITOR’S NOTE: For more comprehensive studies on OPE engine, electrical and hydraulic certification, visit Paul Dilger’s Web site at These study programs develop professional mechanics.

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