Blowing off steam can be fun, unless it’s your engine that’s blowing the steam. Many people view a cooling system as a necessary evil, building the rest of your 4x4 with cool parts and then dealing with an overheating problem. But being nervous with an engine that tends to run hot takes the fun out of a trail ride, and overheating can leave you stranded and potentially damage engine parts.
If you approach the cooling system with the same enthusiasm as you do an axle upgrade, you can be rewarded with a dependable system that you will never have to worry about. You may also be able to gain some performance and fuel economy while you’re at it!
In order to diagnose an overheating problem or build a great system, it helps to understand how the cooling system is supposed to work. Your engine produces heat as it runs. The heat is transferred to liquid coolant which is circulated through the radiator with the water pump. The radiator transfers the heat from the coolant to the air that flows through the grille. The fan blows air through the radiator to increase the rate of heat transfer.
In addition to this basic system overview, there are a couple more things you should know about. The thermostat closes off the coolant flow to the radiator to let the engine come up to temperature and to keep the engine above the minimum operating temp. The system is pressurized to increase the boiling point of the coolant. As the temperature goes up inside the system, the pressure increases. The radiator cap has a pressure release valve that’s designed to hold a specific amount of pressure, usually about 16 psi. Once the system boils, air is separated from the liquid, and it’s all over, literally.
Thar She Blows!
If your 4x4 has an overheating problem, the first step is to figure out what is causing the issue. Here are a couple of rules of thumb. If your 4x4 keeps cool on the highway but overheats in traffic or on slow moving trails, you most likely have an airflow problem. If it usually runs cool at idle, but overheats at highway speeds, your radiator probably isn’t up to par. It could be too small, not efficient enough, or clogged. This is also the case if your truck runs cool until you get into situations where you’re making a lot of power; in a mud bog or at the sand dunes, for example. If you overheat while towing, it could be either radiator or airflow, or both. Towing heavy loads is one of the biggest challenges for a cooling system.
There’s also the situation where everything has been fine for years and then the engine starts running hotter or simply overheats all of a sudden. This is usually caused by parts going bad. If the problem starts all of a sudden, it’s often a failed thermostat. If the temperature gradually increases over weeks or months, a water pump or radiator could be the culprit.
Also consider when the overheating started. If you made changes that have added significant horsepower, then more engine heat can be expected. We’ve also run into overheating problems caused by the ignition timing slipping 5 to 10 degrees, or by switching to a carburetor that was much leaner. Think about what modifications you made just before the overheating started to see if it’s a cooling system issue at all.
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