How to Diagnose an Engine Cooling Problem, and Common Causes of Engine Overheating
More power, bigger tires, larger axles…these are the types of upgrades that inspire thoughts of dominating at a racetrack, climbing the biggest obstacles off road or building the ultimate tow rig. Engine cooling system? Most people don’t pay attention to that until you have an engine cooling problem or straight-out engine overheating. To help you keep the cool in your cool car, truck or SUV, we have these tips for how to identify, prevent and cure some of the most common engine cooling issues.
But first…cooling. How does a cooling system cool? As an engine runs, it produces heat, which is then transferred to liquid coolant and circulated through the radiator by way of the water pump. The radiator then must transfer the heat from the coolant to the air. Enter: the fan. It blows air through the radiator, increasing the rate of heat transfer. If those are the main players in a cooling system, then the supporting cast includes the thermostat, water pump and radiator cap.
If your vehicle is having a problem with overheating, your first step should be to identify when the issue actually started. Was it after you increased horsepower? That will produce more engine heat, and that additional heat needed a way to get out. Are you running your transmission cooler inside the radiator? That will put more heat in the radiator. But what if you didn’t make any changes to your vehicle, or didn’t need to upgrade the cooling system as part of your buildup? Sometimes cooling problems stem simply from parts aging-out.
Let’s explore possible causes for overheating problems and potential cures.
The thermostat closes off flow of coolant to the radiator so that the engine can come up to temperature, keeping the engine above the minimum operating temperature. The cooling system is pressurized to increase the boiling point of the coolant. As the temperature goes up inside the system, the pressure increases. If an overheating problem started suddenly, or running hot is inconsistent, you might be dealing with a failing thermostat.
Radiator Cap Failure
If the radiator is boiling over, the problem can often be traced back to a faulty radiator cap. The cap is rated to release pressure at a specific temperature. Raising the pressure in the cooling system also raises the boiling point of the coolant. The cap may seem to be just a cap, but make sure it’s good working condition. Check the rubber seal on the cap for holes or cracks, and push on the inside of the cap to make sure there spring has pressure. If there is doubt, replace the cap.
Typically, if the vehicle is overheating all the time and/or at speeds above 40 mph, the radiator is damaged, deteriorating or simply too small. Radiators deteriorate over time. Additionally, engine-performance improvements can make more power which means more heat. This could be a problem when the radiator is limited on space (like in a compact truck or Jeep) or if you’ve swapped a smaller engine for something bigger or much more powerful.
You’ll need the largest width and height radiator that you can fit in the space, with a high-efficiency core for the best heat transfer.
And additional note: A four-core radiator might be capable of holding a lot of coolant, but it’s challenged at letting the air flow through the thick core to pull air/transfer heat to the atmosphere. Most performance aftermarket radiators use a two-core design with ¾-inch or 1-inch tubes. You may need to upgrade from a composite, single-core radiator to a performance two-core with either aluminum or brass-and-copper construction.
Quality of the Water Pump
Like with the radiator and radiator cap, a failing water pump too can cause gradual temperature increases. This is commonly due to worn-out bearings, which will allow the shaft to move inside the housing, resulting in a leak. Before you install some cheapie replacement, keep in mind that a lousy-quality pump can cause cavitation and with that, millions of air bubbles will enter the system. The result could be hot spots in the engine and overheating. Look for high-performance water pumps since they’re designed to increase flow, especially at lower engine rpm, and may use an impeller designed to minimize cavitation.
Having the Correct Fan
Airflow is the key measurement for determining the cooling capability of electric fans. If overheating only happens in traffic and at low speeds, it’s probably an airflow issue, as the fan is the only source of airflow through the radiator under these conditions. Highway speeds naturally force more air through the radiator, regardless of how much air the fan moves. Electric fans that pull between 2,500 and 3,300 cfm will keep most engines cool. However, for extreme engine performance and towing, you’ll want to look in the range of 4,500-6,000 cfm.
Do you have a belt-driven fan? If so, do you have a fan shroud? If not, this could cause an overheating problem. Does your electric fan overheat in traffic? Then you probably don’t have the right electric fan. There are hundreds of different electric fans with various airflow specifications and mounting configurations. An electric fan that pulls 1,500 cfm can’t possibly keep 700 horsepower cool. You need to scale the cfm rating of the fan with the power output of your vehicle. But cfm isn’t the only factor – pulling air through as much of the radiator as possible is key. That’s why electric fan systems with full shrouds work so well.