Dirt and debris in the radiator...
Dirt and debris in the radiator core is one of the most common problems radiators fall prey to and can greatly reduce its ability to dissipate heat. Here, Don Armstrong from U.S. Radiator uses an oscilloscope to check on the condition of a radiator core.
Falling victim to radiator boil-over or having your hot rod vapor lock while cruising through town is never a good feeling. Finding yourself in the left turn lane at a red light with the engine sputtering and the temp gauge rising has certainly put a few grey hairs on my head, with some falling out completely. While I enjoy pushing my steaming hot rod through busy intersections as Joe Public lashes obscenities at me, there really isn't a good reason why any hot rod should be overheating to begin with. A properly set up cooling system should be able to keep even the most radical engine configurations in the most cramped engine compartments at or under a realistic operating temperature. That being said though, it is a common problem we see day in and day out at street rod events across the country and even on some of our own projects. But before one can tackle a cooling system issue, we need to understand the basics of said system and what causes most vehicles to overheat.
The standard liquid cooling system is made up of passages inside the engine block and heads where coolant is circulated via a water pump and cooled by passing through a radiator, controlled by a thermostat and pressurized by the radiator cap. The circulating coolant soaks up the heat from the engine as it travels through the water passages in the block and heads and is cooled by the airstream as it travels through the radiator. Once cooled, it travels back through the engine to absorb more heat. To ensure that the coolant stays above a certain temperature and that the water pump doesn't force the coolant through the radiator too quickly, a thermostat is used between the engine and the radiator. When left out, the coolant is "pushed" through the radiator and not allowed sufficient time to cool in the air stream. Conversely, the absence of the thermostat can lead to an engine that never reaches optimum operating temperature (usually between 190 to 195 degrees). In order to prevent the coolant from boiling, the system is pressurized, raising the boiling point considerably. Too much pressure, however, can cause the hoses and other parts to burst, so a radiator cap designed to release pressure at a specified point is used. The pressure released by the cap is contained in an overflow container and plumbed on a closed system that returns the coolant back to the radiator once the pressure has subsided.
An overheating situation can occur anytime the cooling system's ability to absorb, transport, or dissipate heat is breached. This can be caused by something as simple as low coolant level or a defective radiator cap to poor airflow through the radiator. The ability of the cooling system to properly circulate coolant through the engine and radiator directly affects its ability to shed heat. When the coolant's circulation is restricted by means other than the appropriate thermostat, temperatures begin to rise and the engine starts to overheat. Additionally, if the air flow through the radiator is inefficient, such as at low speeds or due to a faulty fan, the radiator will fail to do its job.
Having a vehicle that has a tendency to overheat can be a frustrating predicament to say the least. Stuck in traffic with a climbing temp gauge can make for an extremely stressful afternoon. And when this becomes your experience every time you take out your ride, those trips are going to become less and less frequent. Armed with a bit of knowledge on how a cooling system functions however can be the difference between a hot rod that overheats and a hot rod that used to overheat.
The first step in checking...
The first step in checking out the cooling system is to top off the radiator with the correct coolant mix. Able to withstand temperatures well below freezing and in excess of 250 degrees without boiling, the common coolant found in today's automobiles (including your hot rod) is a 50-50 mix of water and ethylene glycol (commonly referred to as antifreeze). The addition of ethylene glycol also introduces rust-inhibiting properties to the coolant and acts as a lubricant as well.
A high-flow Superstat thermostat...
A high-flow Superstat thermostat can flow around 22- to 28 gallons-per-minute, which is a huge increase over a standard thermostat and can oftentimes make or break the cooling system.
Here's a radiator core that...
Here's a radiator core that came into the shop whose owner complained of an overheating condition. The blocked tubes are easily visible on the right side of the core. Further inspection revealed a total blockage of approximately one-third of the radiator core due to foreign object debris. This particular core is a four row with 3/8-inch fins on 1/2-inch centers.
Sufficient airflow through...
Sufficient airflow through the radiator at all engine speeds is essential. Whether provided by a mechanical fan driven off the engine pulleys or an electric fan, both need to be complimented by a well-built shroud that directs all the oncoming air through the radiator. If it's a mechanical unit, an 18-inch, seven-blade steel fan with a 2- to 2 3/4-inch pitch is ideal.
To measure the air flow at...
To measure the air flow at idle, Don uses an anemometer placed in front of the radiator. This device tells Don if there are any dead spots in front of the radiator where the fan is not pulling air through and also gives him a baseline to compare other fans to if he decides to swap the current one out.
The proper pulley combination...
The proper pulley combination is something that should be considered as well. Here's a classic example of a motor that is notorious for running hot, the Ford Flathead. A properly-configured pulley combination, along with new water pumps will ensure this engine stays around its intended operating temperature.
The coolant that overflows...
The coolant that overflows when the pressure in the system reaches the limit specified by the radiator cap is released into an overflow tank. Many companies sell nice, compact units such as the one pictured. Unfortunately, Armstrong says these are too small for standard V-8 cooling systems.
This 16-lb radiator cap with...
This 16-lb radiator cap with a sacrificial anode inhibits corrosion of metal within the entire cooling system. The sacrificial anode is immersed in the coolant tank and the electrolysis attacks it instead of the cooling system and engine components.
A quick peek in the tank reveals...
A quick peek in the tank reveals the tell-tale sign that it has been filled to capacity on a number of occasions when the radiator cap released its pressure. A tank with 1- to 1 1/2-quart capacity would be better equipped for this system.
A small washer was placed...
A small washer was placed to restrict the flow of the bypass hose, forcing the coolant to instead travel through the radiator once the thermostat is open. Like the upper and lower radiator hoses, the bypass hose should be in good condition with no dry rot or cracking evident. Also note that the lower radiator hose should use a spiral-wound spring to prevent collapse.
This 56-ounce recovery tank...
This 56-ounce recovery tank from Trans-Dapt Performance Products will be much more efficient for proper overflow and recovery operations.