Thread: Cooling Suggestions For Your Rod

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Cooling Suggestions For Your Rod
by Steve Jack


More conventional wisdom and no nonsense science on cooling for your cars engine. It doesn't matter what you drive or where you live, these little tidbits of information just may save you from an overheating experience. Keep in mind, as in all articles of this nature, it is difficult to diagnose all conditions that may play out, so once again, this is not meant to be a perfect, end-all to all the situations that may arise affecting your cooling system, but will definitely help you design and operate a safer and more reliable cooling system. Enjoy!

The more horsepower an engine makes the more cooling capacity it will need. More horsepower requires more fuel and more fuel makes more heat. You lose about 33% of your engine's energy in heat carried away by the cooling system. In fact, horsepower calculations can be made about an engine by simply knowing the inlet and outlet temperatures and flow in an engine.

Even at idle, fuel circuits are utilizing small amounts of fuel at low RPMs and fuel requirement changes on higher horsepower engines will dictate small incremental changes (more) at idle resulting in the production of more waste heat. This is especially true with cams that require higher idle speeds. This increase in wasted heat must be additionally dissipated by your cooling system. So plan accordingly, more radiator, more flow or hopefully both.

Designing a cooling system with the radiator cap in the upper hose is a big no-no! Certain thermostat housings that go into the upper hoses are essentially reducing a 20 something PSI cap to only a few pounds of protection at best. The pressure in the upper hose will commonly exceed the caps pressure limits and expel coolant.

Systems with low pressure caps or caps that are pressure compromised, as mentioned above, will allow coolant to be expelled during high RPMs and decrease the cooling capacity and eventually compromise the whole system. Hence, the engine overheats from a shortage of coolant. It is commonly thought that engines overheat and expel the coolant when in fact it's the opposite, coolant is expelled due do poor design and the engine therefore overheats.

Never use over a 50/50 mix of water to antifreeze ratio. Adding antifreeze to water will protect against boiling and/or freezing, but reduces the water's ability to carry or transport heat to the radiator big time. See the original Cooling Tips for a better explanation of this chemistry factoid.

Coolant temperatures are not indicative of actual metal surface temperatures. The metal temperature will have to be significantly higher to produce certain readings depending on the flow rate and location of temperature sensing. Head sensing temperatures and intake sensing temperatures can differ greatly even though the inlet temperature at the radiator is no different. A 250° indication is about the tops regardless of location to shut down the engine for recuperation. Keep this in mind when things get this hot, an aluminum head might be saved as a result.

Typical coolant pressures can build to over 16 PSI at 200° F from room temperature. Internal pressures can build to over 28lbs of pressure under certain conditions and yet pressure is a radiator's friend, if it can be contained and used productively. Pressure provides increased boiling protection, hot spot formation protection and pump cavitation prevention. For example, a typical 10 PSI increase in internal pressure can bring the boiling point of water to 240° F.

Never remove the radiator cap from a hot and pressurized system!! Notwithstanding the safety issues, the release of pressure will remove any safety margin for boiling protection and the radiator will never build pressure and/or cool down until the engine is shut off and fully cooled. This will also potentially collapse and damage hoses when the engine finally cools down. Always fill radiators when cool!This will always assure that pressure will build and provide additional protection.

New or drained systems will always have trapped air in them. Simply fill them to the top and let any extra coolant expel. Check when cool and refill if necessary. Radiators with no overflow arrangements will need some air space at the top of the radiator for natural expansion or expulsion will occur.

Never use reducers in place of thermostats. Reducers do exactly what they say they do...reduce the flow of water to your radiator. Remember, the more flow the better and more efficient your cooling system will be. Conversely, the longer the water is in the radiator the less efficient your radiator will be. Heat soaked water sitting in the block for longer periods losses it's ability to carry any more heat and thus leaves heat behind to build and eventually overcome the system.

The bigger the cooling hoses the better! The use of small "AN style" hoses will restrict flow and therefore reduce cooling capacity. This goes for small radius hoses as well. Lots of crimps and bends will produce restrictive flow and restrict cooling as a result.

High performance water pumps take little relative power and older style stock pumps are antiquated technology by today's standards. Typically, most high performance water pumps will only take a couple horsepower at most.

The lack of pressure or flow from a weak or failing water pump will always manifest itself in the rear cylinder(s) cooling (or lack of) first. Rear plug readings or exhaust temperatures that are different (leaner) than the other cylinders, might be indicative of a poor water pump rather than a mixture condition. The engine block works like a manifold pushing water through holes much like a lawn sprinkler. When the flow/pressure is low at the pump, the farthest most point in the manifold is what suffers first (rear cylinders). This is much the same as a "garden soaker hose" analogy, in that when first turned on only provides water out the immediate and closest holes and the very far end of the hose suffers delivery problems without sufficient pressure and flow and visa versa when turned off.

When upgrading to a better radiator or choosing a new one, shear surface area is what you want for the highest cooling capacity. This translates to more tube surface area.

Double and triple pass radiators are not as efficient as single pass radiators and are not recommended for street use. They require significantly higher pressures to work correctly.

When temperatures go up when running down the road at cruising speed, this usually indicates an overly lean condition. However, a like condition may be induced by altering the frontal area of certain cars and trucks with the removing, adding or modifying of air dams or simply blocking air. Removal of air dams of production cars can produce high pressure behind the radiator at speed and reduce airflow thru the radiator itself causing overheating. This is especially true on Corvettes, Camaros, Mustangs, Firebirds and the like. Custom front ends that impede the flow of air into the radiator can do much the same thing.

Another less likely cause of rising temps at cruising speeds, if using a shroud on tight engine compartmented cars (ie. Narrow-nosed street rods), the shroud may be inhibiting airflow when at speed even though the shroud is warranted when idling and at slow speeds. This can be relieved by cutting holes in the shroud and affixing rubber flapper relief valves that let air thru from the back but will close at idle to keep the air pulled through the radiator

Excellent post nitrofc. Alot of remedies for heating problems.

Very informative nitrofc, gets me thinking about the stock old radiator I plan on using. I wonder if the amount of volume your fan puts out helps any?