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by Steve Jack
Concept One Pulleys
Jackstands at Old Cars Only


Preface: In continuation with last month’s feature article on cooling, another no nonsense and science lesson read on cooling for your ride. Keep in mind again, as in all articles of this nature, it is difficult to diagnose all conditions that may at play, so once again, this is not meant to be an end-all to all the situations that may arise affecting your cooling system, but will definitely help you design and operate a higher efficiency and more reliable cooling system!

1.  The more horsepower an engine makes the more cooling capacity it will need whether moving or not! 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. It’s obvious to most that a higher hp engine at higher RPMs will need a cooling capacity to befit the additional power, but what a lot of rodders overlook is that even at idle, fuel circuits are utilizing small amounts of fuel and changes that improve horsepower will likely 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 by design. So plan accordingly for more radiator or more flow and/or hopefully both when you add your horsepower goodies!

2. Designing or implementing a cooling system with the radiator cap in the upper hose is a big no-no!  Certain thermostat housings designed to go into the upper hoses are essentially reducing a 20-PSI cap to only a few pounds of protection at best. The pressure built up under normal circumstances in the upper hose at that location will commonly exceed the caps pressure limits and expel coolant.  Systems with low pressure caps or caps that are pressure compromised, as mentioned, will allow coolant expulsion during high RPMs due to pressure and decrease the cooling capacity. It is commonly and mistakenly thought that engines overheat and expel the coolant when in fact it’s the opposite usually, coolant is expelled due do poor design and the engine therefore overheats due to lack of coolant.

3. 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 absorb heat.  Pure water as we have learned is the very best heat carrier and antifreeze significantly compromises heat absorption. In warmer climates, a 25%antifreeze to water ratio is sufficient enough for most applications for minimal protection for corrosion, boiling and freezing.

4. Coolant temperatures are not indicative of actual metal surface temperatures necessarily.  The metal temperature will have to be significantly higher to produce certain readings depending on the coolant flow rate, metal thickness and media and location of temperature sensing. Head sensing temperatures and intake sensing temperatures can differ greatly by as much as 20 degrees F. Reduced engine compartment airflow at idle or slow speeds reduces the cooling of headers/exhaust manifolds and can greatly increase head sensing readings as such due to heat buildup at the exhaust ports.  However, a 250 F degree reading in any case is pause for concern and time to pull off, diagnose the problem and recuperate.

5. Typical cooling system pressures can build to over 12-PSI at 200 degrees F from room temperature. Internal pressure can build to over 25 lbs 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 pure water to 239 degrees F. However, 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 sufficient pressure until the engine is shut off, fully cooled and resealed.  This will also potentially collapse and damage hoses when the engine finally cools down if sealed hot. Always fill radiators when cool! This will always assure that pressure will build and provide additional protection.

 6. 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.

7. 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 coolant flow the more efficient your cooling system will be. Conversely, heat soaked water sitting in the engine for longer periods losses it’s ability as a function of time and as it approaches it’s corrected vapor point to carry heat and leaves a disproportionate amount of heat behind to eventually overcome the system.  Run thermostats for adequate cooling system management.

8.  The red versus green antifreeze wars!  Usually all greenish antifreezes are ethylene glycol (EG) based. But they can be red in color also. Most red antifreezes are propylene glycol (PG) based and/or called Dexcool or “Dex” for short.  These PG/Dex coolants are used in some modern vehicles and should be used with caution in other vehicles. What ever you have, never mix the two products….they are not compatible and only use distilled water with either! Mixing will cause byproduct precipitation chaos in your radiator and make a clogging mess!  When topping off, know what based product you have and use only the product base that is already in your system.  Flushing a system and switching based products is very difficult. Getting the remnants of the old product out of the block is impossible to do, so only start anew with either antifreeze from a fresh installation. There are not significant advantages to either product and with new generation EG products, it’s as good as it gets! You can run EG in less than 50/50% water ratio profiles, but it is NOT recommended for PG products. Both products are formulated for iron or aluminum parts.

9.  Altering the frontal area of certain cars and trucks with the removing, with the adding or modifying of air dams or simply blocking air can produce increases in temperatures running down the road.  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 is fan shrouds, if employed.  The shroud may be inhibiting airflow at speed even though the shroud is required when idling or slow speeds. This can be relieved by cutting holes in the fan shroud and affixing rubber flapper relief valves that let air thru from front to back but will close at idle and slow speeds.

10. When upgrading to a better radiator or choosing a new one, choose cooling capacity, not marketing hype!  This adding of “cooling capacity” translates to choosing quality and proven construction designs, multiple rows, bigger tubes, higher fins per inch, cross flow models where applicable, and single pass models only! Double and triple pass radiators are not as efficient as single pass radiators and are not recommended for street use.


Happy and coooooool cruising!

Steve Jack
Concept One Pulleys
Jackstands at Old Cars Only

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