Get rid of destructive heat with an external oil cooler for your engine, transmission, power steering and rearend.
Have you ever considered how hot oil gets inside your engine, transmission, differential, or power steering? Excessive engine heat can cause unnecessary wear and tear along with premature failure. In normal operation, engine oil temperature needs to be at least 212 degrees F to get rid of destructive moisture and combustion contaminants. Moisture comes from the atmosphere and from the fuel itself. The same can be said about combustion contaminants. Both contaminate the oil if they don’t burn off with enough oil temperature. If engine oil temperature doesn’t exceed 212 degrees F, which is the boiling point of water at sea level, moisture in the oil will mix with sulfur, which is one combustion by-product, and generate acids that can ultimately damage moving parts.
By the same token, excessive engine oil temperatures do another kind of damage. Conventional engine oils can tolerate temperatures of up to 250 degrees F. After that, they begin to cook and ultimately break down at 275 degrees F. Ideally, we will hold engine oil temperatures between 230 and 260 degrees F. Synthetic engine oils, such as those from AMSOIL, are far more tolerant of temperature extremes well above 300 degrees F. They can take the punishment of the high engine temperatures encountered in motorsports.
Conventional lubricants are refined from crude oil that gets pumped out of the ground. Contaminating elements such as sulfur, nitrogen, oxygen and metal such as nickel or vanadium are always in crude oil and cannot be completely removed through refining. Oil refining processes separate the various types of molecules in the oil by weight, leaving molecules similar in weight but dissimilar in structure, which hurts performance. Although synthetic lubricants are considerably more expensive, they contain no contaminants. The dividends they yield over the life of an engine cannot be measured. We’ve torn down engines that have had a steady diet of synthetic lubricant over their 200,000-mile life only to find no visible or measurable wear on journals, bearings, cylinder walls, and piston rings. Therefore, AMSOIL synthetic lubricants are money well spent in what they yield in engine life.
How Engine Wear is Defined
Abrasive wear begins with contaminants from outside the engine, such as dirt and soot. These contaminants get into the engine via the air intake and circulate throughout the engine, grinding and doing damage to metal components. Most abrasive wear can be eliminated with high-quality air and oil filters. Never buy cheap filters.
Corrosive wear, also called chemical wear, results from chemical attack on a metal surface, such as cylinder walls and bearing/journal surfaces. Chemical corrosion is a problem for vehicles we seldom use, such as street rods and muscle cars, because they sit for long periods of time.
Adhesive wear is caused by metal-to-metal contact under high loads, speed, or temperatures where oil breaks down and doesn’t provide a barrier between moving parts. Although the metal surfaces in your engine appear smooth to the naked eye, they contain microscopic high spots, known as asperities. As asperities slide against each other, they can bond causing the two surfaces to adhere and tear each other up. As these metals pull apart surface imperfections accumulate over time leading to failures. Engines lock up due to asperities where parts fuse together.
Fatigue wear occurs when regular stress on a lubricated surface causes fractures over time. Fatigue wear occurs predominantly in rolling-element bearings according to AMSOIL.
Engine oil isn’t just about lubrication, but also heat transfer just like your engine’s coolant in the radiator. Because oil has intimate contact with your engine’s moving parts, it has the task of carrying heat away from the engine’s hottest components like bearings and valve stems. When oil temperatures reach 275 degrees F and oil begins to “coke” and stops being a lubricant. It also stops carrying heat away from the hottest parts. Sludge is a good example of what happens to engine oil when it overheats and becomes contaminated. Sludge is nothing more than cooked engine oil and contaminants.
When engines are competitive and power demands increase, oil then has the tougher task of taking on increasing temperatures and extreme shock loads. Oil temperature can be controlled by giving it a place to get rid of excessive heat. The installation of an engine oil cooler gives excessive engine heat a place to go. An engine oil cooler does the same job as the radiator. It also does the same job as cooling fins on air-cooled engines. It is a heat sink that transfers heat away from the engine to the atmosphere. An oil cooler is plumbed to the engine’s oiling system via an oil filter adaptor and braided hoses that can withstand the heat and pressure. It must also be located in the slipstream in front of the radiator or be equipped with a cooling fan if it is placed underneath the vehicle.
Another important issue with oil coolers is temperature control. You want to keep oil from getting too hot. You also want temperatures to reach at least 212-degrees F in order for moisture and contaminants to evaporate out of the oil. This sometimes calls for the use of an inline thermostat, which controls oil flow through the cooler.
Getting the Heat Out
Oil coolers, like radiators, conduct and transfer heat to the atmosphere. The humble automotive radiator is a large heat sink with tanks at each end (cross flow) or top and bottom (vertical). In between, these end tanks are a series of tubes in which coolant travels. Around the tubes are cooling fins that carry heat from the tubes full of coolant to the air passing through. The more tubes and fins you have in a cooler, the more effective the heat transfer. Your engine’s water pump moves coolant from the radiator to the engine and back to the radiator again. Coolant flow is controlled by a thermostat, which controls the flow of coolant based on engine temperature. When the coolant inside the engine reaches a given value (160, 180 or 195 degrees F), it opens releasing hot coolant to the radiator.
What makes most oil cooler applications different than an engine’s cooling system is the absence of the thermostat just mentioned. Depending upon what you subject your engine to, you might need an oil cooler thermostat to control oil temperature. Otherwise, oil flows continuously from the engine’s oiling system through the cooler and back to the engine. Like the radiator, the oil cooler is a series of tubes and cooling fins. Cooling fins take the oil’s heat and radiate it to the atmosphere. The larger the oil cooler, the more effective it is at heat transfer. And larger isn’t always more effective. Better oil coolers have more tubes and fins within a given area to conduct heat.
How To Choose An Oil Cooler
Engine oil coolers come in many types and sizes. Choosing the right oil cooler for your street rod calls for these six basic considerations.
Total oil capacity in your engine’s lubricating system
Power output of the engine and how the vehicle will be used
Amount of airflow needed and available mounting area available
What you can afford
There are two basic types of oil coolers: tube and fin, and plate or stacked plate, which works the same way but employs a different architecture with more surface area. Tube and fin coolers are typically referred to by the number of passes the fluid/oil makes through the length of the cooler before returning to the engine. A two-pass cooler is a design that allows the oil to run through the cooler length twice. The more passes a cooler offers, the better the heat-transfer qualities.
There is also inlet and outlet size. Be sure to choose a size that will not be too small and restrictive, as this will result in oil pressure drop that could cause engine damage. Most engines will use an -8 AN or -10 AN size fitting, though high-capacity/high-flow engines can also go to -12 AN port sizes on occasion. You want liberal oil flow through the cooler in order to afford good heat transfer.
The main thing you want to remember with any engine oil cooler installation is air flow across the cooling fins, whether it’s in the slipstream in front of the radiator or with help from a cooling fan. Also keep in mind you can have excessive air flow to where the boundary layer keeps air away from cooling tubes and fins. You want air to flow over the fins and tubes to where heat transfers to the atmosphere. If air travels too fast over the tubes and fins, heat is trapped and doesn’t have a chance to escape.
The best placement for oil cooler (with no electric fan) is in a location exposed to a maximum amount of airflow, which allows the cooler to operate as efficiently as possible. You must watch out for air conditioning condensers, transmission coolers, and the like, which can hinder airflow across the oil cooler. Also keep in mind an oil cooler should never be placed where road debris can inflict damage such as a wheel well. If you’re going to place a cooler underneath the vehicle, you’re going to need an electric fan to keep air moving across the fins.
The best place to tap into the engine’s oil supply is at the oil filter because the filter follows the oil pump, so the oil supply will have adequate pressure to move through the lines and cooler efficiently. Trans-Dapt has sandwich adaptors that enable you to tap into your engine’s oil supply safely and effectively. This approach also enables the oil cooler to cool oil before it is used by the engine. Minimize length and the number of bends in your oil lines where possible, which can cause fluid turbulence in the lines. The best way to add an oil cooler is via a sandwich adapter, where a spacer plate is positioned between the filter mount and the factory filter. Another option is a spin-on adapter that uses a filter relocation kit that locates the filter mount to a more convenient spot. A round two-port O-ringed metal hockey puck style mount replaces the factory filter and routes oil lines to the new filter location.
You also might want to consider a remote oil filter location for the engine primarily, which will enable you to improve filter access and even add a second filter depending upon the kind of driving you intend to do. Dusty desert conditions mandate as much filtration as you can give your hot rod. Never cut corners with hoses and plumbing. Opt for the best braided stainless-steel hoses and hard lines where possible. It is also a good idea to have an oil temperature gauge inline in order to keep an eye on temperature.
Speedway Motors offers a variety of engine and transmission coolers and adaptors from AFCO, Earl’s, B&M, TCI, Mr. Gasket and Barnes Systems. Earl’s race-proven lightweight and efficient aluminum oil coolers are engineered to fit in the kind of tight space constraints we find in street rods. Speedway Motors tells us race cars have employed brazed aluminum modular oil coolers since World War II. It was state-of-the-art technology then and remains the choice of racers and enthusiasts now.
The stacked plate modular oil cooler so common today dates to the early 1930s when it was developed for use with the Rolls Royce Merlin V-12 engine that powered the Spitfires and Hurricanes that won the Battle of Britain. This type of cooler with its “turbulator” plates and dense cooling fins provides maximum liquid and air side surface area. The large collector tanks at each end ensure minimum flow restriction. What this means for you is maximum heat transfer from a compact oil cooler.
The main thing you want to understand with fluid coolers is what they’re designed for. Engine oil coolers are designed for greater pressures and temperatures than transmission or power steering fluid coolers. This means you need to know what the cooler you have in mind is designed for. You do not want to run a transmission or power steering fluid cooler as an engine oil cooler.
Here’s what you need to know about Earl’s engine oil coolers from Speedway Motors.
- They are manufactured in the United States from aviation-grade aluminum alloy using the latest vacuum brazing technology. This means durability.
- Corrugated screen internal turbulator plates in Earl’s coolers increase both thermal efficiency and mechanical strength resulting in the most efficient, smallest and lightest practical package.
- Manufactured from thin aluminum plates for the most efficient possible heat transfer.
- Inlet and outlet fittings O-ring to the top plate assembly for easy service.
- They are designed for the range of oil flow and air speeds encountered in high performance automobiles, which means they will exceed your expectations.
- Every Earl’s cooler is pressure checked to 175 psi. Periodic samples are burst tested to 350 psi to make sure they meet standards.
Speedway Motors also offers several different types of oil filter adaptors for street rod applications. These are universal oil filter adapters that come with four different thread size adapters to make installation straightforward for GM, Ford, or Chrysler applications. Most of these adaptors are designed to be installed between the engine and oil filter to route oil under pressure through an oil cooler. Here’s what you need to know about these adaptors before selecting.
- 3/8-inch NPT side ports
- Special thread adapters cover most engines
- Die cast aluminum construction
- 1-7/8-inch thick
- All O-rings included with kit
Threaded adapters included:
- (1) -inch-16
- (1) 11/16-inch-18
- (1) 13/16-inch-16
- (1) 7/8-inch-20
All are 1-inch-12 thread OD.
Coolers for Other Purposes
Transmission, differential, and power steering coolers do the same thing an engine oil cooler does. They transfer heat away from the lubricating oil. Although it may seem like transmissions, differentials, and power steering run cooler than engines, exactly the opposite is true. Automatic transmission temperatures can run as high as engine oil temperatures because there’s a lot of friction and pressure going on in there. Differential temperatures can run as high as 300 degrees F depending upon your driving. Ditto for power steering fluid, which is hydraulic and always under pressure. It is a rare occasion a street rod is going to need a differential cooler, which is typically found only in racing. Differential cooler pumps can be electric, or driveline driven.
The same rules apply with these fluid coolers. They should be placed in the slipstream in front of the radiator with proper airflow management conducive to good heat transfer to the atmosphere. If you must place the cooler underneath away from the grille, such as the differential, power steering, or automatic transmission, you’re likely going to need an electric cooling fan, which calls for the electrics necessary to power the fan. You will need a switched power source from the ignition switch with a relay to handle the electrical load. A differential cooler will need to be in back near the rearend, yet never in a wheel well where it could be damaged by road debris.
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