Part III concludes in this thread. Two-Pass Design
I asked Marv Beals, the public face of Jagg Oil Coolers, exactly what a two-pass design entailed and what it means in the oil cooler heat exchange world. Marv replied, “Two-pass flow configuration, as related to radiator and oil cooler flow orientation, means that there is a separator between the inlet and outlet, dividing the number of rows of the oil cooler into sections. The fluid being cooled must enter and pass through the length of the cooling tube(s), make a 180-degree turn, and make a second pass back the length of the cooling tube(s). There are a couple of reasons an oil cooler may be produced in a two-pass configuration: inlet/outlet location for plumbing requirements and/or performance. Plumbing requirements are simply where you need the inlet and outlet ports to be located in order to plumb the oil cooler. The performance reason is a bit more in depth. Low gallons-per-minute flow rate systems, such as with motorcycle applications, respond well to a two-pass flow orientation in an oil cooler that offers low restriction. This is because it gives the cooling medium greater opportunity for heat exchange by slowing the oil down just a bit. However, two-pass flow orientation is best employed when considered in the overall flow system. Contrarily, a cooler optimized for performance within a system with a single-pass flow configuration can gain a good deal of heat exchange by further slowing the oil’s flow and creating a two-pass flow configuration. But it will do so at the expense of significant pressure loss. Therefore, a two-pass flow orientation is best considered and employed systematically.”
So here we go again with a theme that just keeps cropping up every time I try to separate the different functions of an oil cooler. If we want to understand how a cooler works, we have to look at everything as a system and how each role impacts other roles. The name of the game is maximum cooling balanced with as little restriction as possible. Turbulation (mixing of the oil) offers maximum cooling, but causes some restriction.
Jagg is able to balance the two better than other coolers, offering less restriction than competitors’ coolers. The two-pass system offers much to the system’s approach to provide the optimal oil cooler for a Harley-Davidson. It may seem like I’m slagging the H-D oil cooler. I’m not; it’s a good one. It’s my second choice for a single cooler. However, I would not combine two of them in sequence because of the combined pressure drop values leading, in my opinion, to too much flow restriction.
Mounting Two 10-Row Coolers
The Jagg 10-row vertical oil cooler design mounts on the left side of a Harley, on the front frame downtube. Mounting a second one on the right side presents some logistical problems. The bracket welded to the cooler is angled to keep the cooler in line with the bike to save room rather than having the cooler stick straight out sideways. The six-row vertical coolers do stick straight out, but there are no interference problems because they are less obtrusive than the 10-row coolers. We could mount the cooler upside down, which would not affect cooling capabilities, but the hose ends wind up on top instead of the bottom. Therefore, a plumbing confusion results unless the owner likes hoses traveling in many directions. In the wacky world of H-D, sometimes mass complexity can be beautiful. We tried to mount them one on top of the other on the left front downtube, but did not have quite enough room. This would have looked cool, giving an all-business, tough appearance. Bending the bracket carefully after heating it would do the trick for right-frame tube mounting.
I asked Marv Beals at Jagg if there were a front and back to its oil coolers. I was sure that was not an issue, but it never hurts to ask. He told me I was, indeed, correct: “There’s no front and back. The problem is with the direction of the bend of the airfoil in relation to the mounting angle of the cooler on the downtube. Since these [10-row oil coolers] are designed to mount in-line behind the airfoil on the left downtube if you attempt to mount the airfoil upside down on the right side, the angle will be off.” The bracket could also be carefully cut off and rewelded at the correct angle to mount the otherwise left-handed cooler for a right-side mounting application.
Negative Vacuum Principle
The 10-row cooler is considered by some as too wide to be mounted straight out from the frame member directly into the wind. It does not bother me because I have a front crash guard on my Street Glide. However, it would not offend me if it were mounted on a Dyna without a crash guard, but ugliness and beauty are in the eye of the beholder. Jagg decided to conserve space because of the width of the 10-row cooler, so it put an angled airfoil at about 45 degrees from the face of the cooler. Now the cooler can be run back in line with the frame downtube. The cooling fins are not facing the air stream, but the cooler is running parallel with the airflow and the fins are perpendicular with the air. However, the mounting has no obstructions in front of it, allowing the air stream to flow right by without hindrance. I mention this because other oil cooler mounting locations, such as those in a horizontal lower frame mount position with a fender and wheel in front, partially hinder direct contact with the air stream. My physics education tells me that my current location will work very well, perhaps not quite as well as it would directly in the wind, but I was a little uncomfortable with it, nevertheless. The airfoil creates a vacuum between it and the outside (left) side of the cooler. The negative vacuum sucks air through from the inside or right side of the cooler. The reassuring part is that I can stick my hand down between the airfoil and cooler whenever the urge strikes to check if it’s working. All summer long, I did this at different speeds and temperatures. It works great. The hot dissipating air coming off the cooling fins was testament to this fact.
Mounting the Second Cooler
There is a second minor situation for right-side mounting and that involves the exhaust pipe partially being in the way. To resolve this, we simply angled the Jagg Ultralite frame mounting clamps by swiveling them forward a little to angle the cooler out past the front pipe. Of course, we removed the airfoil because it would no longer be at the right angle for negative vacuum to be effective. However, the rows and fins are in the wind. These frame mounts help space the cooler away from the frame on both sides to allow air to flow to both the oil coolers and the engine’s cylinders. What would be the point of obstructing airflow to the engine when we are trying to cool engine temperature down? I guess some people will think two big black oil coolers on one bike will not look right. I can tell you that I have to point out to most riders that there are two coolers on my bike as they don’t notice. If Bob Wood’s idea catches fire with the performance set and/or as a way to deal with detonation on stock bikes, then I am sure Jagg will manufacture left and right 10-row coolers.
Conclusion
I would like to make three points in closing. The first is that the 10-row Jagg cooler has less potential restriction than an eight-row Harley-Davidson cooler because more rows offer less restriction since there is more area for the oil to expand into. However, the pressure drop on the Jagg cooler is still three and a half times less than that of Harley-Davidson’s, which is a huge differential. The second point is that if using a high-performance oil pump like Feuling or Delkron, pressure drop becomes an even greater concern. Therefore, in my opinion, the Jagg coolers, which have substantially less pressure drop than the H-D coolers, now become the oil cooler of choice. Adequate oil cooling slows down the destructive oxidation forces that cause oil deterioration. Detonation, the great engine destroyer, can be tamed by adequate oil cooling, all other factors being in tune.
Finally, I think that every rider of an air-cooled Harley Davidson should consider running an oil cooler on his bike. Yes, Harleys have been running well for a long time without the benefit of oil coolers, but they have never run hotter because of EPA-dictated stoichiometric air-fuel ratios. I am going to climb out on a limb here, a sturdy one I might add, and state that I feel we are the last generation to ride air-cooled, 45-degree Harley-Davidson V-twins. Oil coolers are one factor of many that will prolong the lives of our beloved, air-cooled dinosaurs.
Donny Petersen
Tattoo Tony’s Heavy Duty Cycles
Toronto, Canada
www.HeavyDutyCycles.com 
Techline-Dec.08-Oil Coolers-Part III: Installation tips and types of coolers (cont.) 
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