If you needed extra cooling, and could fit a plate cooler in a tank that had a concentric as the OE choice — that’s a possibility. Would you be doing a “stuff job,” reducing coolant circulation, if you installed the largest possible one that would fit? You’ve got a safe “balance” if you install an OE equivalent.

That doesn’t mean the OE design is the perfect choice. Vernon noted, “There’s no way to tell how much ‘overage’ (extra capacity) there is in the OE design. Did the OE cut it right to the edge... deciding this vehicle is not going to be driven on a hot day, pulling a trailer in Arizona? Or did the O.E. overdesign?”

The company making the heat exchanger never knows. The vehicle manufacturer provides specifications for heat transfer, the heat rejection of the oil, the pump flow, maximum allowable operating pressure, transmission pressure controls, shape and size of the tank, even the line sizes, Vernon explained. He recalled a case where Long took the specs, “designed to meet them and probably exceed them by about 15 percent. The specs were off. The transmission was running hot and having problems. So we got the additional sale of an auxiliary oil cooler for those applications.”

Advantages of an Auxiliary Cooler. If there’s space for a good size auxiliary cooler, that’s probably the surest way to get extra transmission or engine oil cooling for a vehicle in severe service. It’s a lot more work to find an area to install the cooler, make good tubing connections (without being forced to use line routings and small fittings that can impede flow). If you can find the space for an auxiliary cooler, you will get better performance than with an in-tank type alone (chart, FIG.4). As the chart illustrates, there’s a broad performance range depending upon design, so it is possible for a concentric in-tank to perform as well as a smaller plate type or an auxiliary cooler.

One thing to consider in cases of borderline cooling: remember that the radiator assists in the cooling of the oil, and if you’re servicing a defective radiator, this repair may be what’s necessary to improve the performance of the oil cooler. If both the engine coolant and transmission fluid are running too hot because of the climate, type of operation, etc., a higher-performance radiator could be the answer. In addition, a new fan clutch, or if equipped with an electric fan, a new thermoswitch may be in order.

Getting By With A Concentric to Replace a Plate-Type. What about another possibility — replacing a plate cooler with a concentric tube? As Vernon observed, saying the obvious, “Long doesn’t condone the use of any type of oil cooler but the OE selection.” But this is a competitive business and as Vernon admitted, “The oil cooler is the second most expensive part” in radiator repair.

A brass concentric tube oil cooler is significantly less expensive than a plate type. If the system has sufficient cooling performance, the consensus is that you can substitute a good concentric tube design (with a low-pressure-drop turbolator) for a one or two-plate cooler. But how often is that going to come up? After all, a big percentage of oil cooler replacements are going to be dictated by component failure. However, if you’re just replacing rather than repairing a leaker, well then you may be able to consider the option. Whatever you do, you don’t want to be replacing an OE plate-type with an older-design concentric tube with a conventional turbulizer. That’s asking for trouble.

In addition, for quality-control purposes, there are spot tests for deformation and burst pressure, depending on the size and material of the cooler. An 1-1/2-inch brass concentric is tested for deformation and should reach or surpass 250 p.s.i., 350 p.s.i. before it bursts. A 1-3/4-inch concentric should reach 350 p.s.i. before it deforms, 500 p.s.i. before it bursts.

Aluminum has lower tensile and burst strength. Although it’s leak-tested at 100 p.s.i., a 1-3/4-inch concentric might be deformation-tested to 270 p.s.i. and tested to reach 350 p.s.i. before burst.

All pressure tests are made with shop air, not liquid.

Even if you have the capability of going past a shop air leak check at 100 p.s.i., don’t play quality control engineer. As the ads for high-speed driving say, “Do not try this yourself.” Incidentally, aluminum fittings are softer than brass or steel, so don’t over torque.

If you do agricultural work, you could be dealing with really beefy stuff. Some John Deere concentric tube oil coolers carry a burst pressure spec of 900 p.s.i., and actually are designed for 1100-1200 p.s.i. The ends are where the coolers are most likely to burst, but the Deere coolers get reinforcing plates to insure they surpass the specs.

In addition to fluid breakdown as a result of excessive heat, fluid which has been contaminated with coolant due to a leaking oil cooler is just as detrimental to the operation of the automatic transmission. If the fluid is a milky, pink color you need to flush the system completely. Coolant mixed in with transmission fluid causes the lining material on the clutch disks to flake off and the rubber seals will begin leaking, causing a drop in oil pressure to clutch packs. The result? Transmission failure.

The addition of an external, auxiliary oil cooler is always wise. Put it on and forget about most transmission overheating problems. If the vehicle is used for towing or heavy-duty operation, you need to choose the proper oil cooler for the application.

Auxiliary oil coolers are available from many aftermarket suppliers. Make certain to install a good quality product and follow the installation instructions to ensure maximum cooling and trouble-free operation.