Cummins Cooling Mods

Keeping EGT and Coolant Temps in Check in A Modified 6.7L Cummins

With 800 lb-ft of torque or more on tap and a stack of massive heat exchangers onboard, it’s no wonder modern diesels perform so well straight from the dealership. But what happens after we’ve doubled the factory horsepower rating? Are we still safe to tow the same 12-to-15 tons we did when the truck was bone stock? Believe it or not, the answer is both yes and no. While the factory intercooler can suffice, with hundreds more ponies in the mix, it usually means we’re watching gauges more than we’re watching the road or that we’re forced to hold back the horsepower reins while climbing grades.

Upon adding a PowerFlo lift pump and S467.7 (by way of a second-gen turbo swap kit) from Fleece Performance Engineering, the ’12 Ram 2500 shown here was making a dyno-proven 570 hp and 1,140 lb-ft at the wheels. However, even with the stock injectors and CP3 still in the mix, the owner was seeing EGT crest 1,500 degrees on prolonged pulls. To cool the 6.7L Cummins off, he reached out to the cooling experts at Mishimoto for a full intercooler kit. Then, for added peace of mind when working the truck hard, one of Mishimoto’s performance radiators was bolted in place of the stocker.

During our half-day install, the direct drop-in radiator fell into place within minutes, while a few massaging measures were required in order to accommodate the massive, 100-percent thicker Mishimoto intercooler. With a 190-degree drop in EGT and lower coolant temps when all was said and done, we think the results speak for themselves.

First things first, we positioned a 5-gallon bucket under the ’12 Ram 2500’s radiator and started draining the original Mopar coolant. With 108,000 miles on the truck, and Cummins’ coolant flush service interval being 97,500 miles (or 60 months) on ’07.5-’12 6.7L engines, the time had come to start with fresh antifreeze.
Underneath the truck, the four pop clips that hold the plastic under tray in place were removed. A pair of hose clamp pliers then made quick work of the upper and lower radiator hoses. Then we removed the bolts that hold the radiator fan shroud in place, unplugged the fan harness, loosened the fan nut, and pulled the fan and shroud at the same time.
Next, the overflow hose was disconnected from the radiator and the two bolts securing the radiator to the core support were removed. After that, the radiator was pulled, with the leftover coolant trapped inside it drained and disposed of properly.
As you can see here, retaining the same basic overall dimensions helps make the Mishimoto radiator the direct, bolt-in replacement unit that it is on ’10-’12 Rams. Because of its similarity in size, the install is, in Mishimoto’s own words, effortless.
With both the factory radiator and Mishimoto unit positioned side by side, the difference in core thickness was obvious. The Mishimoto radiator’s core measures 1.95 inches vs. the factory radiator’s 1.7-inch dimension. But in addition to the increased core thickness, the Mishimoto unit features bigger coolant tubes for added fluid capacity. All told, the Mishimoto radiator increases coolant capacity by nearly a gallon.
Another area of improvement over the factory radiator lies in the fins. The Mishimoto unit’s cooling fin area is 13 percent larger than stock, and the aforementioned coolant tubes measure 9 percent larger than OEM. These cooling fin and tube enhancements are the real key behind the Mishimoto radiator’s ability to reduce coolant temps and improve heat transfer.
Unfortunately, there is no way around having to disconnect the A/C lines in order to install the Mishimoto intercooler. This part of the install requires that you have access to either proper A/C equipment or a shop experienced in A/C repair or servicing.
While waiting on the A/C system’s refrigerant to be evacuated, we went ahead and removed the thermostat housing. Like the coolant flush interval, the thermostat on the ’07.5-’12 6.7L Cummins should also be changed every 97,500 miles. The mating surfaces of the thermostat housing and the head were both cleaned up via die-grinder and Scotch-Brite pad before being reinstalled.
A common thermostat upgrade on ’10-‘12 Cummins mills is to ditch the factory 200-degree unit in favor of a 180-degree thermostat. The lower temperature thermostat opens sooner, which is helpful in modified trucks that make more horsepower, see higher rpm, and are subjected to toastier EGTs.
Removal of the factory intercooler is a bit more involved than pulling the radiator. We got started by removing the grille, dismounting the hood latch mechanism, and breaking the horn assembly free.
The factory A/C condenser and transmission cooler (the two are married together in a single heat exchanger) have to be removed as well. With the A/C system fully evacuated, the lines were disconnected and the condenser/transmission cooler’s mounting bolts were removed. Then the heat exchanger was completely freed from the truck.
With the truck’s upper core support out of the way, the factory intercooler could be removed without pulling the front bumper. But, as we found out the hard way, the bumper does indeed have to be pulled in order to get the new, thicker Mishimoto intercooler into place.
In terms of overall height and width, the Mishimoto intercooler’s measurements are comparable to the factory unit. However, the inlet and outlet diameter is increased from 3 inches to 3.5 inches. The cast-aluminum, 4mm thick end tanks on the Mishimoto intercooler are also strategically designed for optimum internal airflow as well as superior external aerodynamics.
Mishimoto’s performance intercooler is available in either Sleek Silver or Stealth Black (shown here). Its internal fins are designed to promote maximum heat transfer but also a very minimal boost pressure drop. This keeps the entire induction system efficient in addition to lowering intake air temps and EGT.
Notice the difference? The Mishimoto intercooler’s bar and plate core thickness is 3.15 inches—100-percent thicker than stock. Its massive core width is the cause for pulling the front bumper in order to install it, but for the significant cooling it provides it’s definitely worth it.
Complementing the intercooler upgrade (and also working in conjunction with the larger inlet and outlet) is Mishimoto’s intercooler pipe and boot kit. The mandrel-bent hot- and cold-side intercooler pipes are polished to a mirror finish, and the cold-side pipe measures 3.5 inches (the hot-side pipe measures 3 inches). The accompanying boots feature Mishimoto’sDuraCore technology, a synthetic material that provides unmatched resistance to heat, pressure, and oil. Constant tension T-bolt clamps round out the complete package.
Because the intercooler and radiator were out of the way, we went ahead and installed the Mishimoto cold-side intercooler pipe at this time. The supplied boots and clamps worked seamlessly with the truck’s existing GDP intake elbow.
Utilizing the mounts welded to the Mishimoto intercooler’s end tanks, the intercooler was dropped into the same location the factory unit resided in (perched on the front cross member). Vibration transfer through the cross member is quelled through the use of rubber isolator pads.
Once the intercooler was in place, the truck’s previously-removed upper radiator core support section was reinstalled. Then the intercooler mounting bolts were installed, securing it to the upper core support.
Next up, the A/C and transmission cooler was reinstalled, its brackets allowing it to be bolted directly onto the new intercooler. Then the transmission lines and their respective retaining clips were reconnected.
Lowering the Mishimoto radiator into place proved uneventful. After the factory rubber grommets for the upper mounting points were swapped over to the Mishimoto unit, it was simply a matter of bolting it into place behind the intercooler (two 13mm bolts up top and two 10mm bolts below). Then the fan and fan shroud were reinstalled and the fan harness plugged back in.
Because we planned to switch over to Valvoline Zerex Extended Life coolant, we wanted to remove as much of the factory coolant from the system as possible. Using a manual fluid extractor pump, we pulled all of the remaining coolant out of the degas bottle.
After reinstalling the upper and lower radiator hoses and their respective clamps, the overflow hose from the degas bottle was attached to the radiator. Then the 19-psi radiator cap was removed in preparation for adding coolant.
A compatible alternative to the factory antifreeze (Mopar PN 68048953AB), Valvoline’s heavy-duty Zerex Extended Life coolant offers guaranteed protection for 3 years or 300,000 miles. And, with the addition of a coolant life extender the 50/50 diesel-ready mixture is rated for 6 years, 14,000 hours, or 600,000 miles (whichever comes first).
With the coolant topped off, the engine was started, inspected for leaks, and the truck’s heat cranked on to help bleed any leftover air bubbles from the system. Once the truck was up to operating temp, the cooling ability of the new intercooler was put to the test. The result? When running the same rolling-start, wide-open throttle tests that yielded 1,522 degree EGT the day before, EGT now peaked at 1,334 degrees—nearly a 200-degree reduction.


Before and After Intercooler Testing

Factory Intercooler
EGT Flat Ground Cruising at 70 mph: 790 degrees F
EGT Peak (WOT): 1,522 degrees F

Mishimoto Performance Intercooler
EGT Flat Ground Cruising at 70 mph: 730 degrees F
EGT Peak (WOT): 1,334 degrees F



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