Project LML has been a long process, but now, after a full year of ownership, it’s made quite the transformation from a run-of-the-mill, highmileage stock truck to the 600 hp trailer-towing monster you see now.
With upgrades to the tuning, turbo system, suspension, transmission and, of course, some cosmetic bolt-ons, there hasn’t been a load this truck couldn’t handle with ease. Running 80 mph and pulling 6th gear over 6 percent grades, towing the family travel trailer through the mountain ranges of Utah is basically a nonissue. The truck has all the power a guy could need, with more throttle always on tap.
However, on the hottest summer days, there has been one thing slowing us down: coolant temperatures. With the Promax 64 turbocharger and custom GDP tuning, the LML has an incredible power and torque curve that allows the truck to run any gear at any speed it wants while towing. Nevertheless, on long, strenuous, uphill pulls, the coolant temperatures have been known to climb north of 220 degrees. As of the next round of upgrades, the cooling system will be addressed to make it more efficient and effective while towing.
The truck has 130,000 miles on it now; and because I have no knowledge of any past cooling system services, replacing the antifreeze with new is the first big thing. Checking the exterior of the radiator for any blockages or debris buildup is the next step, and installing new thermostats would also be a good idea.
The system would be drained, so it was decided that upgrading the radiator to a better-flowing aftermarket unit could also help. On this model truck, the radiator comes out easiest as an assembly still attached to the intercooler, so we’ll be replacing that with a better-flowing unit as well.
The Mishimoto-brand radiator and intercooler is something we’ve featured in Diesel World Magazine before, and seeing great results from previous projects, it seemed the perfect option for Project LML and helping its coolant temperature troubles.
The direct-fit performance radiator is a full aluminum unit with a 100 percent brazed core that offers a 22 percent increase in capacity for better cooling efficiency. The Tig-welded core and end tanks offer great durability, and an added drain plug will make future coolant services easier and less messy.
With six years and 130,000 miles of wear and tear on the factory intercooler, hoses and thermostats, the Mishimoto silicone hose kit and low-temperature thermostats would also help increase
durability and cooling performance. The low-temp t-stat will open 5 degrees sooner than the factory unit, allowing the new radiator to start doing more work to keep coolant temps down sooner. All these upgrades should help us maintain more-constant and safer coolant temperatures under even the most extreme conditions.
While making some efficiency upgrades to the cooling system, we also opted to make some cosmetic upgrades—the addition of the fabricated and powder-coated factory replacement coolant tank and upper radiator hose from HSP Diesel. The factory coolant reservoir does its job, but it’s not the prettiest thing under the hood, especially after we’d installed HSP’S Max Flow candy-red-coated turbo piping kit. The CNC cut and bent aluminum coolant tank fits in the stock locations and includes all the fittings and hoses you need to clean up the engine bay. To go along with the new coolant reservoir, the HSP Upper Coolant Tube kit is also installed. While it does nothing for performance or cooling, it sure looks nice under the hood with the other powder-coated components!
Because the factory intercooler was removed from the truck while doing the radiator swap, along with the fact that this truck has had a turbocharger upgrade, it seemed logical to upgrade the intercooler while it was apart.
The Mishimoto aluminum intercooler uses a bar-and-plate core that is better at displacing heat in the charge air system; and the core is almost double the thickness compared to the stock unit. The better-flowing core allows air to flow through the system with less restriction, helping with air temperatures and reducing EGTS under load. The factory intercooler has a plastic end tank that could leak in high boost and performance applications, so the cast-aluminum end tanks on the Mishimoto unit will be more durable for a lot of applications, and it just makes more sense to install it now, should we ever decide to upgrade to compound turbos down the road.
The aluminum radiator from Mishimoto Automotive for the 2011–2016 LML Duramax offers better cooling efficiency from the improved core design. And when packaged together with its low-temperature thermostats, silicon hose kit and an HSP Diesel upper hose and reservoir, it offers excellent durability—and the looks to go with it.
Most trucks, including the LML Duramax, have a transmission fluid cooler built inside the radiator. So, along with the upper and lower radiator hoses being disconnected, the transmission cooler lines will need to be removed from the end tanks as well. This truck uses a simple, quick-disconnect-style coupler: When a small clip retainer is pulled out, the line will pull right out. Be sure to save the clip, because it and the fitting will be reused in the Mishimoto radiator.
The TCM will need to be unbolted and set aside, along with the upper fan shroud, radiator breather/ overflow hose and both transmission cooler lines. We’ll replace the upper coolant hose with the powder-coated hard line from HSP that will make a great match to our previously installed Max Flow turbo piping kit.
The complete cooling package swap will be accomplished by removing the radiator and the intercooler as a complete assembly. So, the hot- and cold-side intercooler tubes will need to be disconnected. Once the assembly is removed from the truck and on the shop floor, the two can be unbolted from each other.
On this model year, GM didn’t put a drain or petcock anywhere in the system; and because we’ll be replacing the lower radiator hose, we opted to just slice it at the lowest point. This allowed the system to drain without making a giant mess on the shop floor (just pulling the lower hose from the radiator would).
For thermostats, we opted to install the Mishimoto Low Temp units that will open and allow coolant to start flowing 5 degrees sooner than the factory thermostat. The lower-temp thermostat will help with overheating when towing under a heavy load in the summer months. Mishimoto also offers a high-temp set of t-stats for cold-climate guys who need to keep more heat in the engine.
With another set of hands to help, the radiator/intercooler assembly can be removed and reinstalled in the truck as a complete assembly. The combo is extremely cumbersome and will be tough to fish in and out on your own— especially if you’re trying to keep any antifreeze left over in the core from spilling out everywhere.
With the intercooler out of the way, you can get a good look at the front and back sides of the radiator core. Notice all the dirt and debris that has built up on the outside just from driving? This restricts airflow and can cause higher-than-normal fluid temperatures, especially under hard load.
With the complete cooling system drained, this was the perfect time to replace the factory thermostats. The truck now has 130,000 miles on it, so it seemed a no-brainer to just replace it with a new one at this point. It’s only an extra 10 minutes of work to remove the t-stat housing from the top of the engine.
Looking to make future coolant system services easier and less of a mess, Mishimoto welded a drain into the lowest point of the radiator. The plug also has a magnet to catch any metal debris that might be circulating through the system.
When they are sitting side by side on the shop floor, it is obvious how much larger the Mishimoto intercooler is compared to the stock unit. At nearly 3 inches thick, the new cooler is 73 percent thicker, which means more surface area and better cooling. This unit works great for factory horsepower levels but is also a must-have for big boost and high-volume performance builds running large singles or even compound turbos.
While there was nothing wrong with the factory coolant tank, in some trucks, the stock bottle can get quite dirty inside from cooling system contaminants or get yellow over time. Because a Max Flow turbo piping kit from HSP Diesel had previously been installed on the truck, the company’s stock replacement fabricated overflow tank made for a nice upgrade to go along with it.
The matching upper radiator line also makes for a nice look under the hood and ties everything together nicely. The factory coolant hose was still in good shape, but the candy-red powder coat and black-coated hose clamps match the turbo kit and add some nice pop under the hood.
Engineered as a direct drop-in unit, the radiator couldn’t be made any larger than the factory unit and still fit without rubbing. But Mishimoto engineered, and uses, a much more efficient core for better cooling capacity and fluid flow across the core. The end tank design is also optimized for better efficiency.
Mishimoto’s replacement intercooler uses durable cast end tanks with a more efficient bar-and-plate core designed to improve airflow and lowercharge air temperatures for better engine efficiency and lower Egts—perfect for a truck used for heavy towing at higher horsepower levels.
The cast-aluminum end tanks reduce the chances of a weld splitting or leaking and also allow for better longevity and durability. The core design offers a 101 percent increase in volume capacity, so more air can get through and cooled, making the system more efficient than stock.