The big change in the 2020 Duramax L5P is not a mystery power part. It is heat management. To move towing capacity up to 35,500 pounds, GM had to make sure the engine could keep delivering its rated 445 horsepower and 910 lb-ft under real load, not just on an engine dyno. That is why the front drive changed. The fan now gets its own belt plane, driven from the rib side for better grip, and the fan itself grows to 28 in.. Combined with a larger cooling package, that gives the truck more ability to pull air through the radiator when altitude, grade, and trailer weight all stack up against it. The oil side got real attention too. The L5P oil cooler now has 36% more cooling surface area, revised fin design, and a taller outlet path that improves how oil moves through the stack instead of favoring the bottom of the core. GM also increased piston cooling nozzle size. Put together, those changes are about keeping oil temperature under control and protecting the hard parts when the engine is held at power for long stretches. There is another takeaway here: the stock turbo inlet is doing more than feeding air. Its shape supports the compressor recirculation system and the crankcase ventilation connection. Replace it with simple constant-diameter tubing and you can create oil-control and surge problems. The 2020 L5P shows what matters when a diesel has to work for real: airflow, oil cooling, and durability under sustained load.
Gale Banks opens by explaining that he recently visited GM Global Propulsion Systems in Pontiac, Michigan, where he was briefed on the updated 2020 Duramax L5P. He has two of the engines on hand for inspection and testing. The central question is why GM revised the engine for 2020 and what changes were necessary to support the truck's increased towing capability.
According to Banks, the 2020 trucks were upgraded so they could pull trailers weighing up to 35,500 pounds. His purpose is to walk through the engine changes that make that possible, focusing on the hardware revisions that improve sustained cooling, durability, and heavy-load operation rather than simply peak dyno output.
Banks begins with a walkaround of an engine in factory-shipped form, noting that the most obvious difference is at the front of the engine. Earlier L5P versions used a single belt plane, but the 2020 engine adds another belt plane and an additional pulley dedicated to driving the fan. That change immediately signals a major increase in cooling-system capability.
He also points out a feature that is not new but still noteworthy: the L5P uses a much more substantial block heater than the earlier LM and LS engines. For cold-weather operation, he considers it a serious block heater. Around the rear of the engine, most components remain familiar, although GM made some subtle revisions, including a new coolant degassing pipe. Banks believes the coolant recovery bottle is also relocated in the truck installation. The turbocharger still uses a motor-driven, very fast-reacting variable geometry control system, which improves response and helps with emissions calibration. On the example engine, the catalytic converter normally mounted at the back of the turbocharger has been removed so the turbo hardware is easier to see.
The change that stands out most to Banks is the engine oil cooler and the ducting into and out of it. He explains that in prior Duramax development work, including Banks' JLTV military engines and Banks Max prototype builds, he had experimented with oil coolers using more plates to increase capacity. Even so, he had never been satisfied with the fluid dynamics of the housing design used on earlier versions.
For the 2020 L5P, GM revised the cooler substantially. Compared with the 2017 through 2019 arrangement, the new cooler adds plates and uses a new fin design. Banks states that the result is 36% more oil-cooling surface area. Just as important, GM changed the flow path. On the earlier setup, oil entered and exited at the bottom of the stacked cooler, which limited how effectively the upper portion of the stack was used. The new design angles the top of the cooler so the fluid enters low and exits high, improving how oil moves through the core. To support that routing, the outlet casting from the cooler to the block is taller. In Banks' view, the combination of 36% more plate area, improved fins, and better internal flow could yield roughly 45% more oil heat rejection. For an engine expected to stay under heavy load for long periods, he considers that a major improvement.
Banks notes that the engines he is showing are preproduction 2020 L5Ps. At the time of filming, he says the Duramax plant was expected to convert to 2020 production in April, with truck production likely beginning in May. He already has one of the engines in a dyno cell and intends to push it hard to determine its limits.
That testing is framed as a durability and engineering exercise rather than a short-term stunt. Banks emphasizes that his interest is in understanding how far the revised engine can be taken while maintaining oil supply, cooling, and structural integrity. He presents the 2020 hardware changes as a stronger starting point for that work.
Banks then turns to the turbocharger inlet and warns against oversimplified aftermarket intake-pipe modifications. He notes that many builders replace the factory inlet tube with steel tubing or ordinary muffler tubing, but he argues that this area is more complex than it appears.
The factory air inlet is large at the compressor side and includes a shaped transition with an air gap between two sections. That geometry allows the compressor recirculation anti-surge system to function correctly. If someone removes the factory piece and substitutes a constant-diameter 3.5-inch tube with a flange, Banks says that person defeats the intended operation of the recirculation system.
He also stresses that the crankcase venting system feeds into this inlet hose, and that the pressure in that line must be correct. The angle at which the vent enters the airflow, along with the internal shape of the inlet, affects how the system behaves. In his experience, those details cannot be duplicated easily with constant-diameter tubing. Banks says he knows this from spending thousands of hours developing a new crankcase system for the L5P and dealing with the same issues at higher power levels. If the inlet and venting geometry are handled incorrectly, the engine can push oil into the turbocharger intake.
The added belt plane is tied directly to the cooling upgrades. Banks explains that the new belt arrangement exists primarily to drive the fan. On the 2017 through 2019 L5P, the vibration damper used a single six-groove belt plane. For 2020, GM added a bolt pattern to the front of the damper and attached a separate drive for the fan.
Banks points out that this fan belt is substantially wider than the belt system driving the rest of the accessories. In his estimation, the horsepower required to drive the fan under maximum demand may exceed the power needed for the dual alternators, air-conditioning compressor, and other accessories combined. That does not mean the fan consumes that power continuously, because the system uses a fan clutch, but it shows how serious the cooling requirement is.
He also compares the fan-drive geometry. On the earlier arrangement, the fan had to be driven from the back side of the belt to achieve the correct rotation, which is why the sheave was flat. On the 2020 setup, the fan is driven from the ribbed side of the belt instead. Banks says this provides a better coupling. The system also uses its own spring-loaded idler, a heavy-duty bearing arrangement, and completely new front covers compared with earlier L5P engines.
Banks ties the fan-drive changes to the real challenge of towing: not making rated power briefly, but delivering it continuously. The engine is rated at 445 horsepower and 910 pound-feet, but the issue is whether that output can be maintained under real towing conditions. He describes this as the difference between engine-dyno numbers and the power and torque a truck can actually put to the ground for extended periods.
The problem becomes more severe at altitude. As a truck climbs grades while towing heavy loads, air density drops. Lower-density air passing through the radiator absorbs less heat, so the engine becomes harder to cool just when the drivetrain is being asked to sustain high output. GM's answer, as Banks describes it, is a much larger cooling package and a 28-inch fan, two inches larger than before. Combined with the fan clutch, that gives the truck more airflow capacity when needed without imposing the full parasitic load all the time.
Banks sees this as a serious upgrade for mountain towing. The 10-speed transmission can keep the engine in a range where it can continue making full torque in the lower gears, but that only matters if the cooling system can support sustained operation. In his view, the 2020 revisions are aimed squarely at that requirement.
To explain why these cooling changes matter, Banks contrasts sustained-load engineering with short-duration power demonstrations. He refers to the kind of testing Banks performs on military engines, including a 400-hour NATO test in which the engine spends 85% of the time either at full power for two hours or full torque for two hours, repeating in 10-hour cycles and then repeating those cycles 40 times.
His point is that real durability work is about making power live under continuous stress, not producing a dramatic failure after a few seconds at extreme output. He places GM's 2020 L5P revisions in that same context. The larger fan system and improved oil cooling are not just about headline numbers; they are about allowing the engine to remain at high load for longer periods without overheating or degrading the oil.
Banks also inspected the water pumps to see whether GM had increased impeller diameter or impeller height for 2020. He reports that the early L5P and the 2020 L5P water pumps are essentially identical, in fact exactly the same by his inspection. That suggests GM concentrated its cooling improvements elsewhere, particularly in airflow and oil-temperature control.
Looking ahead to his dyno program, Banks says the revised engine gives him a strong foundation for finding the limits of the pistons, block, crankshaft, and connecting rods. He notes that the 2020 package includes not only the larger oil cooler but also bigger piston-cooling nozzles. His expectation is that the engine will be harder to starve for oil and easier to keep cool under aggressive testing.
He plans to rev the engine somewhat higher and, if necessary, add further support systems such as a second belt-driven water pump or even a second belt-driven oil pump. Those modifications would be part of the dyno development series rather than the stock-engine overview. His conclusion is that the 2020 Duramax L5P arrives with meaningful hardware changes aimed at sustained heavy-duty performance, and that those changes make it an especially interesting platform for further testing.