When a Duramax is worked hard and held under load, oil has to carry away a lot of heat. That makes the oil cooler a real limit point, not just a packaging detail. The 2020 L5P cooler stands out because GM added more cooling plates and appears to have improved the coolant path through the housing. Compared with earlier assemblies, the 2020 unit uses 19 plates instead of 14 on the 2017-2019 L5P and 11 on the 2001-2010 style cooler, with a larger internal opening and a higher outlet that should move coolant through more of the stack. That does not automatically make it the right upgrade. The real question is whether it can cut oil temperature without adding too much pressure drop through the cooler or filter. That is why the filter mount, bypass strategy, and housing flow path matter. The 2020 assembly also uses a smaller oil filter and appears to rely on the correct filter bypass arrangement, so filter choice becomes critical. If the fit and pressure-drop numbers check out, this later cooler looks like a serious upgrade path for earlier Duramax engines.
Gale Banks opens a newly delivered 2020 Duramax oil cooler and frames the inspection around a specific engineering question: what changed for 2020, and can the newer cooler be retrofitted onto earlier Duramax trucks? The packaging itself is unremarkable aside from the oversized outer box, but the important point is that the cooler arrives without instructions, implying it is intended as a service part rather than a consumer-oriented upgrade kit.
From the start, the evaluation is not about appearance. Banks is looking for functional changes in cooling capacity, oil-flow behavior, and physical compatibility with previous engines. The small size of the 2020 filter mount stands out immediately, raising questions about filter selection and flow capacity even before the cooler is disassembled and compared.
Banks explains that the 2001 through 2010 Duramax engines-LB7, LLY, LBZ, and LMM-use the same oil cooler and oil filter assembly. He then compares those earlier units with an early L5P cooler from the 2017-2019 model years and the revised 2020 L5P cooler.
The reason for the redesign appears tied to the 2020 truck's substantially increased towing capability. Although the L5P's rated horsepower stayed the same and peak torque increased by only 5 lb-ft, Banks believes GM made a significant cooling-system upgrade to support sustained heavy-load operation. In his view, higher tow ratings require more than peak power; they demand enough radiator capacity, fan performance, inlet air area, oil-pump capacity, and especially oil-cooling capacity to reject heat continuously when the engine is held near rated output for long periods.
The most obvious hardware change is in the cooler core itself. Banks compares the stacked-plate oil cooler assemblies across generations and counts the number of cooling plates in each design. The early cooler used from 2001 through 2010 has 11 plates. The 2017-2019 L5P cooler increases that count to 14 plates. The 2020 L5P cooler jumps again to 19 plates.
He also notes that the 2020 plates appear thinner than those in the earlier assemblies, but there are many more of them. That suggests a substantial redesign rather than a minor revision. The oil still flows through the stacked plates while engine coolant flows through the surrounding housing, but the increased plate count indicates a much larger heat-transfer opportunity. On that basis alone, Banks sees the 2020 cooler as a major improvement over both the 2017-2019 version and the older 2001-2010 design.
Banks pays close attention not just to plate count but to how coolant enters and exits the housing. He says the inlet location appears identical when comparing the housings and bolt-hole positions, which is encouraging for retrofit potential. However, the internal opening into the earlier housing is noticeably smaller, while the later design provides a much larger entrance into the cooler body. That points to improved coolant flow into the assembly.
The outlet-side redesign is even more important. On the earlier housing, the coolant exit remains relatively low and close to the block, which suggests that the upper portion of the plate stack may not receive strong coolant flow. In Banks' view, that means some plates above that level may not be used effectively. On the 2020 cooler, the outlet has been moved upward, forcing coolant to travel more completely through the assembly before leaving. He believes the plate arrangement was likely revised to take advantage of that new flow path, and his visual inspection supports that conclusion. Taken together, the larger inlet and improved outlet routing make the 2020 housing look substantially better from a coolant-distribution standpoint.
Banks says his evaluation will ultimately focus on two measurements: oil-temperature reduction through the cooler and oil-pressure reduction through the cooler. The ideal design lowers oil temperature as much as possible while imposing as little restriction as possible on the lubrication system.
A larger cooler might be expected to produce less pressure drop, but Banks does not assume that automatically. Because the 2020 unit uses thinner plates and a denser stack, he wants actual test data rather than visual impressions alone. His goal is minimum pressure drop through both the oil filter and the cooler, combined with maximum oil cooling. That balance matters because a cooler that rejects more heat but restricts oil flow excessively could create lubrication concerns under load.
Physically, the 2020 cooler looks promising as a retrofit candidate for earlier trucks. Banks says the inlet geometry and bolt-hole locations appear identical, which suggests the assembly may bolt onto previous Duramax applications. Even so, he emphasizes that the first practical step will be confirming that the larger 2020 unit clears surrounding components in earlier engine bays and does not interfere with anything once installed.
He also identifies one likely requirement for adapting the newer cooler to an earlier block: the 2020 elbow and seal assembly. Because the coolant outlet arrangement changed, the newer elbow appears necessary to make the revised housing work correctly. That means the retrofit may not be a simple cooler-only swap, even if the main mounting pattern is shared.
The filter arrangement changed significantly for 2020. All earlier Duramax applications through 2019 use an AC Delco PF2232 oil filter. The 2020 cooler uses a smaller filter, and Banks is immediately cautious about that change. He does not yet draw a final conclusion, but he is concerned about whether the smaller filter compromises flow area or filtration capacity relative to the earlier setup.
That concern ties directly into his broader objective of minimizing pressure drop. Even if the cooler itself is improved, a smaller filter mount could become a bottleneck. Banks says he may investigate ways to get more oil filter capacity onto the 2020 assembly, but at this stage he leaves that as an open question pending further examination and testing.
Banks also compares the bypass or check-valve strategy used in the oiling system. On earlier Duramax engines through 2019, the system effectively includes two bypass paths in parallel: one built into the oil filter and another built into the oil cooler assembly. The purpose is protection against restriction. If the cooler becomes plugged or pressure drop rises too high, the cooler bypass can open. Likewise, the filter itself includes an internal bypass valve so that if the filter becomes clogged, oil flow to the bearings is not completely cut off.
He interprets the dual-bypass arrangement as a safeguard against incorrect service parts. If someone installs the wrong oil filter-specifically one without the proper bypass valve-the cooler assembly still provides a secondary protection path. On the 2020 unit, Banks does not see that secondary check valve in the cooler assembly. Combined with the revised filter mount, that suggests GM changed its approach and may now rely more heavily on the correct filter being installed. His practical conclusion is straightforward: on the 2020 configuration, using the proper oil filter is especially important.
Banks' preliminary verdict is that the 2020 Duramax oil cooler looks substantially improved. The 19-plate stack, larger coolant entrance, and relocated outlet all suggest better oil-cooling performance than the 14-plate 2017-2019 cooler and the 11-plate 2001-2010 design. At the same time, the smaller filter mount and revised bypass strategy introduce new questions that cannot be answered by visual inspection alone.
He plans to resolve those questions through testing in the Killing a Duramax series, where the 2020 cooler will be compared directly against the 2017-2019 version. The key outcomes he wants to measure are how much oil temperature each cooler removes and how much pressure drop each one creates. Until those results are in, his assessment remains provisional, but his initial impression is clear: the 2020 cooler appears to be a serious upgrade and a potentially valuable retrofit if fitment and flow concerns check out.