The 3.0 Duramax Goes to Sea: Why the OXE Marine + GM Deal Is Good News for Owners

When news broke that OXE Marine and GM Marine had signed a development agreement to use Duramax engines in a new generation of diesel outboards, most people saw it as a marine story. For 3.0 Duramax owners, it is something else entirely:

It’s a strong signal that GM sees the LZ0 3.0L Duramax inline-six as a long-term platform, not a short-lived experiment.

In this article, we’ll break down what the agreement actually says, why it matters for truck and SUV owners, and how a marine version of the LZ0 will likely differ from the one under your hood—especially around cooling and emissions.

What OXE and GM Actually Announced

On November 13, 2025, OXE Marine AB announced a supply and development agreement with GM Marine. In that agreement: (Inderes)

• GM Marine becomes OXE’s future supplier of advanced powertrain solutions.

• OXE becomes an official GM Integrator, with access to GM’s engine portfolio.

• The collaboration launches with GM’s Duramax engine family, adapted to OXE’s patented high-torque belt-driven transmission system for outboards. (Inderes)

• The initial focus of the deal is the Duramax LZ0 3.0 inline-six, which OXE and GM will bring to the marine market in both outboard and inboard configurations. (Inderes)

On GM’s side, the LZ0 is already listed on GM Powered Solutions as an engine offered for marine, on-road, off-road and industrial applications. It’s rated at:

• 305 hp @ 3,750 rpm

• 495 lb-ft (671 Nm) @ 2,750 rpm, with about 94% of that torque available by 1,500 rpm

• 15.2:1 compression, steel pistons, updated injectors and turbo, and a 200,000-mile validated oil pump belt

  
  

In other words: the same basic engine architecture used in late-model Silverado/Sierra 1500 and GM full-size SUVs is now being positioned as the heart of a commercial-grade marine package.

Why This Is Good News for 3.0 Duramax Owners

This agreement doesn’t just mean “a Duramax in a boat.” It has real implications for owners of 3.0-equipped trucks and SUVs.

1. It signals long-term commitment to the LZ0 architecture

Companies don’t casually expand a dead-end engine into new sectors. OXE and GM are building a new generation of commercial outboards around the LZ0, aimed at professional users with “demanding needs.” (Inderes)

That implies:

• GM expects the LZ0 to be around for years, with parts and engineering support continuing well into the future.

• The engine is now part of a broader multi-sector strategy: pickups, SUVs, industrial equipment, and now marine.

For owners, that is exactly what you want to see: an engine family being pushed into more markets, not quietly dropped.

2. Marine duty is a brutal proving ground

OXE’s current diesel outboards, like the OXE300, are built around a 3.0L inline-six diesel (BMW-based) and tuned for 300 hp and up to 945 Nm (697 lb-ft) of torque at the prop shaft, with 30–40% fuel savings vs comparable gasoline outboards. (oxemarine.com)

These engines are used on:

• Workboats

• Patrol and governmental craft

• Commercial fishing and charter vessels

That kind of usage means high load for long periods, not just short bursts of acceleration like a pickup on the highway. The fact that GM is willing to put the LZ0 into this environment suggests confidence in its:

• Bottom-end strength

• Cooling capacity

• Long-term durability under continuous load

If an engine is trusted to push a loaded workboat all day, pushing a half-ton truck around is not the limiting case.

3. More engines built usually means better long-term parts support

The more places an engine appears, the harder it is for the manufacturer to walk away from:

• Replacement parts tooling

• Software and calibration support

• Core engineering resources

With the LZ0 now serving both land and sea, GM has a stronger business case to keep building and supporting it than if it only lived in a handful of truck trims.

How a Marine LZ0 Will Differ from Your Truck’s 3.0

The engine family is the same, but a marine LZ0 will not be a copy-paste of the pickup version. Some changes will be obvious; others are more speculative based on how marine engines are typically built.

1. Cooling: likely no complex coolant flow control valve

In light-duty trucks and SUVs, the 3.0 Duramax uses a multi-port coolant flow control valve to juggle:

• Fast engine warm-up

• Cabin heat

• Transmission and EGR cooling

• Aftertreatment temperature management

That valve lives deep in the valley and has been a known failure point for some owners.

Marine engines are cooled differently. Outboards like the existing OXE300 use: (oxemarine.com)

• A closed coolant circuit on the engine

• A raw-water heat exchanger, pumping lake or seawater through a cooler to pull heat out

• A simpler plumbing layout focused on continuous, predictable high-load operation

Speculation, based on typical marine design:

It is very likely that the marine LZ0 will use a simpler coolant routing and heat-exchanger setup, without the same valley-mounted coolant flow control valve used in the trucks. The marine package simply doesn’t need to juggle cabin HVAC, underbody aftertreatment warm-up, and all the other tricks required by on-road emissions cycles.

We will have to see the final schematics to confirm the exact plumbing, but from an engineering standpoint, a cleaner, more conventional cooling system is the logical choice at sea.

2. Emissions: same mission (clean air), completely different hardware

On-road LZ0 (your truck) is calibrated for light-duty vehicle standards and uses a full aftertreatment stack: GM lists the system as including: (GM Powered Solutions)

• Close-coupled diesel oxidation catalyst (CCDOC)

• Diesel particulate filter integrated with SCR (SCRF)

• Additional SCR and ammonia slip catalyst

• High- and low-pressure EGR

Marine engines fall into a different rulebook:

• In the U.S., commercial marine diesels are regulated under 40 CFR Part 1042, which defines Tier 3 and Tier 4 standards for different power categories. Tier 4 (with mandatory SCR/DPF-type aftertreatment) currently applies mainly to engines above 600 kW (~800 hp).

• Internationally, marine NOx limits are governed by IMO MARPOL Annex VI, with Tier II and Tier III levels depending on vessel age and where it operates. Tier III typically requires SCR in Emission Control Areas, while Tier II can be met with in-cylinder measures and simpler exhaust treatments.

  
  

OXE’s current outboards, including the OXE300, are advertised as compliant with EPA Tier III and IMO Tier II, with no public mention of DEF tanks or DPF canisters. (oxemarine.com)

Speculation, clearly labeled:

• For a 3.0L, ~300 hp commercial outboard:

  • It is plausible that OXE and GM will meet applicable marine Tier 3 / IMO II requirements using:

    • Clean combustion

    • High-pressure common-rail injection

    • Possibly an oxidation catalyst

  • That would not necessarily require a full truck-style DOC + DPF + SCR + DEF layout.

So while the pickup version of the LZ0 carries a complex aftertreatment system to meet light-duty Tier 3 vehicle rules, the marine version will likely have a simpler, duty-cycle-specific emissions solution tuned for steady high-load operation and different test cycles.

3. Mounting, drivetrain, and prop gearing

A few more differences that matter on the marine side:

• Horizontal engine, belt-drive leg OXE’s platform mounts an automotive-style inline-six horizontally and uses a belt-driven reduction gearbox to send torque down to the propeller. This allows larger prop diameters and high torque at low rpm. The OXE300, for example, delivers up to 945 Nm (697 lb-ft) at the prop shaft and runs a big prop at relatively low engine speed. (oxemarine.com)

• Continuous-duty calibrationYour truck spends a lot of time at partial load and varying rpm. A commercial outboard spends a lot of time close to a single cruise rpm under heavy load. Expect changes in:

  • Torque management

  • EGT limits

  • Cooling fan and pump strategies

  • Potentially even maximum rated power vs continuous power

• Electrical system and accessoriesOXE’s documentation highlights high alternator output (around 180 amps on the OXE300) and special considerations for aluminum/steel hulls and stray current corrosion. (oxemarine.com) A marine LZ0 package will be wired and grounded to marine standards, not pickup-truck body ground strategies.

  
  

Why This All Matters Back on Land

Stepping back from the technical details, here is the simple takeaway for a 3.0 Duramax owner:

1. GM is investing in the LZ0 beyond pickups.The engine is now part of GM’s Powered Solutions lineup and the centerpiece of a new commercial marine partnership. That points to a multi-year support horizon. (GM Powered Solutions)

2. The engine is being trusted in harsher duty cycles.Commercial boats put long, steady, high loads on engines. If the LZ0 is being tuned and validated for that world, it reinforces confidence in its core design for towing, hauling, and high-mileage truck use.

3. Marine design choices hint at what’s really necessary.A marine LZ0 will almost certainly do without some of the complex on-road support hardware, like the multi-port coolant flow control valve and truck-style aftertreatment stack. That doesn’t directly change your truck, but it is a reminder that:

   • The core engine is robust enough to stand on its own.

   • Many of the problem components owners talk about are there to satisfy a specific set of on-road regulations and packaging constraints, not because the basic engine is fragile.

     
     

Final Thoughts

The OXE Marine + GM Marine development agreement is more than a niche marine press release. It is a public statement that GM sees the 3.0L Duramax LZ0 inline-six as a capable, flexible, and long-term platform worthy of investment in demanding commercial environments.

For those of us driving 3.0 Duramax-equipped trucks and SUVs, that is exactly the kind of news we want to see:

• An engine architecture being expanded, not retired.

• Real-world validation in harder duty cycles than a typical half-ton pickup will ever see.

• A likely marine implementation that drops some of the failure-prone support hardware we deal with on the road.

As more technical details on the marine LZ0 package are released—cooling schematics, emissions layout, power curves—it will give us even more insight into what this engine can do when it is freed from light-duty vehicle regulations and put to work in a different world.