Search for “tanker engine” and one of the first results is a photo of a 14-cylinder diesel that weighs over 2,300 tonnes and makes more than 100,000 hp. It’s a magnificent machine. It’s also not a tanker engine. It was designed for large container ships, and the first 14-cylinder unit went into a container ship in 2006 (Wärtsilä RT-flex96C).

The engine in a real VLCC is smaller, slower and more interesting if you’re the one who has to keep it running. At the same time, it’s being asked to do more: burn less fuel, meet stricter emission rules, and stay within the power limits many tankers now run with.

This guide covers which engines tankers use at each size, why they’re built the way they are, what else runs in a tanker engine room, and which parts wear out. It skips most of the history.

What engine does an oil tanker use?

The main engine on a tanker is a two-stroke crosshead diesel. It’s large, slow and long-stroke, and it’s bolted directly to the propeller shaft. There’s no gearbox and no clutch: when the engine turns at 75 rpm, so does the propeller.

Two design families dominate the market:

• Everllence B&W (formerly MAN B&W): the G, S and ME-C engines, plus dual-fuel versions. Everllence covers tankers from small coastal vessels up to ULCCs (Everllence).
• WinGD: the X engines, the successor to the Wärtsilä and Sulzer two-stroke line.

Most of these engines aren’t built by Everllence or WinGD. They’re designed there and built under licence by engine works in Korea, China and Japan, usually close to the shipyard. That detail matters later, when you order parts.

Why two-stroke and not four-stroke?

Big question, but the short answer is propeller efficiency. A large propeller turning slowly moves a lot of water efficiently. A two-stroke engine can run at the propeller’s own speed, so it can drive it directly.

The numbers make the point. In an Everllence study of a 47,000 dwt MR tanker at 15.1 knots, moving from a 5.9 m propeller at 127 rpm to a 6.7 m propeller at 100 rpm cut the required engine power from 9,960 kW to 9,310 kW (MAN Energy Solutions, 2019). Same ship, same speed, 650 kW less. That’s why modern “ultra-long-stroke” engines exist: a longer stroke lets the engine turn more slowly and swing a bigger propeller.

Four-stroke diesel engines do appear on tankers, but mostly as auxiliary engines for power generation, on small coastal tankers, and in the electric propulsion of some gas carriers.

How to read a tanker engine’s name

A designation like 7G80ME-C9.5 is a bit of a mouthful. It’s also the most useful line on the nameplate.

WinGD uses a similar logic: an X72DF has a 72 cm bore and runs on dual fuel.

Tanker engine size by tanker class

The tanker class sets the engine size. Here are real examples, from product tankers to the largest crude carriers.

Deadweight ranges follow the commonly used AFRA and flexible market scales. Power figures are for the named ships or engines. Your ship’s figure depends on its design, derating and any power limit.

SMCR stands for “specified maximum continuous rating”, which is a fancy way of saying the power the engine was set up to deliver on this particular ship. The same engine model can be rated quite differently on two ships.

So how big is an oil tanker engine?

In horsepower, a VLCC engine of around 22,500 kW is roughly 30,000 hp. The largest tanker engines, like the ULCC example above, pass 50,000 hp. Physically, a two-stroke main engine rises through several decks, and the engine room is designed around it.

The largest ship ever built, the 564,763 dwt Seawise Giant (1979–2009), didn’t have a diesel at all. It used two boilers and a steam turbine rated at 50,000 hp (Wikipedia). Steam lost to diesel on fuel consumption. If your fleet includes older tonnage, though, you’ll still meet the generation in between: Sulzer RTA and MAN B&W MC engines, which are still running and still need parts.

What else runs in a tanker engine room?

The main engine gets the attention, but it’s only one of several engines on board. Here’s the rest of a typical tanker engine room.

Auxiliary engines (gensets). Medium-speed four-stroke engines make the ship’s electricity, and most tankers carry three or more sets. The usual names are Hyundai HiMSEN, Daihatsu, Yanmar and Everllence or Wärtsilä four-strokes. The designation logic is similar: a HiMSEN 6H21/32 has six cylinders, a 21 cm bore and a 32 cm stroke.

Boilers and cargo pumps. This is where tankers differ from bulk carriers.

• Crude carriers usually discharge with large cargo pumps in a pump room, driven by steam turbines. The ship’s boilers supply the steam, and also heat the cargo and fuel.
• Product and chemical tankers usually have a deepwell pump in each cargo tank. These are driven electrically or hydraulically, with no pump room (Marine Insight).

Everything else: the inert gas plant, fuel and lube oil purifiers, fresh water generator, compressors and an emergency generator.

What slow steaming and EEXI mean for the engine

Since 2023, existing ships have had to meet IMO’s EEXI efficiency requirement. Many tankers comply with an engine power limitation (EPL) or shaft power limitation (ShaPoLi). EPL limits the maximum amount of fuel injected per stroke, and it has to be documented in an approved onboard manual (DNV, 2025).

Here’s what that means in practice: engines spend more hours at low load. Low-load running tends to foul turbochargers and exhaust gas boilers faster, and it changes how the cylinders wear. The makers publish low-load guidance. Follow it, and watch the parts it names.

Fuel is the other reason speed stays low. Published estimates put a VLCC at roughly 60–100 tonnes of fuel a day, a Suezmax at 45–60 and an MR tanker at 25–40 (Maritime Page, 2026). Let’s be careful with these, though. They depend on speed, weather, hull condition and whether the ship is laden or in ballast. Here’s what they mean in practice: for a VLCC, saving five tonnes a day over 300 days at sea is 1,500 tonnes of fuel a year.

Dual-fuel tanker engines

New fuels are arriving in the tanker fleet too. In 2021, ten 300,000 dwt VLCCs were ordered with 7G80ME-GI engines that burn LNG or fuel oil, for charter to Shell (MarineLink). WinGD’s X-DF engines went into LNG-fuelled Aframaxes from 2018, and methanol-capable engines followed for Suezmaxes and VLCCs.

For purchasing, this matters because a dual-fuel engine adds a whole gas or methanol system, with its own valves, seals and sensors. Those are new part numbers, with shorter supply histories.

What wears out on a tanker main engine?

A two-stroke main engine is built for very long service, but the same parts keep coming back on the repair list. The figures below come from Everllence (then MAN) service experience published in 2008 (Riviera). They show the scale involved. They aren’t your ship’s intervals.

That’s the theory. At sea, fuel quality, cylinder oil feed rate, hours at low load and the last overhaul all change the picture. Your intervals come from the maker’s current instruction manual and service letters, plus the measurements your engineers take at each overhaul.

Imagine the scene. A VLCC is due to load in four days. At the last scavenge port inspection, the second engineer found broken rings on unit 4. The spare ring set is on the inventory list but not on the shelf, and the quote in the inbox says three weeks. So who decides: the chief engineer, the superintendent or the purchaser? In practice, whoever is under the most time pressure. Every option that follows costs more than the ring set would have cost sitting in the store.

Which tanker engine spares to keep, and how to order them

Start with the maker’s recommended spares list and the class requirements. On top of that, well-run tanker engine rooms usually keep:

• A complete exhaust valve, or at least a spindle and seat. Lead times can be long, and a leaking valve affects the whole unit.
• Fuel valve nozzles and overhaul kits. They’re used constantly.
• Piston rings and a full set of gaskets and O-rings for a unit overhaul. A unit opened without them stays open.
• Bearing shells for the most critical positions, where lead times justify it.
• Genset spares: fuel injection pumps and valves, plus cylinder head gaskets for the auxiliary engines.
• Turbocharger spares, as covered in our turbocharger guide.

To get the right part the first time, send:

1. Engine designation and mark (for example 7G80ME-C9.5), plus the engine builder and serial number. A photo of the nameplate is ideal.
2. Part numbers and plate or item numbers from the maker’s spare parts catalogue.
3. Main engine or genset, and for a genset, its own maker, model and serial number.
4. The documentation you need for class, PSC or company records.
5. Port and ETA.

The engine builder matters because the same design is built by different licensees. The mark matters because it can change the part even when the name stays the same. Ordering from a photo of the old part alone is… optimistic. Here’s why the wrong part number can cost you more than the part itself.

The main message

A tanker engine isn’t one engine. It’s a slow two-stroke main engine plus its turbocharger, gensets, boilers and cargo pumps, and each has its own makers, marks and part numbers. Know the designation, keep the slow-to-get parts on board, and order against the serial number, not the photo.

Need spares for Everllence/MAN B&W, WinGD/Wärtsilä or Sulzer tanker engines, or for the gensets beside them? Send the part number and a nameplate photo. We’ll confirm today. Engine spare parts → · Send a request →