7 Key Points To Marine Diesel Turbo Longevity

Understanding Turbochargers

To benefit from our 7 key points to marine diesel turbo longevity, we first need a basic understanding of what a turbocharger is, and what purpose it serves.

Induction and forced induction

Our marine diesel engines draw air into each cylinder by movement of the piston. The stroke of the piston in the bore ‘swept volume’ determines the amount of air each piston can ‘induct’ into the cylinder. Swept volume is the same for each cylinder, meaning power output remains the same. By physically forcing more air into each cylinder we can alter the compression ratio, resulting in increased power output.

With more air, means more fuel, more fuel means more power. Why do we want more power? Well, you don’t often hear people complain of having too much engine power.

The exhaust side of the turbo (orange) drives the air side (blue)

How does a turbocharger work?

Turbochargers work by utilising the engines exhaust gases. You might be thinking, how? Exhaust gases leave each cylinder and travel through the exhaust manifold into the turbocharger, spinning a turbine. This exhaust turbine is attached by shaft to another turbine on the inlet side, which is called the compressor turbine, and as the two turbines spin, air is sucked in and compressed in the inlet manifold, ready for each cylinders combustion process.

What about superchargers?

Superchargers work on the same principle of forcing air into the engine. They are powered/driven not by exhaust gases but by mechanical means to the engine, whether it be by belt, chain or gear. Superchargers are initially more responsive than turbochargers and provide excellent low down torque.

Issues that arise from forcing or compressing air into an engine

As air is compressed into an engine, it gets hot, and the hot air expands and as a result, less air can be compressed into a cylinder. As inlet air gets hot its efficiency to combust also lessens. Due to this process, an additional cooler is required to be fitted to the engine to cool the compressed air – this is often referred to as the aftercooler/intercooler/charge air cooler.

Types of turbochargers

Variations of turbos can include dry turbos with heat shielding, jacketed turbos with coolant passages to help cool the exhaust side of the turbo.

Another type of turbocharger is a VGT, which stands for variable geometry turbo. These turbos have veins which can actuate to increase and decrease the efficiency/RPM of the turbo. One of the biggest benefits of VGTs is that one turbo can be fitted to be effective over a larger RPM range of the engine. 

Methods of forced induction

  • Single turbocharger – with this simple design, all exhaust gases are routed through the exhaust side of a single turbo and all air on the inlet side is compressed by one turbo charger then routed to the engine (often via a charge air cooler first).
  • Super charger and turbocharger – the supercharger handles the initial load, an electromagnetic clutch engages and disengages at a particular set RPM and/or engine load. During this initial supercharged induction the volume of exhaust gases increase and allows the turbocharger to spool up before excessive load is applied, creating a smooth power curve.
  • Multiple turbochargers – these are either parallel or compounding/sequential. Parallel is where two or more turbos supply the same inlet manifold. Compounding/sequential is where you have one turbo supply air to another turbo (for example, in replacement to a supercharger a small turbo spools up quicker than a larger turbo) so exhaust is directed into the small turbo first, then once a particular inlet and exhaust manifold pressure is achieved the exhaust gases diverts to the larger turbo to continue the forced induction.
MAN marine diesel with quad turbochargers

7 Key Points to Marine Diesel Turbo Longevity 

Now that you have a basic understanding of how a turbo works, here are our seven tips for turbo longevity.

1. Oil cleanliness

It’s important that you stay on top of your hours based or at least annual servicing. This includes replace oils, filters and use the manufacturers recommended grade of oil.

2. Allow your engine to warm up

Try not to load your engine until you’ve reached your operating temperature. This comes down to lubrication and oil viscosity as well as temperature indifferences between your engines components. 

3. Allow your engine to cool down

When returning to berth or anchoring, give time for your engines to idle, and cool down. Your turbocharger needs time to spool down, as the shaft within your turbo can spin at speeds of up to 300,000 RPM. Once you stop the engine, oil pressure ceases and so does the lubrication to the turbo shaft bearings.

4. Allow your turbo to spool up

Open up the RPM and feel comfortable. Extended idling, trolling, low speed cruising can cause the exhaust turbine to soot up, lessening efficiency hence decreasing optimal combustion and power. The saying “use it or loose it” rings true here.

5. Complete your saltwater service on time

Overhaul aftercoolers/charge air coolers periodically, prior to failure. With turbocharged/aftercooled engines it is imperative to have your coolers overhauled (removed, disassembled, inspected, resealed, pressure tested and refit). Most aftercoolers that are on the market are saltwater cooled. Saltwater crossing into your boost air, inlet manifold and combustion process can be fatal to an engine. Best not to allow this to happen!

6. Inspect your exhaust mixers regularly

Exhaust mixers do just that, mix saltwater with the engines exhaust gases to cool and dispose overboard. Exhaust mixers can internally fail with saltwater reverting into the exhaust side of our turbocharger, exhaust manifold and the cylinder heads exhaust valves. By removing and internally inspecting the exhaust mixer (also allows a look at the exhaust turbine). This can prevent potentially significant engine damage occurring, and will significantly help with your turbo longevity.

7. Keep your air filters clean

If air can’t get in, then air can’t get out! It’s imperative that you clean or replace air filters along with your engines servicing schedule. Air filters act as guard to protect the engine from sucking in any foreign material. These foreign materials could be objects such as rags left in the engine room, degrading engine room insulation, or even your mechanic’s shirt! If you have a paper style filter fitted, you’ll need to ensure that it remains dry, and to replace it if it becomes wet. Trust me on this one, you don’t want a wet air filter sucked into your engine.

Ultimately, turbochargers are a vital and expensive part of your diesel engine. By providing adequate care, you can increase the lifespan and efficiency of your marine diesel engine.We hope these seven tips help increase your turbo longevity!

Glossary 

Charge Air Cooler/Aftercooler/Intercooler: Charge air coolers (otherwise known as intercoolers/aftercoolers) act as the middleman between the turbo and the engine. They take the hot, compressed air from the turbo and cool it down before it reaches the engine.

Exhaust Mixer: The exhaust mixing elbow takes the cooling saltwater and mixes it with the exhaust gases from the exhaust manifold. Also known as the exhaust elbow.

Exhaust Elbow: The exhaust elbow takes the cooling saltwater and mixes it with the exhaust gases from the exhaust manifold. Also known as the exhaust mixer.

About the Author – Brendan Sutton

Brendan is a dual certified Marine Surveyor & Engineer, who completed his trade at well respected marine engineering company based on the Hawkesbury River. After relocating his family to the Gold Coast, he joined the BoatBuy team in QLD. Liked this article? We would love to hear from you. Feel free to email Brendan with any boating related questions you might have here.

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