reconditioned deisel engine for boat

Boat Engine Cooling Systems

Boat Engine Cooling Systems

Wes has recently been working on his favourite engine – a Volvo Penta.

There are two aspects to marine boat engines.

  • The Manifolds
  • The Cooling System

Listen to Wes talk

Keeping a Boat Engine Cool

The mainifold and the engine’s cooling system keep the engine cool and operating at optimum temperature. This is particularly important with a deisel engine.

Volvo Penta Engine Cooling Systems

The cooling system on a Volvo Penta for example uses both fresh water and sea water.

In a car, air cools the coolant which circulates through the engine. But for a boat engine we don’t have air, we have water.

Two liquids run through the heat exchanger, neither coming in contact with each other.

  • Sea water
  • Coolant (fresh water)

We take seawater from under the boat and pump it through a heat exchanger. The heat exchanger also has coolant (mixed with fresh water) running through it. The sea water cools the cooling water (coolant) throughout the engine via tubestacks.

tubestacks boat engine

Tubestack for a deisel marine engine

What’s a Tubestack?

This is done with “tubestacks” – a bundle of tubes. The coolant flows around the outside, while the seawater runs through the middle of the tubes. Or vice versa.

Older Marine Engines

Some of the older engines pump seawater around the engine to cool it. This would be best with stainless steel, but older Mercruisers (petrol engines) have cast-iron manifolds. Naturally they have a limited life – sea water being a corrosive solution. There are products on the market these days which neutralize the effect of the salt. If you use these products and flush your system out with fresh water on a regular basis, they can last up to 10, 12 years.

What about Outboard Engines?

Outboards also use sea water which is pumped around the block, but these are light, aluminium components. The water flushes through the system, unlike with an inboard motor where the water sits for long periods inside the engine.

The marine environment is a harsh environment for boat engines. You are always going to get some level of corrosion.

4 thoughts on “Boat Engine Cooling Systems

  1. Callum Palmer

    I’m looking at buying a boat here soon. I don’t know what type of engine it will have but I’d be sure to have it looked at before buying. That way I can be sure that all of the components, such as the cooling system, are working properly.

    1. Edwin Post author

      It’s certainly worth getting a boat checked out before you buy. Check with your local marine mechanic there in Sydney. We’re in Perth.


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