Cox CXO 300hp tested: Is this diesel outboard the real deal?

What better way to test the production version of the Cox CXO 300hp than on the brilliant Axopar 37? Is this a new dawn for diesel-fuelled outboards?

British company Cox Powertrain’s first engine fired up more than ten years ago and set the UK-based company on its path to revolutionise the diesel outboard market.

We have followed the company’s progress keenly and, back in early 2019, editor Hugo was the first journalist in the world to test the CXO 300hp prototype fitted to a Tornado RIB on a lake.

Now, Cox’s production facility in Shoreham-by-Sea is fully up and running and, thanks to the vision of German Axopar dealer Patric Polch, we have the opportunity to test the engine on a boat that we know very well indeed, the Axopar 37.

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I have probably done more sea miles in an Axopar 37 than any other boat I have tested, and know the boat intimately, which would hopefully make comparisons with the petrol outboards that are usually fitted to this boat all the more pertinent.

Though I know the boat very well, this would be the first experience I’d ever had of not just the Cox but any diesel outboard, except for the odd crude commercial unit I’d come across on my travels.

The sheer size of the units is what most stands out upon seeing them in the flesh. The familiar Axopar Cross-Cabin shape is punctuated at its aft end by the somewhat less familiar cowlings of the 300hp, 4.4-litre V8 diesels.

Though they are large on the transom, with the lids off it’s clear what a brilliant job Cox has done with packaging these engines.

The motor – developed from scratch for this purpose – has a vertical driveshaft that connects to a 90-degree transfer case built to manage all that lovely torque produced by the twin turbos that are tucked neatly down each side of the engine.

It certainly fills the transom more than the usual V8 Mercury petrol would but it’s a nice-looking unit that suited the all-white Axopar test vessel down to the ground.

Read our full review of the Cox CXO 300hp diesel outboard in the September issue of MBY, which is out now


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