Marine Engine Review: Yanmar 6LY 440

The Yanmar’s 6LY3 diesel series now has electronically-controlled fuel injection that provides cleaner running and fuel control.

I first tested twin 440s in 2000 in a Fabio Buzzi 38 sports boat which had innovative two-speed ZF gearboxes and reached a top speed of 63kt. Despite the mechanical injection, black exhaust smoke appeared when going astern due to the load of the massive semi-surfacing props — once planing and running the second gear, no smoke appeared.

The next year I tested twin 440s in a Black Watch 36, which, due to its aft weight bias, needed down-angled trim tabs to reach 27kt. But again, black smoke appeared when going astern and coming onto the plane before load decreased when fully planning, and overall the 440 was remarkably clean running for a mechanically-injected engine.

The current 6LY3 series is available as a 400 and 440, both developing peak output at 3300rpm. However unlike the ETP maximum torque is down slightly to 1200NM but this is developed from 2100–2500rpm, which is way more useful for planing a hull. The ETP used is 95L/h at Wide Open Throttle, compared to 87 for the current 440, which has high pressure electronically-managed common rail fuel injection. Admittedly the decrease in fuel flow is proportional to the output reduction, but remember manufacturers fit CR more to meet ever toughening exhaust emission regulations than to improve engine torque and peak output. For example, the current 440 has US EPA Tier 3 compliance compared to Tier 2 for the three 6LY3 series engines. 

To provide more re-powering flexibility, the current 440 is also rated for light duty commercial operation (1000 running hours per year), whereas the three 6LY3 series engines had pleasure duty rating, or only 250 hours per year. Frankly that ain’t enough for boaters who actually use their boats instead of leaving them in a marina or on a mooring to slowly decompose.

Riviera now warrants selected models for 2800 hours over seven years or 400 hours of operation per year. Where would the pleasure duty rating fit into this equation? This rating might be okay for small yacht engines, but certainly not for cruisers. 

In the Details

The 6LY 440 might appear to be a high revving engine compared to some of the competition, but it’s still lower revving than the Toyota-based Yanmar 8LV 370, which in my opinion is an ideal engine for re-powering cruisers running big block petrol V8 engines. The fact that the 440 has a 30 per cent larger piston displacement but develops only 19 per cent more power shows that in comparison it’s under stressed. But then, as expected of a straight six compared to a V8, the peak torque output is 50 per cent higher — not bad considering that with hydraulic gear box the 440 is only 35 per cent heavier. It just shows that for most recreational cruisers under 15m, nothing compares to a straight six!

The 6LY 440 has high pressure electronically controlled Denso common rail fuel injection enabling it to meet the US EPA Tier 2 and European RCD (recreational craft directive) 2 exhaust emission requirements. Common rail is not as precise as the electronically controlled unit fuel injection fitted to more powerful Yanmars, but it’s a good compromise. And because the system is engineered by Denso, one of Japan’s finest electronics manufacturers, it should have a long, trouble free lifespan.

Back in the 2000s, Yanmar rated the 440’s output using diesel fuel density of 860 grams per litre, the Japanese and European standard, not US and Aus, which suffered 840 grams per litre. This meant that all Yanmars developed sold in Aus developed less power than their European and Japanese counterparts. Fortunately, Yanmar now rates the 440 and other engines to perform on diesel available, so the engine still develops its designed torque and power. Rating engines at 840 grams gives a more level playing field.

Standard is heat exchanger cooling with a sea water cooled inter cooler, allowing for a more compact engine than fresh water cooled inter cooling. The electrical system is 12V with a 125A regulated alternator fitted.

A welcome trend nowadays is that more gear box manufacturers are offering eight degree down angles at the output flange as standard. With the common prop shaft angle in planing hulls being around 12-degrees (apart from Maritimos), the engine needs only a four degree installation angle, reducing engine height at the forward end and all but eliminating the possibility of lubricating oil starvation when the hull is coming onto the plane. And with many sump drain plugs being midway along the sump, more old oil can be removed when changing the oil and filter(s).

Yanmar recommends using an SAE 10W30 sump oil in temperate climates and SAE 15W40 in tropical conditions. I suggest changing the oil and twin oil filters every 100 running hours or six months as the 440 is a fairly highly stressed engine.

The KMH6 1A2 hydraulic gearbox fitted to the 440 has an eight degree angle and is available with 1.55:1, 2.04:1, and 2.43:1 reduction ratios ahead and astern. Unfortunately, none of the deeper astern ratio of gear boxes are fitted to Yanmar’s yacht diesel range! For most planing-hulled cruisers the 2.04:1 ratio should suffice.

Complete with this box, the 440 is compact for its output, and measures 1440mm long, 749mm wide, and 774mm high

On the Water

I’ve only tested the 440 in mechanical form but I think the main benefits of owners of the electronically managed 440 would be slightly better throttle response, no black smoke under load, and the ability to see real time fuel flow via Yanmar’s VC10 instrumentation which includes the ‘drive by wire’ throttle and gear shift controls to eliminate the ‘clunk’ of cable controls.

In my opinion the 440 suits deep-V planing hulls in the 11–12m range in twin installations.

The Wrap

Thankfully Yanmar is a conservative engine manufacturer and puts a lot of effort into developing its engines. The 440 has been around for more than 20 years in one form or another, meaning spare parts are readily available. Combined with Australia-wide dealers and servicing agents owners should have no trouble keeping their engines running for countless years.

Sea Trials

As with any diesel the 6LY 440 should be slightly under propped to reach 3400rpm under normal hull loading. This will allow for slight hull and prop fouling between slipping. 

Note the flat torque curve right where a correctly-trimmed hull should plane, and that 79 per cent of maximum torque is still available at Wide Open Throttle. 

Specs

*Brake horsepower/metric horsepower or PS

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