Review: Yanmar 6LPA-STP2 marine engine
Under the guise of the Yanmar 6LPA-STP2 marine engine, a Toyota LandCruiser 100 diesel lives on in a Cresta 32 gameboat.
Some of us just love simplicity and don’t want newfangled things like electronic engine management. My two cars have carbies because they’re way simpler to fix than fuel injection.
My mate Chris is one of these people. With his trucking background and having owned a LandCruiser 100 he wanted the same repower engines in his 1980 Cresta 32 gameboat. Out with the old 440 cu in (7.2lt) 330hp Chrysler V8s and in with 4.2lt diesels that actually develop more torque.
The Yanmar 6LPA-STP2 (surely there’s a simpler way of designating engine models) is the same base engine as the 100 unit but has mechanical fuel injection.
YANMAR 6LPA-STP2 MARINE ENGINE
No getting away from boring tech bits when I review an engine! This straight-six marine motor with wastegated turbocharger and charge-air intercooler displaces 4164cc with a bore of 94mm and stroke of 100mm to provide effective combustion chamber "squish". The 24 valves are operated by a single belt-driven overhead camshaft. Like European engine manufacturers, Yanmar loves quoting output in metric horsepower (mhp), but I’m old school where 1hp = 746 Watts, so the output is 311bhp (brake horsepower) at 3800rpm, with a maximum continuous output of 283bhp at 3600rpm.
The Yanmar 6LPA-STP2 engine has a pleasure-craft rating with typical operating hours per year of 250 and maximum output of less than five per cent of the total or no more than 30 minutes at a time. That’s plenty for recreational usage.
What really impresses me is the torque figure because, as we all know, plenty of torque at relatively low rpm gets a hull out of the hole quickly without labouring the engine and this one pumps out 700Nm from 2200 to 2400rpm with 580Nm available at 3800rpm. Torque rises quickly from 400Nm at 1600rpm and as Chris’s Cresta planes at 2200rpm and cruises at 2500rpm, the torque output is perfectly matched to the hull.
The voltage regulated alternator on the Yanmar 6LPA-STP2 puts out a maximum of 80amp and in this hull a close-coupled V-drive box with 12-degree down-angle output shaft keeps the engines in the cockpit where they’re easily serviced. Chris’s gearboxes have a 2:1 reduction driving cupped four-bladed 19 x 21in props.
Yanmar recommends using SAE10W30 or 15W40 sump oil but Chris uses straight 30 monograde oil, because not having any viscosity index improvers it’s less likely to breakdown under high loads. Chris changes the sump oil and filter annually and the camshaft timing belt should be checked annually for fraying and replaced every 800 to 1000 running hours.
Complete with the standard eight-degree down-angle hydraulic gearbox, the 100 engine is 1257mm long by 700mm wide by 812mm high and has a dry weight of 451kg. The V-drive box adds just 1kg to this weight.
PERFORMANCE ON THE WATER
Starting this direct injection engine is straightforward: wait for the glow plugs to preheat the combustion chambers and turn the key. When the engines have been left unused for a while, there’s the usual grey exhaust smoke from condensation but black smoke appears only when the hull is coming out of the hole with the engines well loaded. The Cresta is well balanced fore and aft and doesn’t need trim tabs to plane or at any other time.
When idling, there’s the usual diesel rumble but not enough to be annoying and being mounted under the cockpit sole they’re relatively quiet despite no soundproofing being fitted. With the engines idling, the one ahead/one astern spins the boat quickly. The cockpit drains are well above the static waterline, so when backing into a slop if any water does come aboard and gets under the lazarette hatch, due to a full-width bulkhead here it won’t reach the engine compartment.
The Cresta gameboat is no slouch coming out of the hole but accelerates quickly once planing right out to maximum rpm. Through tight turns, the engines maintain their set rpm and as the hull has a deep-vee it banks well over into the turn and being a yachtie, it’s something I never get used to. Sure, tinnies do the same but when you’re high up in a flybridge the effect seems all the more dramatic!
THE TRADE-A-BOAT VERDICT
The 100 engine is one of only three straight-six Yanmar motors left with mechanical injection as more recreational boaters want electronic and drive-by-wire controls. They also want fuel usage and range-to-empty readouts, something not so easy to set-up in mechanical engines.
But being an old fart with traditional ideas, I love the relative simplicity of the 100 engine that is the Yanmar 6LPA-STP2.
The only problem has been corrosion on one of the exhaust elbows, not bad for the pleasure the repower has given Chris and his family.
For more on this engine, contact Power Equipment at firstname.lastname@example.org
YANMAR 6LPA-STP2 SPECIFICATIONS
TYPE Straight-six turbo-diesel
MAX HP 311 at 3800rpm
BORE X STROKE 94mm x 100mm
COMBUSTION SYSTEM Direct injection
ASPIRATION Turbocharged with intercooler
DRY WEIGHT 408kg
More boat engine reviews
Originally published in Trade-a-Boat #444, September/October 2013.
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