ZD30 Patrol: Your guide to the Nissan Patrol ZD30 engine
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It’s often said that you have to challenge perceptions and traditions in order to achieve progress. So when Nissan moved, in 2000, to fit its successful Patrol franchise with an engine other than an inline six, Patrol enthusiasts everywhere were all ears.
Optional on the Patrol station-wagons as well as the tradie/farmer-oriented cab-chassis line-up, the ZD30 was not just a four-cylinder engine, but a much more modern take on the turbo-diesel engine theme, complete with technology such as balance shafts, double overhead camshafts and even four valves per cylinder. It should have represented a definite step forward in terms of efficiency and fuel economy but, in the end, the ZD30 was remembered neither for those attributes nor remotely fondly.
On paper, it delivered more or less what people were expecting of the 2953cc unit. Power was a claimed 116kW at 3600rpm with beefy torque of 345Nm at 2000rpm. You could choose either a five-speed manual or four-speed automatic transmission and the latter was particularly good in off-road conditions such as sand and mud. But even with those numbers, you need to remember that the engine, as fitted to a Patrol wagon, was tugging along a 2.3-tonne payload and that was before you filled the 125-litre fuel tank and added people, luggage and a bulbar and winch.
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Nevertheless, those power and torque figures were actually a handful more than the old faithful 4.2-litre turbo-diesel six-cylinder that sold alongside the ZD30-powered Patrol (the four-cylinder was several thousand dollars cheaper depending on specification) so it was clearly tuned reasonably aggressively. And perhaps that was part of the problem.
Long before they should have been starting to blow up, the ZD30 was confronting owners with catastrophic engine failure. The bulk of the failures tended to involve either number three or four piston with either a hole in the piston crown or a crack through the top ring land. Either way, it was a huge fix and amounted to a complete bottom end rebuild.
Typically, the Nissan fixit industry reacted quickly and pretty soon, a handful of potential causes were being proposed. The first of those was that the action of the exhaust gas recirculation (EGR) valve was playing merry hell with the fuel-air mixtures within the individual cylinders. In extreme cases, the mixture in a cylinder could be so slewed that hot spots occurred on the piston and in the combustion chamber. If the temperature got high enough for long enough, those hot spots could cause the piston failure that characterised the bulk of ZD30 engine failures.
The second cause thrown up was that the Mass Air Flow (MAF) sensor was becoming contaminated with oil in the inlet tract due to the process of the crankcase ventilation system. By venting the crankcase into the inlet manifold (where the gases go through the engine and are brunt) there was always the possibility that oil fumes from those crankcase gases could contaminate the MAF sensor. If that happened, the MAF sensor (which is responsible for telling the on-board computer how much air is going into the engine so the ECU can tailor the fuel supply to the injectors to match) could send an erroneous signal to the computer with an incorrect fuel-air mixture as a result. Once again, that could increase the combustion chamber temperatures beyond the safe zone. And there goes another piston.
The other problem suffered by the ZD30 was down to the actual engine’s slow responses to commands from the computer. Typically, that manifested in damaging boost spikes where the computer detected an overboost situation, but the engine hardware was too slow to over-ride the situation. The result of that was the potential for a series of damaging boost surges that have also been credited with grenading pistons.
But it seems the ZD30’s problems were even a bit more fundamental than that. Somehow, Nissan managed to specify an incorrect oil volume in the engine’s specifications, listing six litres as the oil capacity of the engine. But questions began to be asked when owners started experiencing oil starvation even though the oil level was not critically low on the dipstick. Much head scratching led Nissan to change its mind and alter the published oil capacity to 8.3 litres (a huge difference - 38 per cent more!) and instructed dealers to shorten and recalibrate dipsticks.
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Up to 2006, the ZD30 used a conventional fuel-pump system to distribute the fuel to each cylinder. But at that point, the engine switched over to common-rail injection which, depending on who you talk to, helped with some of the engine management issues that had been causing boost spikes and incorrect fuel-air mixtures.
But by then, the damage was done to the engine’s reputation. That didn’t stop Nissan continuing to use the unit, though, and in fact, it survived right up until the end of Y61 production in 2016. It was also the only engine to be fitted to the Patrol by then, but in reality, those very last Y61s were only marketed to appease the hard-core diesel fans who couldn’t cope with the petrol-only Y62 that had launched in 2013.
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