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Thanks to YNOT for the detailed response on why people call some 3lt diesel motors "Grenades".
There are heaps of threads on other forums on the subject (sounds like you found some of them), but the early ZD30 engines fitted to GU series 2 had reliabillity issues and developed a reputation as a grenade that could go off with out warning at any time. Series 3 onwards are more reliable, but it still pays to take a few precautions to make sure they stay reliable.
Most engine failures seemed to be caused by fouling of the Mass Air Flow (MAF) sensor with crank case ventilation vapours, causing the sensor to send incorrect air flow data to the engine computer. This results usually in over fueling, raising Exhaust Gas Temperatures (EGT's) to dangerous levels, which melts pistons and damages other engine components. Air flow into the cylinders can also be reduced (by Exhaust Gas Recirculation (EGR) carbon combining with the PCV oil vapours building up in the inlet manifold. Reducing air flow to the cylinders makes the over fueling situation worse.
There is a series of modifications (engine saver mods) that can be done to eliminate the causes of these faults.
As Nisspat said, it's usually the 4.2 owners that call them grenades.
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