We rebuild Patrol engines every week in Burleigh Heads, and the first thing we tell most customers is which engine they've got decides everything. A TD42 is worth rebuilding almost every time. A ZD30 is worth rebuilding sometimes. An RD28 is usually worth replacing with something else. Here's how we make that call.

How you know it's time

The signs are the same across engines; the cause isn't.

Oil consumption of more than a litre every thousand kilometres with no external leak means rings, valve stem seals or a glazed bore. Blue smoke on start-up that clears is stem seals; blue smoke under load is rings. White smoke that smells sweet is coolant, and that's a head or a head gasket. Blow-by at the breather hose with the engine idling, or a dipstick that pushes itself out, is rings or a cracked piston. A knock that changes with load is a big end; a knock that changes with revs but not load is usually a small end or piston.

Before we quote a rebuild we do a compression test and a leak-down test. Twenty minutes, and it tells us whether it's a top-end job, a full rebuild, or whether the engine is worth saving at all.

TD42 and TD42T

The 4.2 is the most rebuildable engine Nissan ever put in a Patrol, which is why we build conversion kits around it. Common reasons it ends up on our bench:

The naturally aspirated TD42 that has been turbocharged without the head being done. The factory NA head and gasket don't love 15 psi, and the result is a lifted head or a cracked head between the valves. The fix in the rebuild is a TD42T head gasket, ARP head studs instead of bolts, and the head pressure-tested and machined.

High-kilometre bores. A TD42 at 400,000 km is often still fine on compression but burning oil. We bore and hone, fit new pistons and rings, and it goes again for another 300,000.

Injector pump and injectors get done at the same time. Rebuilding the engine and bolting the old 400,000 km pump back on is false economy; on the turbo engines we usually recommend the 12 mm pump upgrade while it's apart.

A TD42 rebuild from us is the block, crank and head machined and measured, new pistons, rings, bearings, all seals, a new oil pump, timing gears checked (they're gear-driven, no belt), new water pump and thermostat, and the head done properly. It comes back with a 12-month warranty.

ZD30 DI and CRD

The 3.0 litre has a reputation for grenading, and most of the engines we open had the same story: overboost or overfuel, piston number three or four cracked at the crown, or a ring land let go. The root cause is almost never the engine itself. It's the intake, MAF and boost control on the DI, and a tired injector or a blocked EGR on the CRD.

A ZD30 rebuild is worth doing when the block and crank are undamaged and the owner wants to keep the vehicle original. We fit new pistons (all four, never one), rings, bearings and seals, test the injectors, and, this is the important bit, fit boost control and a catch can before it leaves, because without those it'll do it again.

If the crank is damaged or the block is cracked, a rebuild usually costs more than a TD42 conversion and gives you back the same engine. That's when we talk about a conversion instead; see Liam's GU S4 build for what that looks like.

RD28 and RD28T

The 2.8 cracks its head between the valve seats when it's overheated, and by now most have been overheated once. A head is possible, but a good second-hand RD28 head is scarce and a new one costs more than the engine is worth. Our honest advice for most RD28 owners is to put the money into a TD42 conversion. The RD28 Patrol is a good chassis with the wrong engine.

TB42, TB45 and TB48

The petrol sixes are tough. The TB45 and TB48 mostly come in for valve seals, timing chain guides and, on the TB48, head gaskets after running hot. They rebuild well and parts are still available. If you're considering an LS conversion on a petrol Patrol, we make the plug-and-play LS loom and can do the whole job.

Rebuild or convert

Rebuild when the block and crank are good, parts are available, and you want to keep the vehicle as it is. Convert when the engine is an RD28, a badly damaged ZD30, or when you want more than the factory engine will ever give you. A TD42T conversion into a GU costs more up front than a ZD30 rebuild, but it's the last engine that Patrol will need.

Either way it starts with a compression and leak-down test in Burleigh Heads. Call 07 3924 3317 or book online and we'll tell you straight which way to go.