QX60 3.5L (JATCO CVT8)

COMMON PROBLEMS: shudder or judder under light steady throttle, RPM flare without acceleration, scorched-smelling fluid, metallic sparkle in the fluid, delayed engagement

We lead with the QX60 because heat is what ends this transmission, and its temperature data tells us more than any single symptom. Crawling traffic and long grades push the NS-3 fluid past its limit, the steel push-belt and the pulley faces glaze, and the metal shed from that wear travels into the valve body and upsets pressure control. We hook up a scan tool and watch CVT fluid-temperature and slip data on a road test, because a judder under light steady throttle behaves one way and a flare where engine speed climbs while the car hangs back behaves another. A drawn fluid sample adds its own evidence, since a scorched smell and a metallic glitter mean the friction surfaces are already shedding. The numbers and the sample together decide between a fluid service paired with a valve-body repair and a full replacement unit.

G35 AND G37 3.5L/3.7L (VQ35/VQ37)

COMMON PROBLEMS: rising oil use between changes, blue smoke on cold start, cold-start timing chain rattle, oil in the spark plug wells, fouled plugs

A VQ35 or VQ37 in the G35 and G37 can shed oil along two separate paths, and our first job is telling them apart. Overnight, hardened valve-stem seals weep oil down the guides, and you see the result as that blue cloud at the first cold start; under load, coked oil-control rings let combustion gas drive oil up into the crankcase. We log a documented oil-consumption check across a measured interval, then thread a borescope through the plug holes to read the cylinder walls and piston crowns for carbon. A leak-down test settles the argument, because air hissing from the dipstick tube means the rings have given up while air at the tailpipe points to the valves. Owners also describe a one-second rattle at startup, which traces to a chain tensioner that bled down overnight, so we confirm oil pressure and inspect that tensioner before the chain ever takes the blame.

Q50 AND Q60 3.0L TWIN-TURBO (VR30DDTT)

COMMON PROBLEMS: oil pooling in the charge piping, blue smoke under boost, oil-use complaints, fouled downstream sensors, a change in spool or a whistle

The VR30DDTT spins two turbochargers, and a worn thrust or journal bearing lets oil slip past the shaft seals into the compressor and turbine housings. Pull the charge pipes, and pooled oil at the low points names the path, because an oily film on the cold side puts the compressor-side seal under suspicion. We feel the shaft by hand for the axial play that signals a failing bearing, and we scope the downstream sensors for the oil fouling that lights driveability codes. Under boost that same oil burns in the chambers and shows as smoke, so the visible smoke and the measured shaft play have to agree before we condemn a cartridge. Tying the leak to its path this way protects a healthy turbo when the real culprit turns out to be a PCV fault or a leaking valve cover.

QX80 5.6L V8 (VK56VD)

COMMON PROBLEMS: rough cold idle, misfire codes, hesitation under light throttle, steering-wheel shimmy under braking, brake pulsation through the pedal

Direct injection gives the VK56VD its efficiency, and it also bakes PCV oil vapor onto the backs of the intake valves where no fuel spray washes them clean. That carbon chokes airflow and ruins the valve seal as it grows, surfacing as a rough cold idle and misfires that cluster on the dirtiest cylinders. We send a borescope down the intake runners to grade the deposits with our own eyes, and a heavy grade earns a walnut-blast that returns the valves to bare metal. Braking shimmy is a second, unrelated measurement on a truck this heavy, since its rotors can wander out of true over the miles. We seat a dial indicator against the rotor face, read runout against the factory threshold, and let that number decide whether we machine the rotor or replace it.

FX AND QX70 COOLING AND HEAD GASKETS (S50/S51)

COMMON PROBLEMS: temperature gauge climbing under load, coolant loss with no visible puddle, bubbling in the overflow tank, white exhaust vapor, a sweet smell after a drive

An early FX can run hot once its cooling system loses the margin it was built with, and an engine that overheats long enough can stress a head gasket. We open with a combustion-gas test on the coolant, pulling vapor from the radiator neck through a chemical block that shifts color the moment exhaust gas reaches the coolant. A pressure test follows, and a system that bleeds down under a held pressure points us toward an internal loss. When bubbling in the overflow under load lines up with that color change, combustion gas is pushing into the water jacket, which reads differently from a seeping radiator seam or a water-pump seal that drips while the engine turns. Reading the system this way keeps a tired hose clamp from being charged as a head gasket.

LIFTGATE WIRING ACROSS THE SUVS (QX60/QX70/QX80/FX)

COMMON PROBLEMS: intermittent backup-camera dropout, rear wiper that quits, liftgate lock or release acting up, flickering rear defrost, faults that come and go with the door

Open and close the rear hatch enough times and the wiring inside its hinge boot pays the price, flexing on every cycle until a conductor fatigues and cracks inside its own insulation. From the outside the wire looks whole while the copper underneath has split, and the fault blinks in and out as the broken strands brush together and pull apart. We run a flex-and-wiggle continuity test right at the boot, working the bundle by hand while we watch the circuit drop, which lands the break within an inch of where it lives. Then we repair the fractured strands, because the camera and the wiper are doing their jobs while a hidden wire takes them down. A module gets blamed for this fault all the time, and the continuity reading is what aims the repair at the conductor that failed.

DRIVE IT IN

We separate a worn joint from a cooked transmission with the test the symptom calls for, so the fault you pay to fix is the fault we measured. Is your Infiniti smoking, or flashing a code that refuses to stay put? Call Driven Auto Care of San Ramon at (925) 830-4701, and the first thing we reach for is an instrument. Bring us the symptom, and we’ll bring you the cause.