On these VQ35s the plastic valve covers and the oil cooler O-ring fail as a cluster — oil in the plug tubes up top, a seep at the lower rear underneath. We fix the whole cluster in one visit at your home.
The VQ35 in the G35, G37 and FX35 uses plastic valve covers with the spark plug tube seals moulded in — not serviceable on their own. After a decade-plus of heat cycles the plastic hardens, the tube seals give up, and oil migrates down into the spark plug tubes. Oil around the plugs and coil boots is a slow poison: the boots degrade electrically, the spark weakens, and the engine starts misfiring — usually intermittently at first, which makes it maddening to chase.
At the same age, the O-ring sealing the engine oil cooler at the lower rear of the block dries out and starts weeping. It's a classic can't-find-it leak: the oil traces back along the block and crossmember, so the drip never appears where the leak actually is. Together these two failures produce the symptom cluster these cars are known for — oil smell, mystery seep, fouled plugs, intermittent misfires.
These two repairs belong together because the diagnosis and access overlap, and because fixing one while ignoring the other means the oil smell and the top-ups continue and you wonder if the repair worked. Left alone, the misfires harden into a constant stumble, oil-soaked coils fail outright, and unburned fuel from misfires shortens the catalytic converters' life — the expensive domino at the end of this chain.
If your Infiniti is doing any of these, this is the likely cause:
Oil in the plug tubes kills coils and fouls plugs on a schedule — the misfires you barely notice today become the stumble you can't ignore in a few months, and every misfire feeds raw fuel to the cats. The cooler O-ring is gentler but relentless: it seeps a little more each month, coats the underside, and keeps your oil level on a slow leak. Neither fixes itself, and both get more expensive in collateral parts the longer they run.
Yes — the valve covers are done from the top, the oil cooler from below with the car safely raised on a flat surface. It's a day's work at your home, and bundling them into one visit is the whole point: one setup, both leaks fixed.
Because the tube seals can't be bought separately — you're buying complete valve cover assemblies — and the combined labour for covers plus cooler adds up to many book hours at dealer rates. We price the complete bundle as one flat quote before any work starts, so you know the full number up front.
We pull a coil and look — oil in the tube is unmistakable. If the boots and plugs are oil-fouled, they get replaced as part of the job, but the covers are the root cause. Replacing coils without fixing the covers means buying coils again next year.
You can, but if the lower-rear seep is active you'll still smell oil and still top up, and you'll wonder whether the cover job worked. The cooler O-ring is a modest add-on while we're already there — splitting it into a second visit later costs more than bundling it now.
Send it over for a free second opinion. I'll tell you straight what the job actually involves — and if their quote is fair, I'll tell you that too.
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