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The only place for a coil spring is up Zebedee's arse
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Makes sense but it doesn't explain why improving the lubriction to the oil control rings so they no longer stick in their grooves, without any other changes, particularly to the cats, prevents the problem. Or at least it does on the Toyota engine that suffered the same problem.

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The only thing I could see that might be making the difference is if it meant the oil control rings were doing their job better, thereby not sending excess oil down the exhaust where it can contaminate the lambda sensor, honeycomb of the cat (possibly also causing it to become sticky and attaching further debris) and thereby causing eventual failure of the cat. Oil isn't generally wanted to go down the exhaust system in cat equipped vehicles for both of the reasons above. Trouble is by the time its failed in the manner described, it might be hard to see what started the process by the amount of damage done.

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It's probably the first time I've heard of the Toyota problem so I don't know the conditions Toyota owners have had ruined engines under, I don't have enough info to draw comparisons etc.

Can say that with the Elgrands all owners seem to only use the recommended fully synthetic oil, Nissan did a 'fuelling' recall on them during which they checked condition of catalytic convertors (Nissan are aware cats fail and when cats fail it can bugger the engine but they blamed it on over-fuelling), it doesn't seem to make a difference if the engine was a clean runner right up to the point of failing or burned a bit of oil for years before failing.

I can see what differences the fuelling recall made to fuelling when I'm calibrating LPG systems (can compare pinj between those that have had the recall done and those that haven't), they did lean off the top end a bit and prevent a very lean mixture still being injected on over-run in the recall but the recall seems to have done nothing to prevent failures. For running on LPG it doesn't really matter if the recall has been done or not, mixture on LPG can be the same, just a matter of setting multiplier at the high load end correctly and filtering short pulses on over-run.

I'm not saying oil starvation hasn't wrecked a few engines but nobody has yet suffered the same type of engine failure when cats have been removed.