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The Subarus are biggish unstressed engines so spend a lot of their time at low revs where they burn inefficiently, however the Suzuki is being thrashed just to get to the shops.
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E3,
I grew up reading that the inside of the exhaust should be a light grey (too white = lean, black = rich) on older 4* cars without catalytic convertors. My first cars all agreed with this and gave good economy.
All my subsequent cars with cats havent shown this behaviour, Holden barina (Corsa), Subaru Outback 2.5, Volvo V40 1.8 all running on unleaded with a Cat and good economy but with sooty exhausts (not oily though). Asked once for the mixture to be checked but all ok (all cars used mainly for long journeys).
Not really an explanation, but hope it is useful background
StarGazer
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One of the products of combustion of petrol (and other hydrocarbon fuels) is water. If the exhaust pipe is hot enough the water will come out as steam which, once the system has warmed up, you probably won't notice because it will be a small proportion of the total exhaust gases. If the water condenses just before the end of the tailpipe it will drip out of the end. I've had cars where this happened and the result was that the end of the tailpipe corroded and ended up looking quite ragged. On most cars the condensation occurs before it gets to the end of the tailpipe, and that will be where failure of the pipe will occur ~ unless it's stainless of course.
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L\'escargot.
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The whitey colour was lead dioxide from leaded petrol. Hence you no longer get that.
The black is just the soot emissions from the engine condensing on the side of the tailpipe. A low emission engine still produces a reasonable amount of soot (carbon) when burning. It's simply because while our combustion is currently good, swirl isn't always perfect so at less than maximum efficiency and reasonable gas flow speed you get some incomplete combustion resulting in the soot.
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