<VV> Engine checking by the exhaust

[Daniel Monasterio]

    I have been using, by many years, a rudimentary way to check the condition of an engine by finger testing the deposits at the exhaust pipe. Taking a sample with a finger I find:
1.- If there are only grey traces (almost nothing on the finger), the engine has a good combustion and no oil burning.
2.- If the deposits paint my finger with a black and dry coating, the engine is using excess of fuel but no oil burning.
3.- If deposits are black and sticky, means oil burning.

    I don't remember when started this way nor why but, would like to know if I am right or wrong. 

    Thanks

    Daniel Monasterio