Thanks for your reply, I wasn't trying to give bad advice, I was pointing in another direction.
You say it measures unburnt fuel and I agree, however engine oil is just a few stages away from petrol in the fractional distillation column, all it takes is a lot of heat to turn engine oil into petrol in laymans terms.

Because Engine oil has 3 times the ammount of Hydrocarbons than petrol it would only take a bit of Oil being burnt to mess up the exhaust emissions. granted it needs a high temp to do this but we are talking about internal combustion under pressure.

Its just another way of looking at it but I don't intend to get in a fuss over it

Nick