Diesels can also 'make' oil due to leakage of diesel past the piston rings. This is particularly likely in cars with DPFs if they perform a lot of active regenerations as these cycles require unburnt fuel to pass out the exhaust to burn in the DPF. A byproduct of this (as well as increased fuel consumption) is that it is far more likely for liquid diesel to end up on the cylinder walls and for some of this to get past the rings into the sump.
The final effect is that your oil is thinned out and you are more likely to suffer from wear in heavily loaded bearings. I suspect that this is the real reason VAG won't allow high percentages of biodiesel to be used as oxidation of biodiesel in the sump would have far worse effects.
Have a read of this http://subdiesel.wordpress.com/2011/...dilution-graph and if you're really interested, http://www1.eere.energy.gov/vehicles...jundaswamy.pdf
Last edited by kaanage; 18-09-2013 at 06:52 AM.
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VW - Metallic Paint, Radial Tyres, Laminated Windscreen, Electric Windows, VW Alloy Wheels, Variable Geometry Exhaust Driven Supercharger, Direct Unit Fuel Injection, Adiabatic Ignition, MacPherson Struts front, Torsion Beam rear, Coil Springs, Hydraulic Dampers, Front Anti-Roll Bar, Disc Brakes, Bosch ECU, ABS
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