Define "sludge".
If you're seeing "Mayonnaise" then you're not letting the oil get up to full operating temperature (cold starts, short drives etc.) The 'mayonnaise' is oil and water mixed and emulsified. If the Oil got significantly over 100°C (as it should) for a nice sustained period of time, the water would boil off, leaving oil.
Water is a typical by-product of combustion as well as ingressing from other sources, and a fair amount of it gets into the oil. If it doesn't boil off, you get a creamy-coloured goo, which typically collects near openings to the outside world... the oil cap, the dipstick aperture and crank breathers are favourite places...
If this is what you're talking about, it's not "sludge" as the rest of the world understands it.
Mayonnaise-like creamy goo collects ABOVE the surface of the oil. Sludge collects INSIDE the oil, and BINDS the oil.
So whatcha talkin' about? Which one?
-And if you're talking about mayo, then yes.. your problem is that you're not letting the car get warmed-upm and driving too short distances for the condensation/H2O contamination to boil off.
Keith