Im a newbie to the diesel world I just bought a 2010 tdi wagen 6 speed manual 18 inch wheels , ive only got 3000 miles on it and dont get but 31 mpg in the city 39+ on the highway , is this normal I assume it will get better. also anybody know where to get the best diesel in cincinnati? Also the dealer told me never to use biodiesel is this correct?
The fuel economy will improve as your JSW gets more miles on the odometer. You will also see more MPG when spring gets here, with quicker engine warmups and an end to the winter diesel blend. So yes, the current numbers you're observing are reasonable for a new TDI in a northern climate.
As for biodiesel... it is safe to use a 2% blend, aka B02. This would provide a bit of additional lubricity to the fuel, so would be good for all the fuel system components. B05 is less safe, and VWoA strongly discourages any blend greater than B05.
During the regeneration stage of the diesel particulate filter (DPF). raw fuel is injected into the cylinders and then flushed through to the DPF without igniting until it reaches the DPF. Some of this fuel can attach to the cylinder walls and be scraped down into the sump where it mixes with the engine oil.
Regular petroleum fuel, in small amounts, does not harm the lubricating qualities of the motor oil; but molecules of biodiesel tend to attach to metal and not allow either the base oil or the anti-friction additives in the engine oil to reach the moving metal parts.
If you must use a biodiesel blend of 5% or greater, then you MUST shorten the oil drain interval. Instead of changing the oil every 10k miles, you may need to shorten it to 5k miles or even 3k... which is necessary but can get very expensive.
Edit: I would also mention that the 18" wheels/tires will prevent you from getting the maximum fuel economy your JSW is capable of. There is a tradeoff, because those tires will give you better grip on the road -- but grip is just another name for friction. And the wheels and tires themselves are heavier, so it takes more energy to start them rotating. So the weight of the tires and wheels is more of a factor in stop-and-go traffic and not a factor on freeways and expressways.
