The new VW Diesel Hybrid, the Golf TDI Hybrid may end up getting 69 mpg (using the European scale). That's really good, considering the current mpg leader, the Toyota Prius, gets 54 on the same test. Diesel engines are more efficient than gas engines, resulting in better fuel efficiency. And so tying diesel together with an electric engine is a no-brainer, right?
Well, not if you throw in any sort of economic sense, it isn't.
It's the same thing you always see, when people start talking about hybrids and diesels. Diesel engines are more expensive than gas engines. Gas Electric Hybrid engines are more expensive than gas engines. Put the two together and you get twice the expense.
Source:VW gets great mileage from diesel hybrid, cost is a hurdle - Mar. 7, 2008
Diesel engines burn fuel using high pressure and heat instead of a spark. The engines have to be more rugged to withstand the strain, so they're more expensive to build.
The other issue is diesel fumes. The new strict guidelines forced diesels out of the US marketplace. But new, cleaner diesel fuel along with restructured diesel engines are going to allow them back in, probably in the coming year. But that new design structure is going to cost you more.
BTW, in case you're wondering about the European marketplace (i.e. Aren't diesels more popular in Europe? How come?) It's because diesel fuel is less expensive than gasoline. The Europeans have increased gas prices steadily to the point where diesel is more cost effective than gas. It's also forced the market into smaller cars.
So, next time you see a diesel to hybrid, keep these points in mind.
About the TDI Golf Hybrid: It may be sold in Europe for years before it would cross the pond to the US. Unless gas prices change to the point where it's similar to what we see in Europe, or diesel engine costs come down, it's just not going to make sense for VW to bring it here.