BMW 328i GT – A Luxury Car

Our man crunches the numbers to justify choosing petrol over diesel

Black or green? Or should that be silver or blue? That was the choice I faced when we were offered a BMW 3 Series Gran Turismo for our fleet. The silver car is a 318d diesel, while the blue one is a 328i petrol.

Seeing as 11 of the 15 cars in cars in the Auto Express garage are diesels, a petrol somehow seemed more interesting to me. The fact that the 328i cover 0-62mph in 6.1 seconds – that’s 3.6 seconds quicker than the diesel had nothing to do with my decision. Honest.

BMW is making a big deal about its new, downsized petrol engines

Also, BMW is making a big deal about its new, downsized petrol engines. Not so long ago, choosing the 328i would’ve meant a thirsty straight six. But today you’ll find a 2.0-litre twin-turbo four-cylinder under the bonnet. Okay, it’s still not as economical as the 318d (which does a claimed 62.8mpg), but the promises figure of 44.1mpg is acceptable, considering the performance.

If you read Auto Express every week, though, you’ll know that the cars on our fleet always fall shy of the manufacturers’ claimed figures. In our experience, downsized petrol turbos are among the worst offenders. So, to validate my choice of engine, I devised a little experiment.

Eco Pro mode help boost turbo’s economy

Before I took delivery of the 328i GT, we had a 318d GT in the office to test. I drove it from London to my mother’s home in the West Midlands, and over the 100-mile journey (which was mostly motorway), I averaged 52.3mpg. For the return journey, I swapped into the 328i, and as I arrived back in London, its trip computer read 44.8mpg.

I may have been a bit more tentative with the throttle in the petrol car, subconsciously trying to justify my decision. Also, I ran it in super-frugal Eco Pro mode. But that doesn’t matter, because I had proof that the 328i GT could do what BMW said it would do.

I’ve calculated that over the course of six months, covering an estimated 5,000 miles, choosing the petrol model should cost me an extra $114. That’s a small price to pay for the far smoother, quieter and faster car.

Mat reckons petrol engine’s performance and refinement are worth the higher running costs

Sadly, it’s not going to work out quite that simple. As our spec panel (left) shows, our overall average economy in the 328i so far is not 44.8mpg, but 28mpg. The reason for this? After my initial motorway economy run, the 328i was driven much harder for the following 600 miles. And that’s the problem with these small turbo petrol engines: they can be very frugal if driven sedately, but it’s almost impossible to resist thrashing them. And when you do, they drink fuel at an alarming rate.

So, a quick recalculation of my running costs based on the poorer fuel economy figure shows that choosing the petrol car instead of the diesel is actually going to cost me an extra $711 over six months. Maybe I didn’t go for the right-colored pump after all. Still, at least I should have fun finding out…