Suggestion 1. Color bars based on fuel.
On page http://www.fuelly.com/car/peugeot/308 is a barr. What is showing avarage km/l. Can this bar changed, so you can see in one eye withs car is running on gas/diesel/lpg.
Suggestion 2. Add option to filter engine types. All diesel to show L4 and H4 combined. and All gas to show gas,H4,L4
We already have filter controls at the top of the page. Look for "Filter to:" under the page headline. Color coding is an interesting idea, but I'm not sure enough people are interested in seeing the distribution of fuel types. And if they are it's easy to use the filter controls.
We combine fuel and engine types into the same filter to make things easier. I think most often folks are interested in a particular version of a car, not necessarily a particular fuel type across different engines. I definitely can see how that would be neat in very specific circumstances, but we're designing for a large audience and we have to keep ease-of-use in mind. It'd be more complicated to choose three different options whenever you want to filter the list.
It doesn't have to be mixed by other fuels right now. Have you seen the filter controls at the top of the page? They look like this. Use those controls to limit the bar chart and listing of vehicles to the specific properties you're interested in.
It's true that people can enter whatever they'd like about their vehicle. And people often get it wrong. We don't want to force people into specific choices because managing every possible correct combination of options across all models would be too much hand-holding for our small operation. So yes, a couple folks put Diesel L4 which doesn't exist, but what's the harm? They're not included in a particular sort.
Let's give people the benefit of the doubt and assume they have a very good reason to choose Diesel L4. Maybe they have a modified engine with an extra cylinder. In that case you wouldn't want them grouped together with the other Diesel engines because it's significantly different.
Keep in mind we're looking at a specific case here of a specific model. When you get to something with more people reporting, like the Jetta, the number of wrong entries is very small compared with the majority. We need to design for the majority of cases—and I'm not sure fuel-type alone is useful without also including the engine type.