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Does premium diesel fuel improve FE? I'm talking about comparing standard diesel fuel with Shell's V-Power diesel/BP's Ultimate diesel, which apparently has a higher cetane rating than standard fuel. Looking around online, I seem to get the impression that it does increase FE, but only slightly, and not worth the extra cost. What's your thoughts?

Thanks for your time!

My understanding is that a higher cetane rating means combustion starts a bit sooner. So in effect you'd get slightly advanced timing, which usually helps mpg a bit. There are additives that claim to do the same thing.

I've never seen a station around here with "premium" diesel. Is cetane rating the only difference they're advertising, or is there a difference in things like gell point, lubricity, etc.?

They add more stuff such as cleaners, and make the fuel in a slightly different way I think. Have a look here, for Shell (http://www.shell.co.uk/home/content/gbr/products_services/on_the_road/fuels/v_power_diesel_pkg/advanced_performance_fuel/advanced_performance_fuel.html), and for BP (http://www.bp.com/sectiongenericarticle.do?categoryId=4005616&contentId=7009018). It's interesting to see Shell refuses to claim an increase in FE, they said "Maybe", but BP does. However, I think BP has a higher cetane number than Shell.

Overall, I don't think the extra miles justify the extra costs, seeing it's $5.60 for an US gallon of normal diesel, and $6.23 for an US gallon of premium diesel from my local service stations.

It's quite easy to get premium diesel here, probably due to diesels being a lot more common here.

I can't say if it's because of cleaning additives or higher cetane, our 2 cars are running better since we are using only higher grade diesel.

In megane I could barely stay at 1500rpm in 5th. Quickly after the 1st tank I could accelerate from 1400rpm and now I can do it from 1200rpm, and 1100rpm if engine hot and on flat road.

In scenic my wife had some "holes at acceleration". They disappeared during the 1st tank.

Now we are saving more than the over cost so we continue to use it.

Denis.

With the cheap diesel fuel I use my car is actually happy to cruise at 900rpm in 5th gear, and I can even accelerate, just very slowly. However, I don't think this is fuel efficient as the engine rumbles just slightly when accelerating, so for now I am doing a minimum of 1400rpm in 5th gear until I get the MPGuino installed and I get a better picture.

I'm going to be commuting over a hour away, so I've decided to do 2 tanks to get a baseline as it'll be 95% motorways, then do a tank of the premium diesel, see what difference it makes, and I'll report back, however it will take quite a while.

Thanks for your comments!