Hi, I own a Ford Fiesta Titanium, Ecoboost.

In terms of fuel efficiency, is it more efficient to use limiter or cruise control.

For example, in a 50 mile speed limit, should I set the limiter to 50 and put my foot down on the escalator or go into cruise control set at 50?

Many thanks.

It makes zero difference. The car will use exactly the same amount of fuel at 50MPH regardless of weather you drive it with your foot on the accelerator (old school), or using the limiter, or using cruise control.

Remember standard cruise control cannot see what's ahead.  So it will keep the power on even if you're approaching a downhill section.  This is where a driver could lift off to save some fuel.

Likewise at the bottom of a hill, a driver will gradually increase throttle as they approach the incline.  But cruise control has to wait until the speed drops, then dump a load of extra fuel in to get up the hill.

In theory, a perfect driver should use less fuel than cruise control.  But the perfect driver doesn't exist.  Humans are always hampered by some sort of distraction or emotion.

The limiter doesn't save any fuel if you're an attentive driver.  All it does is stop you straying over the speed limit.  So if you weren't over the limit before switching on the limiter, it won't make any difference.

Having said all that, I would recommend using cruise control in a 50mph section.  It leaves your mind clearer to focus on other hazards.  It saves the strain on your foot.  And cruise control won't become tired and less efficient as the journey goes on...

17 hours ago, TomsFocus said:

Likewise at the bottom of a hill, a driver will gradually increase throttle as they approach the incline.  But cruise control has to wait until the speed drops, then dump a load of extra fuel in to get up the hill.

I don't know if all Mk 8s are the same, but in my current (and previous) one you can really feel a "surge" on an up slope. It's most noticeable on a gently undulating road where driving "manually" you go with the flow as you suggest. I suspect I get very slightly worse consumption in those circumstances with cruise versus "diy". 

Certainly found no mpg benefit with the speed limiter either (assuming you're driving at or below the limit anyway, of course) but it might save on the cost of fines or speed awareness courses! As posted elsewhere, I have found the "intelligent" variety I have on the current one pretty good, but you still need to remain alert as it is by no means infallible.

I guess some people might find benefit from cruise. I've never had particular difficulty maintaining a constant speed**, but I often come across folk whose speed fluctuates 10mph or more either way. They're usually the same ones that also constantly drift between the kerb and the white line on a straight road.

**No I'm not claiming to be a perfect driver, my parallel parking is awful!😀

 

There's nowt better than your right foot