What's the consensus about economical driving in higher gears vs. doing harm to your engine in the long term?

 

I have a 6-speed 110 TSI engine and usually drive in 4th gear at 50 kmh (31 mph) but sometimes drive in 5th gear at that speed as well.

In 4th gear I believe there's around 1600 rpm and in 5th around 1250 rpm or so if I remember right.

 

Obviously, the fuel consumption improves with less rpm, but it seems the engine still prefers to be driven at 1300 rpm and up, rather than less -- at least from how it feels when your foot is on the pedal.

 

Yes, I know it will suggest automatically when to lower the gear, but from what I remember it only does so when the rpm drops to 1000 or even below that. Anything below 1300 rpm already seems pretty bad to me, I mean it feels like I'm not doing any good to the engine in the long term -- especially in terms of grime accumulation inside the turbo (for the lack of better wording). Or am I wrong?

 

I was told by a local dealer that every now and then I should rev it a bit higher (i.e. speed up fast) to "clean the engine up" a bit.

 

So is there any consensus on all of this? (Please don't tell me to go with whatever feels best in terms of putting labor on the engine when my foot is on the pedal.)

Lower revs doesn't always equal lower fuel consumption, if you're in too high a gear the engine will be labouring on a higher throttle position meaning more fuel is being put into the engine that can't be burnt correctly because of the higher gear therefore being wasted.

My experience is only with a Polo 1.2TSI 110PS and that car has a economy gear change indicator, so really believe that if your car has one, also from the car data read out you can check the current average MPG and I think the instantaneous MPG on the dashboard display (maybe not on that car, forgotten). That does seem to tie in with what I feel is the time to change up and down.

jon, the gear change indicator lights often lead you to change gear too early. This wastes fuel as Gaz is saying. I've found ignoring the gear change indicator produces better fuel economy, and so have many others on here. You really don't want the engine to be labouring at too lower revs. It's not efficient. 

Seeing as how cars are all different, and locations and journeys and drivers style, 

try driving in different ways when doing a trip.

 

Brim the tank.

One journey drive naturally and safely concentrating on getting where you are going.

Brim the tank, see how much fuel you used.

 

Next trip drive safely and spend the time hypermiling, driving the way you think is economic.

Brim the tank, work out how much fuel you used.

 

Then you know. 'Whats the worst that can happen?'.

As above. Low revs isnt always better for economy and certainly isnt always good for the engine. Labouring isn't good at all.

A light throttle at a higher rpm uphil can be better than a heavier throttle, labouring an engine at low rpm.

Unless its something really powerful, which will pretty much pull any RPM anywhere and still accelerate nicely.

Yes, as above makes more sense as sometimes if you are using the gear change "suggestion" and are reading the road ahead, which we should all be doing, what is being suggested by the indicator will not make sense, I've even found that when on a light throttle at the top of a slope, the suggestion will be to change down twice at a time when the engine is not labouring as the anticipated "engine labouring stage" was not reached before the top of the slope was reached, then the engine loading dropped.

 

Really for a competent driver, at best the gear suggestion indicator might just be seen as a reminder to change up as the engine noise might be lower than what you had previously been used to, initially I switched that feature off when I got my Audi S4 - mainly due to me noticing a "screen change" out of the corner of my eye when the nagging "change up" indication appeared usually at an important point in the journey, ie more important things to take care of at that time, but now that wife's new Polo has a gear change indicator I have switched it back on!

 

Though if you are just driving to get from A to B and admit to being a car driver license holder and car user as opposed to being a motorist - then yes maybe you do need this help to save the planet and the engine.

My understanding is that the fuel efficiency of an engine is related directly to its torque production.  If a graph is produced showing torque against engine speed, the curve for fuel consumption will generally be a mirror image of that for the torque. Here's a link that should help explain better: http://www.hotrod.com/how-to/engine/ctrp-1304-understanding-volumetric-efficiency-and-torque-relation/

 

Though it can be seen that the most fuel efficient speed for the engine itself is generally the speed at which maximum torque occurs, air resistance and rolling resistance plays a part in the fuel efficiency of the car as a whole of course.  I don't have sufficient experience to comment on this aspect other than to suggest that keeping the engine speed reasonably close to its maximum torque band should give the best overall fuel efficiency.

I suggest to keep revs around 1600-1700 and above all time, it's not good for such a small engine to go below that. If you had a V8 then around 1400-1500RPM minimum would be ok.

If you try to save every penny and keep the revs below 2000-2500RPM all the time you will definitely have some engine problems later in the long run. Engines need to 'breathe' so flooring it occasionally is only good.

 

Tõnu