Fuel efficient driving.

Limey

almillar wrote: »

Coasting and freewheeling is the same thing. It's rolling along without a gear engaged (ie in neutral or with the clutch pedal pressed). Idling petrol used.
You need to separate this from simply taking your foot off the accelerator whilst in gear. This cuts the fuel in most injected cars, but is 'stalling' the car and the engine stays alive through the movement from the wheels connecting it through the gearbox. This running of the engine causes drag and makes the car slow down. This can be useful for holding the car back when going down a hill instead of the car running away with you, or melting the brakes!
So when deciding what is more fuel efficient, you need to decide 'how quickly do I need to slow down?'. If you're approaching red lights - are you going to stop? Keep it in gear. Are you going to make it through? Let it roll, planning to accelerate again just as the lights change when you approach the junction.
Judging these situations well is very good driving, can save big stops and starts (or at least slow-downs and speed-ups) and save loads of time and fuel, and wear!

My old Saab 96 (1975) used to have a 'freewheel' lever which when pushed down disengaged the clutch (i think) whenever you took your foot off the accelerator. Whether it was for fuel saving or as a 70s form of traction control I don't know.

Needless to say it was f'in scary when used on the motorway (only tried it once). :rotfl:

skiddlydiddly

Done a fair bit of this lately, training others to get more mpg.Have seen varying results but all have increased their economy significantly with the worst being approx 30% and the best being by approx 250%.

grizzly1911

I have been driving just over 30 years.

I started with 1.3 Austins/Vauxhalls with carburetors and mechanical electrical points for the spark management. They had top gears of 16mph/1000. power aof aroun 55/60bhp averaged 30mpg maybe 35 on a run in the country - remember them.

I have driven Diesels for close on 20 years now and wouldn't go back to petrol if I had a choice. I appreciate that for some ultimate luxury performance machines they do not fit in .

First Diesel was a Ford with the 1.8 indirect engine, 60bhp presume gearing of 22mph/1000 and it did 50mpg what ever you did to it. Second was a Xantia with a 1.9 XUD engine 70Bhp, 20mph/1000 and it did 47 mpg again it did not vary.

Third was a Citroen with the 2.0HDi engine - 90bhp (no turbo) and it varied quite a bit 44 -54 depending on where how it was driven.

I then had an Astra with a 1.7CTDI engine which was eco friendly 107gCO/100 -80bhp, low blow turbo, (dirt cheap on the BIK) but with useful performance due to lowish lower gears. They only put this engine in one model it had a lowered ride height and a thin/discrete boot wing spoiler, 30mph/1000 in top. worst was 55mph, more often than not 60mpg and over 5000 miles one month of motorway cruising 64mpg. For some reason they didn't seem to reuse this tune profile elsewhere.


I now have a toyota with a 2.0D2D engine, 126bhp 37mph/1000 average 47mpg but around 54mpg on main roads/motorways.


We also have a Corsa 1.3CTDI eco flex, brought for economy & £35VED. This has 75bhp and 26/7mph/1000 and whilst it will do high 40's running around it hasn't bettered 54mpg yet which is a lot less than the official figures. Disappointing after the Astra. Maybe it is a relatively big body but performance seems OK for the spec.

It is interesting to note that the modern Diesels give much improved performance but variable economy and I am sure that the "best" figures are in a large part down to the high top gears which enure the turbos aren't working too hard and the electronic engine mapping. Whilst not a fan of spoilers as such, interesting that they took time to put one on the Astra, breaking up/smoothing the drag must have contributed.

Grade_A_Reject

You could try this Top Tip pulled from an early(ish) issue of Viz.

Save petrol by pushing your car to your destination. Invariably passers-by will think you've broken down and help