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[chipbury]

Hi Gareth.  For what it's worth, I've had my 88" SII Petro 2286cc for 20 years now, and I've religiously documented every fill-up over that time, and recorded every mile. (Sad I know, but I've the time to do it, and worsening fuel consumption is often a good indicator of a problem developing....).

My vehicle is completely standard, no overdrive, running on 205/80R16 General Grabber AT tyres at 30psi, and virtually every run is short.  My nearest petrol station is 3.5 miles away, nearest supermarket 5 miles, the local tip 3 miles, etc etc...

My vehicle runs very well, is serviced regularly, and I use good quality fuel.  It starts on the button, pulls well, has a new fuel tank fitted, and has no petrol leaks that I can see.

My average fuel consumption measured over those 20 years is 16.7 mpg.  The highest I achieved was 18.4, and the lowest was 13.9.

Just thought I'd offer this up.

Interesting to read this as that's similar to my consumption (with same tyre size).  I do hammer along the A roads at 50/55 though which doesn't help!

[Fluffle-Valve]

My Series 3, I monitored the fuel and milage over a year from 1st of Jan to the same a year later. This included towing a caravan to and from rallies and holidays. general running about like shopping, to and from work, taking the dogs out. Basically, I just used it as my normal runabout for a year. It was a 2286 petrol 109 with a Weber Carb. 750 tyres and overdrive and otherwise standard running gear. The Ol'Gal returned 16mpg average over the whole year. Some runs out it was just over 23mpg, but mooching around the town was probably about 10mpg.

It has a TDi in it now, so we are looking at High 20's and over 30 on a run.

[Wittsend]

I'm a little disappointed with all your figures, I would have expected something a little nearer my own experiences.

17/18 mpg on cold short trips.
23/24 mpg on longer trips, cruising at 55mph.

on 6.50 x-ply tyres with overdrive, electronic ignition and a 9:1 CR head.


 :petrol_pump

[Alan Drover]

I suspect Wittsend it's the more efficient cylinder head on your engine that gives the better fuel consumption.

[Gareth]

Yes, 9-1 will certainly help. Both of mine are 7-1, both on Zenith 361’s.

[nathanglasgow]

On a run my Rover 10 88" ex mil 7:1 head, Weber carb, 650 tyres and overdrive will also do 22-23mpg. Again only achieved by staying under 50mph. Possibly the overdrive and Weber carb helps?

[Genem]

Thinks... I shall have to do a reasonable run to see what impact the engine rebuild has had... I have a need to visit Dundee that provides the excuse for a 120 mile round trip, much of which is motorway standard dual carriageway.

[Peter Holden]

On our Rutland weekend I covered just over 400 miles including the 2 days laning and YOD has done over 25mpg.  It consistently clocks 30mpg on road runs.  It did blow a bit of oil out when I thrashed it on the Motorway.

Peter

[Gareth]

That is impressive! Petrol or diesel?

[richardhula]

33mpg on long run from my 12J diesel hybrid cruising at 55mph on 7.50 tyres. Possibly due in part to using the original 2.3 injection pump although no noticeable power loss. 

[Peter Holden]

Diesel Gareth, it is a late S3 5 bearing engine in good condition with 750s and an overdrive.  It has always been consistent at 30 until you go off tarmac

Peter

[Formerlyjeremy]

Motor road tested a petrol 88in soft top in about 1973 and got 17MPG - which to be honest was my recollection from using a family S2a (1966) in the early 70's.

I seem to recall in their handbook before the destruction insructions the Military suggested range calculations should be based on 14MPG - and to be fair that would have covered FFR with large altenators, and other vehicles with the screened igntion which didn't have vacuum advance units.  (As well as service boots!)

[TimV]

Doesn't Wittsend live in Norfolk? The only places to practise hill starts are railway bridges? May that explain the excellent MPG figures?

[Hopeydaze]

Doesn't Wittsend live in Norfolk? The only places to practise hill starts are railway bridges? May that explain the excellent MPG figures?

Good point Tim. I thought your figure was annoyingly high so I assumed all your trips are downhill. I live in Bath, loads of short trips sometimes in 2nd so I average 16 at best.
 Earlier this year I watched as consumption slowly worsened down to 13mpg. This was cured with the carb, distributor and cylinder head removal during lockdown. Conclusion was the 20 year old Luminition electronic timing where the springs on the black disk were broken.
So, it’s definitely worth monitoring your fuel consumption. It will tell you when something’s going wrong.

[Wittsend]

Norfolk isn't as flat as people make out !

On a round trip to Ypres, Belgium my LWT managed just a tad under 24 mpg, some hills were involved.

For sure terrain must have a bearing on your fuel consumption, someone in the Lakes won't do as well as someone in Norfolk.