Thread: TD5 ideal speed for best fuel consumption

Originally Posted by Studio54

I don't drive my manual that conservatively and I get 830 to 850 around town every time.

Around 95 is the best speed for economy and at 110 it does drop significantly.

If you could stand doing 90 on a long stretch with out to many demanding hills and obvioulsy not towing I rekon she would be good for a rio. (1000Kms)

youd have to drop back to below 80 for that and you wouldnt want to run into a hill or tail wind then you might just break the 8l/100km mark....

I went close once but I had a lot of other things working in my favor (like draughting an 80t crane all the way) and still only got down to 8.5l/100km

Originally Posted by hiline

i remember seeing somewhere

90k's was mentioned

thats all round touring with or without loads

90 for DRUT as well

Originally Posted by Studio54

I don't drive my manual that conservatively and I get 830 to 850 around town every time.

Around 95 is the best speed for economy and at 110 it does drop significantly.

If you could stand doing 90 on a long stretch with out to many demanding hills and obvioulsy not towing I rekon she would be good for a rio. (1000Kms)

Gees! That consumption is substantially lower than pretty much every Td5 owner I know. I thought I got good consumption around town by get 10.5l/100km!!

Angus

At my time with Mobil (Now Exxon Mobil) we did extensive research/analysis of (as it was then MPG)

Now bearing in mind that this was over 20 years ago.........

Across the range (ie from 1.2 ltr to 3.5 ltr) - remember 3.5 litre was considered a 'big' engine in the UK

The most ecconomical speed was 56 mph which is 90.1233 km/hr.

..............however this was 20years ago, engines have become more effecient since then (okay maybe Landie engines haven't)

...........but seriously there must have been efficiency gains since 1983 - so I would assume that the most ecconomical is slightly greater than 90 km/hr -----but not much greater.

And this is assuming 90% highway/freeway/motorway/tollway (whatever) and 10% town traffic.

Originally Posted by mcguckiana

Gees! That consumption is substantially lower than pretty much every Td5 owner I know. I thought I got good consumption around town by get 10.5l/100km!!

Angus

bet hes talking speedo speed tho which on average across all defenders and discoveries Ive been in is 8kph faster than indicated... so his 95 could well be my 88...

This is all fine with many reports of 10L/100k, but were do I start looking to bring down my consumption from 13.2L/100k? This consumption has been averaged out over the last 15000km! This has ranged between 11 and 14.5 per tank, depending on the driving, towing a camper trailer to commuting to around the shops.

The vehicle is a standard '99 TD5 discovery fully services with 135,000 on the clock. (standard tyres 255/65R16, no registered ECU faults, no excessive exhaust smoke)

I have been looking to have the ECU remapped but have been holding back due to the higher fuel usage at the moment. The extra torque should make to towing a lot less of a drag. Will this increase fuel usage?

When mentioning the high fuel consumption at the service I was told not to worry unless it was below about 600km to the tank (full to when the light comes on). Is this another way of saying that it could be one of many things and that the cost to track the high consumption is not worth it?

So where should I start to looking for to bring this down to a more respectable number? (and parking it in the shed is not a suitable option)

Originally Posted by Big D

This is all fine with many reports of 10L/100k, but were do I start looking to bring down my consumption from 13.2L/100k? ...

Hi Big D,

From my experience:
1. Driving style: easy start, change gears earlie, <90km/h on highway
2. Air filter: are you sure it is clean and been replaced at last service?
3. Bad quality diesel: change your favorite service stations/brand
4. Might be worse to try something like flash lube diesel conditioner to clean injectors (3-5 tanks to get result)
5. Increase tyre pressure up to 40psi
6. Check for fuel leaks
7. Does your vehicle rolls OK downhills?

Cheers,
Ruslan

ANY engine in ANY vehicle performs at it's most fuel efficient while at maximun torque, which in the TD5 is 1950rpm. Cruising at 1950 in 5th will give your theoretical best consumption figure, but as the torque curve is close to max Nm a couple of 100rpm either side of 1950, then effects of wind drag come into the equation. (ie It may be possible to drive at 2200rpm and still be close to max torque, but the wind drag will be higher.)