How to get better MPG.. I know we drive a truck engined brick BUT!

[Alrightchief]

I've read in another forum about a Cherokee, that was modified, mostly the underbody, panels were added to specific spots to improve the aerodynamics. From the exterior the car looks like unmodified, but with these mods, the guy got improved it's fuel economy from ~19mpg to ~30mpg. He posted about the aerodynamic simulations he made and the test results. If you are interested, I can search that thread and post it here.
Other than that, I am planning to do the same for my J95 D4D, I will model the whole underbody and make a few flow simulations, and I will modify the sub according to the results. If you are interested, I will post the whole process with the model, pictures and test results...
In the engine oil I use Metalube, it smoothed out the engine, I also use Metalube fuel additive. I used this stuff on all my cars, I have several hundred thousand of experience with these products and I love it. I will put in my diffs also soon.
With my stock car, using the additives I get 28.34mpg traveling at 68miles/hour.
The car: J95 D4D 3.0
4 speedAutomatic transmission
265/70/R16 tyres

That is a point I have all my panels off at the moment so that's interesting! I also would be interested in seeing the research you conduct!

 

[Gary820]

I've got plates underneath to smooth out rocks

 

[Grimbo]

Underbody airflow has a huge affect on drag .....probably more so than adding spoilers or roof racks .

Drag coefficient is not a straight line and much like noise the curve steepens rapidly with speed .

On a 4x4 it's also difficult to improve or manage it ( certainly with 2 live axles )

The higher off the ground the harder it is to smooth the flow and the air is very turbulent ....thats why race/rally cars are low and have splitters and diffusers front and rear and they do make a massive difference .

We had some armoured 105's that had full underbody protection plates that were under the chassis so apart from the axles the underside was very smooth . This however was fully negated by the fact it was well over 1 ton heavier (some of them 2 ton ) and MPG was of no concern .

The Mrs performance Merc Estate has a very full undertray with lots of air management tweaks , vents , etc and no doubt fitting a 4x4 version to the cruiser could help a lot but would be very vulnerable and.........................
TBH I didn't think of MPG when I purchased a giant 4x4 with live axles and 3 diff locks , raised it 2 inches , stuck very high rolling resistance tyres on it , and proceeded to tow 4 tons (off road of course) .

 

[stumog]

Agree not the first point but a good argument as to why you need to spend £600 on some plates

 

[Paulajo]

I'm with Ian and Jacob with around 23, running 265/70/17's GG at's . 5 spd auto too.

I'm with Ian and Jacob with around 23, running 265/70/17's GG at's . 5 spd auto too.

I have a 4.2 TD Auto, 1998. I get 30+ mpg around London with gentle driving.

 

[Michael Montgomery]

1hdt motor, intercooler and large exhaust, rebuilt fuel pump and new injectors, 5cm lift, larger tyres and 400kg plus of overland mods including rooftents etc.

Fuel economy not good 20mpg driving in the real world without ones foot to the peddle.

All these mods I recon take away around 5mpg easily in my opinion.

Having fuel rise there by over 40% this year because of the Turkish currency crash.

What can I do, earn more in income to fill it up or drive it less lol

 

[Sarge001]

For me, it is not that important to have a heavy under-plate as I don't go on terrain that can touch in any way the under body, so even an 1 mm aluminum sheet would do the job. due to the design of the under body it is very easy to fit. As I go on long journeys, mainly on highways, for me the mpg is important.

 

[big-yin]

Interesting thread : I'm coming to the end of my first tankful (99 4.2 TDi Auto) and if I'm lucky I'll end up with 21/22mpg average over 75litres and 330-340miles. I was hoping to get 25mpg so i'm not that far away with mostly town driving as I live a mile from work with a few 10-15mile trips with family thrown in. Still rather this than a boring company car

 

[moggy1968]

The reason race cars have splitters, undertrays etc is nothing to do with fuel consumption, which is rather immaterial to them. It is to do with making the go faster in a straight line and/or to push them onto the road for improved cornering grip.
An F1 car for example actually has a pretty appalling drag coefficient!
As mentioned, the weight of an undertray on a 4x4 will probably negate nay aerodynamic gain. Weight is the real killer. Sticking a RTT on mine didn't help much either, knocking off probably 17%!!

 

[Michael Montgomery]

One way to get better MPG is changing the fuel source. When I ran SVO for 3 years I didn't care much about MPG as its cost next to nothing to run the diesel motor. With this in mind drove it a lot more feeling the true freedom it brought however some complications and now wiser to do it better back on the diesel counting the cost lol.

If I was in the UK id probably get a 100 series petrol with LPG as the best bet in conventional terms.

Over-landing RTT & accessoires ran at 20MPG 14/100KM
Without recently was getting around 22MPG 12.8/100KM