Thread: 3.5lt EFI day to day fuel economy

Was the rear bar, bull bar, tyre carrier, etc added after your last economy checks or have they always been there? I would have thought somewhere between 17 and 20 would have been about right overall, with 14 ish on the highway.

The fuel usage on my 3.5 moved up as the KM did and by the time I replaced the engine (at 380,000KM) I couldn't get under 20 with it.

Haven't managed to do a long enough run with the new engine to get a baseline on it though.

Yeah all were there. The light bar is the only addition and I have folded it down at the moment to see how that helps.

I can't accurately tell how many kays the engine has done and I might try and do a compression check to see how worn she is. That may be the key and a rebuild be on the cards

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Reduce your tyre width to standard and watch those consumption figures change instantly.

See that's the thing. The old economy figures are with those tyres. In 2011 prior to the lift and tyres, I would get about 470-520 kays per tank. After the mods that only dropped to a maximum of 480 kays per tank and I could get that no matter where I was driving. The biggest difference I noticed was taking off and feeling lagy up hills.

In late 2012 back down in Adelaide I noticed the extra usage and I could only manage 400 kays to a tank. Then after the trip back up here and currently, I am getting 330 at the very most. Makes for a nervous trip to Darwin..

I have pondered the idea of going back to a 265 all terrain for the next set of tyres, but like I said, this didn't start with the change in tyres.

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I was just using it as an example.
some years ago I did a 2 tank test on 4 different sets of rims & tyres on my 560SL.

standard rims 15x7 with a 205/65VR15 michelin
AMG aero monoblock 16x7.5 with a 225/50ZR16 michelin
AMG aero 3 pc staggered 17x8.5 & 17x10 with 235/45Zr17 and 275/40ZR17 Falken 452
W211 E63 AMG monoblock 18x8 & 18x9 with Yokohama AD08R in 235/40R18W & 265/35R18W

On standard rim/tyre avg 16.5L/100
On 16x7.5 rim/tyre avg 18L/100 (it was 17.89, so round up)
On amg 3 pc, avg was 21.3L/100
On E63 mono's avg was 20.5L/100

This was over 2 tanks of fuel, consecutively over a period of about 6 weeks. The route was my 134km commute (round trip) each day which is an almost perfect combined cycle city/hwy drive.

I did the same thing in a 190e 2.6 auto I owned for a brief period. it had same 15x7 OE alloys with a slightly smaller profile (55 series, same width Bridgestone RE001) and my wife drove it and would routinely get 9.0/100 If I drove (thrashed) it, the car would return between 10 & 11L/100.
I changed the rims to 18x8 and ran a 225/40R18w michelin and the consumption with my wife driving went to 11L/100 and mine went to 13.5L/100
This was noted over a period of 7 months. 4 of those with the standard wheel/tyres and 3 with the big rims.

4 weeks ago, I changed the Cooper 225/75R16's on my RRC to Mickey T STZ's 245/70R16
fuel consumption has gone up nearly 2.5L/100 with the same (reasonably hard) driving.

So the tyres are playing a role in your fuel consumption. Whether or not they were the same before is not the issue.

Having said that, there has to be a more mechanical issue, unless you have changed the frontal area or altered the external attachments / cargo to increase your drag coefficient.

When was the last time you did a complete fluid service on the vehicle? sudden increases in consumption can often be found in the lubricating fluids - whether it be metal deposits or burnt deposits or a change in smell...

wheel bearings? last time you lubed / serviced them?
Brake pads & rotors? dragging? possibly another reason.

Anything that can increase the rolling resistance of your vehicle (i.e. in the drivetrain) that has been changed recently?

It could also be the 'flapper' playing up. Which others have probably mentioned before. I'm not an expert on the implementation of LH jetronic on a range rover, but it was a common problem with EFI'd black motors in holdens of years gone by.
Also cold start sensors, and fuel pressure regulators can cause issues, sticky injectors..... list goes on and on and on.

Possibly the only way you will be able to be sure of it is to systematically go through the vehicles electrical, fuel and lubrication systems, then look at the actual drivetrain mechanicals themselves if a full fluids flush and service doesn't go some way towards improving the economy.

You might be surprised what a fluid & filter change can do on a transmission and transfer case. I knocked off 1L/100 when I flushed the BWTC, and was surprised to see some metal in the ATF. the 4hp22 was in excellent condition, as it had only been overhauled a couple of years prior to my owning it, and low km since.

I replaced diff, swivel and wheel bearings were lubed, did a complete top-end foam clean (upper engine - threebond) as well as a heavy fuel system clean/flush with some liquimoly flush.

Now, It didn't net me a huge efficiency increase, but it did better the mileage by 1.5L/100. The real bonus was that the whole vehicle drove better, more smoothly and much quieter than it did before.

and fwiw, this is a vehicle that in the p.o's hands was serviced every 5000km on the dot for the last 11.5 years at a very reputable sydney LR specialist.

Given your somewhat 'noticeable' increase, and noting that you have stated nothing has essentially changed from then until now, I would simply spend a whole day one weekend, going over the vehicle and doing all the little lube-tasks that you'd normally do on a major service.

belts, coolant, ignition (plugs / leads? / cap / rotor, check timing) fuel & oil filters, oil change, diff / gearbox / swivels / bearing lube, flush brake fluid, check rotors & callipers & pads, lube uni joints and sliding joints, check battery (if you have one that's not maintenance free) air in tyres etc.....

If all that's done, and you have a good handle on where things are at, then the next step is to start looking at the internals of the engine, transmission and transfer case. You'll know the best place to start when you check the fluids form each major assembly.

Oh.... almost forgot. I'm not a huge fan of 'flashy brands' of oil and stuff like that. I do use a very high quality oil in some of my cars though.
As an aside, when I did my last engine oil flush / refill in the RRC, I also put a can of liqui-moly's MOS2 additive. Now I'm not saying it is going to do anything miraculous to your engine, but as a friction reducer, moly disulphide is well known. It did quieten my tappets down a little. not much, but noticeable.

You never know - sometimes little things can have a big effect over time. I'm going to see what changes (if any) the additive makes over the next 5000km.

anyway, thats enough of my ramblings. whether you found it useful or not I guess is a bit of a moot point now - if you read this far

My old '86 3.5 flapper Rangie with 600+k on the clock, 5-speed, 245/75-16 AT's, bulbar, spotties, roofrack, ARB rear bar with wheel carrier......day to day average is low/mid 14's. Will get better on a trip.


My 3.5 auto D1is a little worse, averaging 15.4 day to day driving.

Rick1970: Your Disco is about where my rig used to be. And it's not that I expect to be getting that, im ore concerned as to why I'm not getting it anymore.

Mercguy: I read your reply and you make some interesting points.

The tyres I have fitted and have been since mid 2011 are Kumho Road Venture MT's. I would say I have damn close to 100k on them now and at least 30k of those have been on dirt, in the mud and climbing up/down something.

I'm pretty on top of tyre rotation and pressures. I run them high(38 front-42 rear) to compensate for no roll bars and the fact 100kmh is the average speed to and from work. It has worked well for me and I practice this with vehicles at work and for friends/family.

Last service was August 2015 about a month after I did the new exhaust. That consisted of new leads and coil, eng oil, air filter, fuel filter and eng filter. Replaced the little breather filter behind the throttle as well as cleaned out the flame trap on the right side rocker cover.

Since 2004 I have used Penrite oils in everything I own. This service I tried out a 25w/60 to see if would help with compression, especially on first starts with the hotter weather up here. It actually made the economy worse for about 2000kays! The oil change prior was at Christmas 2014 prior to coming up here and I used a 20w/60, again with no difference. I'm going to go back to a 15w/50 as it's basically what I should be using and will give me the best indication of what is happening.

I rebuilt the swivel housings and front bearings in 2012 and completed all oils at that point.

One thing I have done that hasn't been mentioned is I retrofitted a VW alternator in late November. The original 65 amper couldn't deal with life and more often than not, would leave me with a dead flat aux battery and I would have to turn the AC off the keep a decent speed. And that was only with a Engel fridge running on a long trip. The new one has the ability to run 140amps and basically slotted straight in. It has made the car perkier and stabilised the the fuel economy.

I have recently purchased all the parts to carry out a complete service including wheel bearings, trans, diffs, TC, swivel housing and all that good stuff. Will replace coolant and probably pull the radiator out for a proper flush and clean. I also have a few sensors to replace that I have found to be on the limit of ranges.

I think it would be wishful to think i can get it back to where it used to be, but if I can improve it, il be happy..

Just wish I had 12k to drop a 3.6 v8 diesel in.. That would solve most issues.



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I did notice that tyre pressure made a noticeable difference to both of mine. I generally run 31F/36R unladen as I have to drive dirt/gravel roads daily. Higher pressures and I tend to get stones drilling into the tyres. If I run 35F/42R, both can and will see a noticeable increase in economy.


I also usually run Penrite 20w/60, but was thinking of dropping back to 10w/40 this winter and see if there is any difference.


One thing I did to the Disco, that I believe has hurt economy, is switch from the std exhaust to a 2 1/4" one with smaller front muffler/hotdog rear. Sounds better, but feels it may have lost a little down low.