Improving the MPG on my manual 300tdi 1996 discovery.
After having a couple of disco's now, mostly then selling them becuase work meant I had more miles to do so a car was needed, I decided enough was enough and that despite having size, weight and barn door mechanics not on its side, the trust 300 tdi disco manual had a few secrets up its sleeve to achieve a more car like mpg.

I know the purest's will say a 4x4 is not about mpg and I would totally agree.
But the fact of the matter is, we love our old barge's and better mpg is going to be better for the pocket and as such a better reason to keep them?!

My findings;

Base 1996 disco 300 tdi manual. 140k, no mechanical issues (known), completely standard to start with, no roof racks or lifts etc, std 40/60 split offroad/road tyres at correct pressure.

Average over a month doing 36 miles a day on the same A roads at a steady 55-60 mph where possible, 6 days a week. 31 mpg tank fill confirmation.

1) Decat, Mid box removed, Snorkel, egr delete and silicone hoses... the usual stuff we do! 33mpg

2) Full service in fully synthetic 10w40 oil, zx1 treatment (who knows if this stuff works but I always chuck it in) millers ecotech, diff/gear/transfer box oils replaced with FS where possible. 34mpg

3)Remove viscus fan, made no difference in my case because the coupling was working as it should with no demand on the engine when it was cool, so I left it fitted.

4) Remove injectors, ultrasonic clean, new nozzles and pop balanced by a local company. 39 mpg!

5) Turbo removed, cold side cleaned, polished and finished with autosol for as smooth a finish as I could get. Outlet opened up slighlty, inlet opened up slightly more.
Hot side de-coked as best I could. Waste gate checked for free movement and operation, gate checked for seating etc.
No improvement in mpg but turbo started to build pressure about 250rpm earlier. Engine seemed slightly more willing on hills. If I am honest this could be down to polishing and opening up the cold side, or just cleaning it in general.

I am pretty sure that with a larger IC and few well thought out tweaks to the fuel pump and boost, along with re-locating the boost signal pipe to the inlet manifold, I should see over 40mpg repeatable.


Just thought I would share what I have found.

Its interesting how the injectors get over looked as the main culprit for mpg loss. Its easy to forget that just because the injector nozzles are clean, doesn't mean to say that the injector pattern hasn't been eroded by the constant high pressure diesel over the years. Poor spray pattern (especially when the pistons contain the swirl chambers to mix the fuel with the air for max mpg and power), means the diesel doesn't get mixed with the air properly, droplets form, which causes smoke/incomplete burn etc.

I have also found out that the extra urban figure of 37mpg from new by land rover for the 5 door discovery 300tdi is taken at a constant 75mph. So needless to say at 55-60 mpg should be slightly better.

"MODEL URBAN EXTRA-URBAN COMBINED
mpg l/100km mpg l/100km mpg l/100km
Petrol models:
2.0 Mpi Manual 17.4 16.2 29.3 9.6 23.4 12.1
3.9 V8 Manual 11.9 23.7 23.4 12.0 17.3 16.4
3.9 V8 Auto 12.4 22.8 22.4 12.6 17.3 16.3
Diesel models:
300 Tdi Manual 24.9 11.3 37.5 7.5 31.6 8.9
300 Tdi Auto 21.7 13.0 35.0 8.1 28.5 9.9
Urban cycle
The urban test cycle is carried out from a cold start and consists of a series of accelerations,
decelerations and periods of steady speed driving and engine idling. The maximum speed attained
during the test is 31 mph (50 km/h), with an average speed of 12 mph (19 km/h).
Extra-urban cycle
The extra-urban test cycle is carried out immediately after the urban test. Approximately half the
test comprises steady speed driving, while the remainder consists of a series of accelerations,
decelerations and engine idling. The maximum test speed is 75 mph (120 km/h) and the average
speed 39 mph (63 km/h). The test is carried out over a distance of 4.3 miles (7 km).
Combined
The combined figure is an average of the urban and the extra-urban test cycle results, which has
been weighted to take account of the different distances covered during the two tests.
NOTE:
These figures should not be compared with the figures produced using the ECE/EEC
procedure previously required by The Passenger Car Fuel Consumption Order 1983. Because of
the changes in test procedure, even the urban figures would differ if the same car were subjected
to both tests"

I am now getting 39mpg week on week on my run to work and back from my disco.

Try a tin of diesel rhino done it to my 2.4 T4 vw get 4mpg extra now
only mods to engine are a decat k&n panel filter and timing set spot on

Power to weight is very often overlooked as well as aerodynamics.
If you don't need all 7 seats get rid of the other 5, got a snorkel or loads of extra lights that are like a parachute at speed? Heavy duty bumpers are not necessary if its a road vehicle. Tyres make a massive difference to mpg so maybe change to a narrower more road based design.

Very interesting read, thanks

how much has it cost to sort it all out though and has it made it worth the cost by the mpg saving?

I am looking at getting my injectors looked at though. how much did it cost for the 4 to be sorted?

Morning!

The injectors cost £200 for all 4 to be cleaned and pop balanced. I the nozzles cost £100. So £300 needs to be recovered on mpg saving. Which with the miles I do wont be long at all.
It is very worth it. Your injectors could be spotless clean but if they spray pattern is poor you will loose mpg and performance. It has made my engine a bit quieter, a lot more responsive and less inclined to die on hills and o cant complain with 39 mpg from a 2.5 ton house brick!

You can rebuild the injectors yourself, they are very easy to do if you are methodical. But pop balancing has to be done on a machine so with tome constraints and work i decided to pay out.

Funnily enough i bought a Disco for the mpg.

I do about 100miles a day to work and back, 6days a week. Most of it motorway with some country roads and town driving.

I was using my MG ZR but that was costing me £180 a week to use. Especially with all the gear i have to put in the boot aswel. So in my eyes. I'm already saving on mpg.

They are actually quiet efficient engines. They are even better with a vnt turbo

I do think it has quite a lot to do with the way you drive aswel. I have done 402miles to £80. Not had the time to work out mpg. But i think it ot alot better then the MG. And 100mile of that was towing a7.5 horse box that had **** it's gear box.

Good findings. Wouldn't it have been cheaper to buy new injectors though? Last time I looked they were about 45/50 quid each for standard ones.

Thank you for a very interesting and informative article Mudron... I have just MOT'd and put my 1996 Discovery 300TDI ES. 5 door 7 seater back on the road. I am regularly travelling from North Wales to Newbury (220 miles each way) to visit my lady friend, and am fairly pleased to record a true tankful to tankful MPG of 34 mpg @ 65 - 68 mph... The previous owner a race garage who used it as a tow barge, have disconnected the EGR, tweaked the pump, and supplied me with a new de- cat front pipe, yet to be fitted... also new shocks all round and suspension bushes ect were replaced making this older Land Rover a pretty quick and well handling motor.... wiper blades and No plate light bulbs were all that were needed for the recent MOT.

The injector overhaul sounds like a plan, but it is already an excellent starter, no smoke at all and a very smooth runner from cold.... I suppose I should trim 5mph of my average speed which would help the consumption, but this car is so willing it is a shame to hold it back...
Thanks again for your interesting posts Mudrom...

Alan.

I agree cost wise new ones would be a bit cheaper. I hadn't really checked the prices. Worn injectors dont tend to show up any starting or running symptoms unless they ate seriously out of spec. The pop balancing alone is worth the trouble, dont forget these are 2 stage injectors so need to be calibrated correctly.

Driving style does make a big difference. I have kept my driving style as consistent as possible.

There are other thing that will gain mpg such as head work, VNT and LPG. But its a case of how far do you go?

LPG is on the list of things to try next when funds permit.

I did dabble with the EDC ecu and a custom chip and replacement ecu from another make of car but the EDC ecu is very very basic and doesnt lend itself to different tuning options. The engine loom would require modification and sensors added to gain decent control. The best thing for edc is the 'Every' mod to gain slightly better mpg and alot more power.

I had 38 mpg on a run on shell v power diesel. Good thread thanks for the tips!

Any ideas if these changes will benefit a TD5?

I would have thought the above would apply to the td5. A remap would see slightly better mpg though.

August is my families busy month....school hols, visiting family, going on holiday to Devon and the Lakes etc. My Discos get loaded with canoes, camping gear and 400 electronic gadgets to keep the kids happy!
Last August I had a D1 300td1 auto, this August I had a D1 200tdi manual and did about the same mileage as last year, 2300 miles.
I reckon that the manual has saved me about £80 for August....
This is a guestimate.... but when driving the auto I always had one eye on the fuel gauge, where as with the auto I hardly give it a second thought!

I have found on ordinary roads a manual is more economical, but if you can get an EDC auto on the motorway and hold a steady 55-60mph it will produce a very good mpg. It is the torque converter that saps the mpg in ordinary use. I guess an EDC 300 with a manual box would be best of all.