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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
Why has my MPG dropped so much?
Hi all, need some help in working out the cause of a problem.

5 months ago i was getting 29 MPG routinely from my 300tdi 110 in daily runs (that was after fuel system revamp - new injectors, recondition injection pump, new turbo fitted) and emissions were as per a new saloon car, ie virtually nil. i always fill at the same garage and i've checked the accuracy of their pump meter. For the last few months I've been getting 25 - 26.5 mpg. The only things that have changed are new half shafts and wheel flanges - nothing extra bolted on. Emissions remain almost nil.

i'm pretty ignorant at how turbos and engines work, but since the injectors are clean and nothing is coming out in the smoke, and nothing is leaking (no traces where i park overnight) i can only think some fuel is disappearing in the turbo somehow.

can anyone shed any light on what might be going on? the difference in mpg is another 30 miles on a tank of fuel.

thanks in advance for your suggestions! 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #751911 17th Jan 2019 5:04pm
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grafty99



Member Since: 15 Aug 2012
Location: North Devon
Posts: 4796
United Kingdom 2002 Defender 90 Td5 HT Caledonian Blue
Has the injection pump timing been checked? 2002 90 Td5 Station Wagon
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Post #751913 17th Jan 2019 5:21pm
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Marks Landy



Member Since: 09 Feb 2015
Location: Cheshire
Posts: 302
United Kingdom 1985 Defender 90 200 Tdi SW Java Black
Might just be the winter diesel that’s in the pumps November to March.
I get a small MPG drop each winter.
Post #751922 17th Jan 2019 5:53pm
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yostumpy



Member Since: 01 Aug 2010
Location: n/kent
Posts: 327
https://www.pistonheads.com/gassing/topic....;t=1632376 'Volvo XC 70, taking the rough with the smooth’
Post #751930 17th Jan 2019 6:19pm
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richcl



Member Since: 25 Mar 2011
Location: tewkesbury
Posts: 25
United Kingdom 
Agree with above, winter diesel.

Would rather loose a bit of economy than have fuel waxing.
Post #751932 17th Jan 2019 6:23pm
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Retroanaconda



Member Since: 04 Jan 2012
Location: Scotland
Posts: 2706
Scotland 
Check your tyre pressures too.
Post #751934 17th Jan 2019 6:31pm
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Rashers



Member Since: 21 Jun 2015
Location: Norfolk
Posts: 3571
United Kingdom 2014 Defender 110 Puma 2.2 USW Corris Grey
Marks Landy wrote:
Might just be the winter diesel that’s in the pumps November to March.
I get a small MPG drop each winter.


Well, every day is a School day! Had no idea there was any difference, but it makes sense.

I have never checked the Defender's MPG.
Post #751942 17th Jan 2019 7:00pm
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Grouse



Member Since: 16 Apr 2012
Location: on the hill
Posts: 525
Just trying to think outside of the box, but, This doesn’t coincide with your change in air filter system by any chance ?
Post #752025 17th Jan 2019 10:39pm
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MadTom



Member Since: 10 Sep 2013
Location: Olomouc
Posts: 641
Czech Republic 1999 Defender 130 Td5 HCPU Baltic Blue
Possible an air leak somewhere between turbo and engine, loosing a bit of pressure made by turbo. "Drobek" = The Small One - Discovery 2, "Blufínek" = The Blue Thing - Defender 130, and for me at least Ford Mondeo Smile
Post #752050 18th Jan 2019 9:00am
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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
grafty99 wrote:
Has the injection pump timing been checked?


thanks I'll check 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #752055 18th Jan 2019 9:35am
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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
Marks Landy wrote:
Might just be the winter diesel that’s in the pumps November to March.
I get a small MPG drop each winter.


it started when the weather was still warm - shirt sleeves in Oct/Nov where i am so i don't think that is the cause. but i'll keep in mind, thanks. 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #752056 18th Jan 2019 9:37am
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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
Retroanaconda wrote:
Check your tyre pressures too.


checked weekly, religiously. so that's not it thanks. 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #752057 18th Jan 2019 9:38am
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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
Grouse wrote:
Just trying to think outside of the box, but, This doesn’t coincide with your change in air filter system by any chance ?


improving the air flow to the donaldson filter with a 3 inch tube all the way increased the mpg from 27-28 to 29 (and 30.5 on a long run) I have experimented with a forward facing air ram head and my donaldson topspin head on top of the RAI tube but surprisingly that made no difference at all. 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #752058 18th Jan 2019 9:41am
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Retroanaconda



Member Since: 04 Jan 2012
Location: Scotland
Posts: 2706
Scotland 
Winter diesel has a big impact on my Tdi. You can see the cyclical seasonal trend of MPG over a two-year period quite clearly here:


Click image to enlarge
Post #752059 18th Jan 2019 9:44am
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foxhound



Member Since: 02 Mar 2013
Location: United Kingdom
Posts: 363
United Kingdom 1995 Defender 110 300 Tdi SW Alpine White
MadTom wrote:
Possible an air leak somewhere between turbo and engine, loosing a bit of pressure made by turbo.


thanks for this

and thanks for the pistonheads winter fuel link yostumpy.

So far the injection pump timing and turbo air leak seem to be favourites - although having read up a bit on winter diesel it may be that it's not the actual temperature where I am that's the issue (and I use a rad muff to warm the engine), but the diesel mix the fuel companies sell. I'll ask my garage as it's the only place I full up at - their pump is accurate, I tested it and tested some big brands nearby and they were charging for more fuel than actually delivered! 110 Defender 300tdi & Penman trailer with ally exped top and roof tent
Post #752060 18th Jan 2019 9:47am
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