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charcoal

Member Since: 28 Jul 2014
Location: Hampshire
Posts: 941

Sudden drop in fuel mileage

Usually I would get 30-31mpg from the Defender which is mostly motorway and A road driving on the commute to work. Recently that has dropped suddenly to 28 last time I calculated and seems to be even lower now, I haven't yet filled up to work it out but where I would once get 450-470 miles from a tank I'm now sitting at about 400 with the low fuel light now illuminated. The only things I've changed are installed cruise control and adding half a litre of engine oil as it was a little low. Surely using cruise control should do the exact opposite of this?

1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold
1995 Land Rover Defender 110 V8 Station Wagon ~ Sold

1985 Land Rover 110 ex mod project Tithonus ~ Sold

23rd Sep 2023 9:44pm

landy andy

Member Since: 15 Feb 2009
Location: Ware, Herts
Posts: 5423

2006 Defender 110 Td5 USW Zermatt Silver

Check your fuel pressure regulator on the cylinder head. Often leak.

23rd Sep 2023 9:48pm

charcoal

Member Since: 28 Jul 2014
Location: Hampshire
Posts: 941

Thanks will take a look tomorrow, is this something that has to be replaced outright when leaking or will a new gasket suffice? 1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold
1995 Land Rover Defender 110 V8 Station Wagon ~ Sold

1985 Land Rover 110 ex mod project Tithonus ~ Sold

23rd Sep 2023 9:59pm

Steve B

Member Since: 22 May 2009
Location: Warwickshire
Posts: 586

Most likely the weather.

Unless there is a pool of fuel underneath or the oil level is increasing (injector seals or cracked head) I would not worry.

My golf GTD has also lost MPG since yhe recent hot weather.

24th Sep 2023 12:13am

charcoal

Member Since: 28 Jul 2014
Location: Hampshire
Posts: 941

Are you sure? I have been driving it daily throughout the hot weather and its still been returning 30mpg up until the week before last 1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold
1995 Land Rover Defender 110 V8 Station Wagon ~ Sold

1985 Land Rover 110 ex mod project Tithonus ~ Sold

24th Sep 2023 12:42pm

markb110

Member Since: 22 May 2010
Location: Guildford
Posts: 2522

Shrinkflation…….they’re probably mixing it with water…..

24th Sep 2023 1:19pm

diesel_jim

Member Since: 13 Oct 2008
Location: hiding
Posts: 6037

Check the MAF sensor as well, especially if you've noticed that performance has dropped off a little.

24th Sep 2023 5:39pm

Steve B

Member Since: 22 May 2009
Location: Warwickshire
Posts: 586

charcoal wrote:
Are you sure? I have been driving it daily throughout the hot weather and its still been returning 30mpg up until the week before last

No not sure, an observation after driving diesels. The weather has cooled off a little especially in the mornings.

Try not using the cruise control and see If the mpg recovers, I think you can drive better without it.

25th Sep 2023 10:42am

charcoal

Member Since: 28 Jul 2014
Location: Hampshire
Posts: 941

I gone through a few of the points made here, MAP sensor was a little oily so cleaned that, tried driving with MAF plugged in and unplugged and felt no difference in performance with either of these. Fuel pressure regulator doesn't appear to be leaking. I did notice however that the egr valve actuator is absolutely caked in filth, maybe if this is no longer working correctly it's contributing to the loss of mileage? 1999 Land Rover Defender 110 td5 station wagon
1998 Land Rover Defender 110 County Station Wagon ~ Sold
1995 Land Rover Defender 110 V8 Station Wagon ~ Sold

1985 Land Rover 110 ex mod project Tithonus ~ Sold

28th Sep 2023 5:47pm

Hazza

Member Since: 10 Jan 2011
Location: North Yorkshire / Leeds
Posts: 208

If you don't notice any difference with MAF plugged in or unplugged I'd suggest getting it replaced with a VDO or Siemens one (or better, find someone with a nanocom to test it with). 1990 Defender 110 200TDI Camper - now converted to Td5 power

28th Sep 2023 8:52pm

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