w220 high fuel consumption

jplpt

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Porto, Portugal
Your Mercedes
w220/1999/S320cdi
I have been getting fuel consumption in the low 20´s mpg in my w220 s320 cdi.
What is wrong?
What can i check/ do?
 

Oarsman

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Norfolk
Your Mercedes
W221 S350L CDI Bluetec, Range Rover Vogue SE 4.4 TDI, 1963 Triumph TR4
What temp is showing on the guage?
 

Craiglxviii

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970 Panamera Turbo; W221 S500L AMG Line, C215 CL500, W251 R350L AMG Line, plus several more now gone

Oarsman

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W221 S350L CDI Bluetec, Range Rover Vogue SE 4.4 TDI, 1963 Triumph TR4
Change of thermostat would help. Should be running a 90c when up to temp.
Used to get mid to high 40s with myW220 on a run.
 

Paul1948

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Bournemouth
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S320 CDI 2003
Agree with your figure for around town, same as mine but on a run motorway 30 plus miles temperature sits at 90 and mpg goes to 42-45 @ average 60mph.....need to replace your thermostat.
good luck
 

range rover

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Northern Ireland
Your Mercedes
E Class Blue EFFICIENCY 250 CDI Sport 2013
I never get over 41mpg, having said that it was fitted with a Brabus chip which for some reason or other caused 'hunting' intermittently, obviously a fault with the chip since it is now removed and the car runs perfectly. It has over the past 7k miles returned an average of 33.4mpg. I wonder if it would be a good idea to have it hooked up to 'star' as previously the chip was fitted when it was last on the computer.
When I got 41mpg it was on a trip of about 220 miles, the more usual short distances record 28-30, starting from cold I have seen 9.5! And of course the summer weather shows an improvement.
 

Roger Willatt

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Sep 29, 2017
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Barton on Sea
Your Mercedes
S-Class 2005 320CDi
Just bought this 2005 S320CDi which has averaged 39.3mpg over its entire life and 26,000m. I am averaging 38mpg over mixed motorway and town driving. My previous 2003 S320CDi used to manage 52mpg on a long motorway drive cruising at 120km/h, it had smaller wheels and narrower tyres which I think made a big difference to the economy. D8A73DBC-A1AF-48DA-AE06-8E82BD1832F6.jpeg
 

umblecumbuz

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Wales and Gozo
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S204 and CLC 204 cdi, MX5, Kia Soul
This thread is a few months old, and you've probably sorted your problem by now. But ... the thermostat has been suggested as the culprit. Before deciding to change a 'stat, it's worth checking it carefully.

For instance, is it actually showing 80degs or less when the car has warmed up, or is it closer to 85?
More significantly when checking a suspect 'stat, does this temperature remain constant during a mixed journey, or does it fluctuate? In stop start traffic, does the temperature rise, only to lower when you get a period of uninterrupted cruising?

If your engine temperature fuctuates, then change the 'stat - it's faulty and will give you poor fuel consumption. If it's steady at 85, then forget the 'stat - the fault lies elsewhere.
 

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