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Discussion Starter · #1 ·
Hi all.

My 2009 BMW 318d has been returning very poor MPG for the past while. It recently had a full service but this made no difference.

Last week on a 200 mile motorway journey it only returned 42 mpg. I generally keep the speed at 120-130 kph. Via the hidden menu I noticed that the engine temp was 80 - 83 degrees C.

Is this temp too low? Would it be enough to cause 42 mpg?
 

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at what rpm is the needle sitting at when at 120-130 km/h?

when you say full service was the fuel filter and air filter definitely changed?

is the temperature that you were reading water temperature or engine oil temperature? (prob makes no difference anyway, surely water, oil would be probably hotter)
 

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I'm a 2 wheel man really
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I had a similar issue with my E46 320cd '05. Changed the main thermostat and EGR thermostat. Car now stays at a constant temp whether summer or winter. My MPG returned to normal too
 

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Discussion Starter · #18 ·
at what rpm is the needle sitting at when at 120-130 km/h?

when you say full service was the fuel filter and air filter definitely changed?

is the temperature that you were reading water temperature or engine oil temperature? (prob makes no difference anyway, surely water, oil would be probably hotter)
RPM about 2.5K I think and its a 6 speed manual gearbox.
Fuel and air filters were changed ok.
Temp was option 07.00 in the menu's. I think this is the coolant temp.
 

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I've driven three e46 320cd's for the last 4 years and I find that in the winter I get 480 - 520 miles to a tank and in the summer I get 560 - 600 miles to a tank.
this could be right , I see the same with the van, might be the additive they put into the diesel for the winter
 

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Discussion Starter · #20 ·
Update:

I got a diagnostics check done and was told the coolant temp sensor was reading negative (-40 degrees F)

Could this be causing the reduced MPG?
Need a new sensor or could it be a connection / wiring issue?
 
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