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Loss Of Mpg.

39 posts in this topic

I filled up on Sunday and my trip was 13% out from the actual (calculated) MPG

In the last few weeks it was 10% out, and in summer it was 1% out

Clearly the cold weather makes the trip computer less accurate, and its getting worse as it gets colder

I would suggest that a big part of what you're seeing is inaccurate info.

Yes there will be a reduction in MPG because of the cold, but it won't be anywhere as bad as you're thinking - because your car is telling you porkie pies.

To get an accurate calculation you need to fill to the brim, zero your trip (mileage), drive til the light comes on (450-500 miles), and refill to the brim again. Then do the maths based on miles traveled and litres used (from the fuel pump)

It's the only way to truly know. Shorter distances don't give accurate info and can be very misleading.

If you have a smartphone there's plenty of apps that will do the maths for you

Ps hope your Dad 's ok

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re the contuing sage of my loss of mpg.my dad's ok pitmonster,(thanks for asking)bit of a heart problem,should be out friday or sat.anyway this morn my mrs's car read -3c on her car focus 1.6 diesel 2012 on mine it read 0c and when the car is warmed up the temp needle pointing to normal (12 o clock position),if it throttle it hard it needle goes back to (10 o clock position) then it goes back to normal.it defo has to be electrics now,anyone with idea of what it could be..

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Your temp gauge shows the temp of the water in your cooling system, not the temp of the engine itself.

The water temp will go up and down due to:

* Thermostat opening and closing

* Cooling fan (on the radiator) starting and stopping

This is normal behaviour and is nothing to worry about

As you rev the engine it's entirely possible that the engine reacts by switching on the cooling fan - in anticipation of the extra heat generated by the engine revs - and so the water temp drops.

This may even be a proactive thing controlled by the ECU : better to start cooling the water before it starts to get too hot, not after

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After reading this, honestly, take it back to the garage you had it serviced by.

The coolant temperature needle should ALWAYS stay rigid at the 12 o'clock position unless there is a fault. My Audi A3 wasn't heating up due to the thermostat always being open. This meant that sat still, it would reach "90 degrees", but the moment you drove it, it cooled down quickly. This affected MPG in the way you are describing - the engine was never staying at the proper temperature (or even reaching it, in my case) so the ECU was adding more fuel to the mixture, meaning it was running rich.

It could be sheer coincidence if a thermostat has failed (or stated to fail, I don't know if they can start to break slowly or not.) But it wasn't doing this before, either that, or the cold weather has made a long fault suddenly become noticable.

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"The coolant temperature needle should ALWAYS stay rigid at the 12 o'clock position unless there is a fault."

With respect, the water temperature will rise and fall under totally normal circumstances.

Temp goes up, fan goes on, temp comes down, fan turns off, temp goes up, fan goes on, temp comes down, fan turns off...

This can cause the gauge to fluctuate from 1/4 to 1/2, and back to 1/4, and back to 1/2, and so on, but its perfectly normal.

You only have to worry if it goes way above 3/4 or into the red.

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this morn my mrs's car read -3c on her car focus 1.6 diesel 2012 on mine it read 0c and when the car is warmed up the temp needle pointing to normal (12 o clock position),if it throttle it hard it needle goes back to (10 o clock position) then it goes back to normal.it defo has to be electrics now,anyone with idea of what it could be..

So you're assuming there is a problem that is causing low MPG?

It could be that your computer is wildly innaccurate, and you actually haven't lost much MPG (only that which is normal in winter). I wouldn't bother doing anything until you measure again with a manual fill up. I normally get low 50's in summer, but recently i've been getting very high 40's. However the trip used to be 0.1-0.2mpg out, but now it's showing 44mpg. Others have reported this problem as well.

Don't assume that your car has a major problem just because an innaccurate dashboard display says you do!

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Respect accepted and I know that the temperature will change all the time, but the needle in general practice shouldn't move (unless there is a fault) - the only time I've seen the temperature needle drop even on a cold day is when I had a thermostat problem.

The temperature gauges doesn't normally even give a roughly accurate reading - it will just go in the middle once it is within the threshold of being at a normal temperature.

You are correct in saying it is only a real worry if it goes in to the red, but if it isn't running at full temperature, it is still a fault which should be resolved. I may not be correct, it's just something else the OP can look in to if he wants to.

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right men,have been doing some looking about on the net for the past 2 hours,what do you all think about the water temp sensor is faulty.i've read that this sensor water works the fuel mixture as well...

i also would like to thank you all for your answers and hopefully will sought something out soon,cheers Brian.....

it's only what i've read

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ok,done the filling the fuel tank,used it all ? then filled it back up again.now acording to the caculations im useing 3 gallans less to a tankfull then what the gauge is showing me.any one have an idea of what could be faulty.gauge itself,gauge in the tank or any thing else,cheers for any answers.

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What engine oil exactly did you use exactly? you just mentioned Eurocarparts. was it the A1 type that ford recommend?

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the focus needle on the temp gauge will indeed move from the 12 0 clock position as the engine gets up to the point where the thermostat opens and allows coolant through the radiator the pretty cold air will cool it way too much the temp needle drops and the thermostat closes its pretty simple if the gauge never budges ide be concerned having had a few fords not one in the winter has stayed solid in the middle till the engine has had a chance to fully warm up ie more than a 20 mile drive at temps below 6 degrees

it will rise than fall then the thermostat closes and it will rise and likely stay there the thermostat was changed via odb on later focis to show a constant temp even when its not at 90 degrees after lots of people went to ford complaining so from around 80 degrees on the later focis the gaiuge actually shows 90 degrees my gauge shows just below 90 however ford tested it and used laser thermometers and it was 90 degrees the gauge nor the sensor or thermostat was faulty other ti vct owners have had the same issue 3mpg is not that much of a difference to be honest even over a full tank and i dont think its anything to worry about the computer isnt accurate its a general ball park figure as is the temp gauge only the fuel gauge is really accurate

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ok,done the filling the fuel tank,used it all ? then filled it back up again.now acording to the caculations im useing 3 gallans less to a tankfull then what the gauge is showing me.any one have an idea of what could be faulty.gauge itself,gauge in the tank or any thing else,cheers for any answers.

The gauge is not accurate, they are "hit or miss" the tank also has a void in the top to allow for expansion, which can fill with fuel - ive got a big write up somewhere about it but can't find it, if i do i will pass it on

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i just used the europarts own 5w/30 semi oil,cant remember what,bottles goin in the bin.ok thanks foca.

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ok thanks to artscot 79.it's nice to know the motors not going blow up or worse.

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