38 replies to this topic

[blue flash]

i can see your point,but this loss of mpg has only started since it had a service.

[Pitmonster]

In cold weather the car will pump in more fuel to compensate for the denser colder air.
In the summer I can get 500 miles to a tank but in winter it drops by about 40-50 miles.

I'm seeing the same results, and it was the same last winter

[FOCA]

In cold weather the car will pump in more fuel to compensate for the denser colder air.
In the summer I can get 500 miles to a tank but in winter it drops by about 40-50 miles.

You are only assuming the denser colder air is the reason for the drop in MPG, it may be insignificant and the reason for the loss of mpg in the winter is the winter diesel we are supplied (with antifreeze added), or the fact modern diesels take so long to warm up in the winter (and don't return a good MPG untill they are warmed up) the last point is the most likely cause (or it may be because of several reasons working together)

[blue flash]

so assuming foca that your right (im not saying your wrong)would that account for me losing about 15 mpg.

[FOCA]

so assuming foca that your right (im not saying your wrong)would that account for me losing about 15 mpg.

I don't think so, in my experience these things only make a few MPG difference (say 5mpg?/ 10%) and would not make as much as 15MPG difference, if it is correct mabee there is something wrong and the garage has caused your loss of MPG in some way?

[james_60]

Hi Folks

Just my pennys worth

Did they adjust the handbrake.

If the shoes are unevenly worn and it isnt balanced it could be partially on, on one side.

Check how hot your drums are after a 10 mile run. be carefull because they could be red hot

Jamie

[blue flash]

No james all the wheels and brakes are fine.sorry to keep ranting on,but just bin on a 30 mile trip,and i'm sitting in the car.37.7mpg was on the dash and within 45 seconds it had gone down to 34.2mpg.now,i'm starting to think this has to be electrics.any ideas.

[Pitmonster]

Have you done an actual calculation yet, or is this all based on trip computer numbers?

[james_60]

If this is based on the trip computer which i think it is then its not a correct value

Only A Brim to Brim result will give an accurate figure.

That is why i use Spritmonitor.de (see my mpg figure)

Its low because i have a lead foot (not saying you have a lead foot)

Jamie

[blue flash]

no pitmonster it's done on the trip,my dad went into hospital sunday night and havent had the time to go for a tidy drive.hoping to do it some time this week.

[Pitmonster]

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

[blue flash]

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..

[Pitmonster]

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

[cragger89]

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.

[Pitmonster]

"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.