Poor MPG

[.....]

Ok I'm looking for some ideas as to why my mpg has gone down.

Motorway driving at 70/75 mph the car will only return just over 44 to the gallon.
It used to give more than that.

The car is a diesel manual with the 160 map on it done by Brian.
The engine has had a tetra clean treatment. The oil has just been changed along with the crankcase breather filter.
It's also had new vitron O rings fitted I got from Jules.
It has an ERG bypass fitted and an inline thermostat fitted ( engine temp measured at 87 degrees on the T4 session)
The car has only done 94 k

When I noticed this a few weeks ago I took the car to Rich and he put it on his T4 which confirmed the Maf sensor was fine but said two of the injectors were iffy. I have had both of these injectors refurbished and although the car runs smoother it has made no difference to the mpg.

I've just come up from London and over a 300 mile round trip (nearly all motorway) the car has still only returned 44.1 mpg.

Has anyone got any ideas whats causing the poor mpg?

[James.uk]

44 mpg from a car the size of yours is very good. :}

I know we get a lot of tales about mpg but if you can get over 40 mpg out of the huge cars we drive then you are doing very very well. ;)

How did you determine your mpg? if it was via calculating it via the brim to brim system, then it will be pretty accurate. Any other system will be iffy.. :shrug:
...

[.....]

I confirmed the mpg by brim to brim on 2 separate occasions.

I used to get just over 50 mpg doing long trips. I don't drive the car fast or rev it much. In fact I get nearly 40 mpg out of my works van and that weighs 2.8 tons!

[Jim W]

Check turbo hose for splits or holes also check O rings have seated properly the bottom one has a tendancy to pinch on fitting also check all air seals are tight

[.....]

Check turbo hose for splits or holes also check O rings have seated properly the bottom one has a tendancy to pinch on fitting also check all air seals are tight

Turbo hose was replaced last year and mpg was good up to about 6 weeks ago. I fitted the O rings in November so it would be very unlikely that they could be causing a problem now. Also I did it with the bumper off so I know they went in properly.

[.....]

Im wondering if it could be something to do with the tetraclean although in theory that should improve the mpg. After I had it done the car wasn't usd for 5 weeks. It was after that that I noticed the drop in MPG.:shrug:

[Doc Evil]

Have you changed the air filter and fuel filter it might be breathing like an athsmatic kitten
Also are your tyre pressures correct and in this hot weather are you drivig with window open
Doc

[.....]

you don't open widows.... that lets the outside in.
Check tyre pressures each week.
Air filter is fairly new.

[minty2]

I'd be inclined to carry out a full inspection of the intercooler. Look for holes in the plastic end pieces and the main body matrix. I had poor MPG and low power before discovering a gaping hole! A second hand refurb off a fleabay dealer fixed both. Turbo hose was replaced last year and mpg was good up to about 6 weeks ago. I fitted the O rings in November so it would be very unlikely that they could be causing a problem now. Also I did it with the bumper off so I know they went in properly.

[.....]

I'd be inclined to carry out a full inspection of the intercooler. Look for holes in the plastic end pieces and the main body matrix. I had poor MPG and low power before discovering a gaping hole! A second hand refurb off a fleabay dealer fixed both.

the car has bags of power...:shrug:

[albert81]

There's no reason to be worried about anything. ........after all u get 44mpg.

[.....]

There's no reason to be worried about anything. ........after all u get 44mpg.

but I was getting more...hummm

[Avulon]

Have you run the on-board diagnostics temperature monitor? maybe it's not getting up to temp. Plenty of info on diesel thermostats and running temperature and relationship with mpg on the forum.

[vindaloo]

I wish my diesel delivered 44mpg.

[.....]

Have you run the on-board diagnostics temperature monitor? maybe it's not getting up to temp. Plenty of info on diesel thermostats and running temperature and relationship with mpg on the forum.

See first post!:duh::getmecoat:

[Avulon]

See first post!:duh::getmecoat:

I did. Of course I did make a natural assumption that the car wasn't bowling down the road at 70mph when that reading was taken, I could be wrong...:D

87 on the T4 with the car standing still is quite different to rolling down the motorway with a 70mph breeze through the radiator. Unless the fan is running the radiator will do very little to cool a stationary vehicle unless it's angled to let some convection to take place. My question was aimed at evaluating the performance of the thermostat. A premature opening thermostat or one stuck open will have little to no cooling effect unless the car is moving.

[Doc Evil]

There could be many contributory factors as to why your not getting same MPG will list a few take your pick
wear in the sensors (as they get older their performance dan deteriorate )
Different fuel (even from same garage it can be different from time to time depends on where its refined)
Weather conditions (head winds placing extra drag on car or very hot air can have detrimental affect on combustion efficiency)
Driving conditions (idiots pulling out in front of you or having to accelerate more often even gently will use more fuel than coasting or constant speed)
Brakes binding slightly (a sticky piston can play havoc with your MPG)
Aircon issues if used
Extra electrical load (it all has a detrimental affect)
Dirty car (if airliners quote it as an issue why not us) lol
I'm sure others could add to this list of things that may have had a cumulative affect



Doc

::shrug:cool:

[polinsteve]

I blame **** modern derv. We had 3 diesel 75s in the family and all achieved close on 50mpg on a run. Since the advent of "cleaner" diesel I get about the same as you. The only way I can achieve 47-48 mpg is to keep the speed down to 60-65 mph and that is not usually an option I care to choose.

[clf]

Ok I'm looking for some ideas as to why my mpg has gone down.

Motorway driving at 70/75 mph the car will only return just over 44 to the gallon.
It used to give more than that.

The car is a diesel manual with the 160 map on it done by Brian.
The engine has had a tetra clean treatment. The oil has just been changed along with the crankcase breather filter.
It's also had new vitron O rings fitted I got from Jules.
It has an ERG bypass fitted and an inline thermostat fitted ( engine temp measured at 87 degrees on the T4 session)
The car has only done 94 k

When I noticed this a few weeks ago I took the car to Rich and he put it on his T4 which confirmed the Maf sensor was fine but said two of the injectors were iffy. I have had both of these injectors refurbished and although the car runs smoother it has made no difference to the mpg.

I've just come up from London and over a 300 mile round trip (nearly all motorway) the car has still only returned 44.1 mpg.

Has anyone got any ideas whats causing the poor mpg?
How much more than 44 mpg are we talking about? It would be realistic to see a drop of 3-5mpg with air con on. Similar with tyres slightly low.