New MG ZS high fuel consumption and frosty glass shattering

michaels

9-10mph average speed sounds about normal to me.  I also suspect that on short journeys the engine does not warm up and so possibly runs in a low efficiency warm up mode.

WE had a mid size petrol car and on our usage pattern (lots of short journeys form cold in traffic) we got less than 20mpg.  We switched to the diesel of the same car and got low-mid 30s mpg - but loads of reliability issues DPF, EVR and even turbo runaway because it never ran a complete decarbon cycle.  Both also seemed to have very short clutch life (we did more gear changes in 1000 miles than a motorway car would do in 50,000.

Buying an electric car has solved all these problems.

Goudy

Modern fuel injected cars tend to enrich their fuel mixture at start up for only a very short time.
The coolant might take some time to warm up but the fueling will trip into a normal running cycle pretty quickly even from stone cold.

The fueling has two basic strategies. Open and Closed Loops.

The Open Loop is it's strategy when starting (or when something goes wrong like a sensor, as rich mix is often safer to the engine than a lean mix).
It's a preset rich fuel mix to get the engine going from cold. The ECU isn't taking any signals from the O2 sensor to adjust the fueling at this point.

The Closed Loop is a feedback loop which is constantly adjusted.
The temps of the exhaust gas are monitored by the O2 sensor and the fueling is adjusted based on the results of that.
Hot gas and the mix is lean, so it adds fuel.
Cooler gas and the mix is rich, so it takes fuel away.

The ECU knocks the fueling back and forth to try and get a near perfect fuel trim over it's long term fuel trim, which is close to 14 parts air to 1 part fuel.
(O2's turn heat to voltage so it's switch will be between something like 0.9v to 0.1v, so long term trim should be around 4.5v)
To do this though the O2 sensor needs to be hot to get a reliable signal.

Modern O2 sensors are fitted with heaters inside them which has made the change from Open to Closed Loop much much faster and long before your temp gauge starts to creep up.

Older fuel systems without heated O2 sensors worked differently and took longer to drop out of it's enrichment cycle as it's signal to change was usually from the coolant system which took much longer to warm up.

Before that were carburettors which either used a manual enrichment  or choke setting or an automated system that was again usually linked to the coolant or surface temp of the engine/carb.

A modern fuel injected car will only take a few moments to detect the O2 sensor is at operating temp and switch out of it's Open Loop enrichment setting.
Turn the ignition on on a hot engined car and it will more often than not detect the O2 is hot enough to run directly in Closed Loop from the off.

The reason for the bad fuel economy is just the fact this car is constantly accelerating which is when it's most inefficient.
All it is doing is speeding up from a standstill and stopping, over and over again.
It is hardly ever getting to the point where is can sustain it's speed and run more efficiently.

ComicGeek

To be honest, even that type of journey isn't overly efficient in an electric car. I crawled through London a few weeks ago, and got nearly half the efficiency I would do in free moving traffic - it's takes a lot to accelerate a heavy EV from stationary, and braking doesn't reclaim all energy. You really need to be at coasting speed to get the most from the EV.

But at least there's less to go wrong!

Herzlos

It's presumably better in an EV than an ICE though, as the EV should be reclaiming some of the braking energy to recharge whereas on an ICE it's wasted, and isn't using any power to idle. But yeah, stop/start traffic sucks for everything.

Stubod

Would be interesting to see the mpg results when the OP takes the car out for a "normal" drive, ie 10+ miles on congestion free roads and "cruising" around 45-50 mpg? If the mpg is still pants it suggests there is a problem with the car, if the mpg is around the published figures (45mpg) then all is well??

tifo

Stubod said:

Would be interesting to see the mpg results when the OP takes the car out for a "normal" drive, ie 10+ miles on congestion free roads and "cruising" around 45-50 mpg? If the mpg is still pants it suggests there is a problem with the car, if the mpg is around the published figures (45mpg) then all is well??

10+ miles on 45-50 mph i get mpg in the late 20s. Motorway for an hour or more i get mid to late 30s. Never have I got 46-50mpg on the motorway and that was with over 2 hours constant motorway driving ..... At the mpg I get I dare not take it further.

As an example, manchester airport is about 40 miles from me, last time i went it used £30 of fuel on the return journey. I know it's not constant motorway 70 mph but a lot of it was over 50 mph.

tifo

[Deleted User] said:

Clearly, the OP does incredibly slow journeys with massive amounts of engine idle time, I don't think any car would get much better economy.

Nope, I do shorter journeys and never leave my car on idle unless it's in the morning for maybe a few mins before driving off.

tifo

MG say they give no mpg guarantee (from their specified figures) as it's all down to 'driving style'. That's like car insurers telling everyone 'it's your postcode' for higher premiums (my insurance is high due to various factors, such as postcode and ethnicity).

tifo

Deleted_User said:

its a terrible brand to buy , why did you choose this out of all the options?

I don't know now, wanted a cheap car for a short while and the 0% apr did it.

tifo

lordmountararat said:

As already mentioned, check that the computer is not set for US gallons. US gallons are approx 20% smaller than imperial gallons. (3.78 litres to a US gallon; 4.54 litres to a UK  gallon).

I calculate the mpg from the amount of fuel put in, from the money paid. It's definitely not on US gallons as my figure is usually a half mile to 1 mile less mpg than shown.