Displayed mpg is now low after starter motor replaced

[ACintertec]

Hello all, my second post - now after some advice...

I bought a 2004 X3 2.0d not long ago. It drives really nicely and i was pleasantly surprised by the fuel economy figures reported by the mpg readout on the dash. I've been in a Merc GLA180 courtesy car for the last 2 months and its mpg was terrible. The X3 reads around 27mpg on short around town journeys and will go up into the low to mid 30's if you are on A roads between towns (say 4 - 5 miles and only a few traffic stops) On the way back from Manchester recently, it was on 38mpg - I accidentally reset it on a long downhill, nearing home and it got to 42mpg) All good so far.

I had to have the starter motor replaced a few days ago - ever since then, the mpg figure stays in the low 20's, no matter how I drive. Its also taking longer to heat up - though the outside temp has dropped a little since the repair was done. is there anything wiring - wise or sensor - wise that could have been disturbed as the starter motor was replaced? The mechanic had trouble accessing it as its tucked high up behind the engine and was a struggle to get out apparently.

Does disconnecting the battery reset something? Some ECUs need to re learn the driving style before they apply a proper fuelling curve? I haven't driven it enough since the repair, to know if the display mpg is a true reflection of actual mpg - the gauge doesn't seem to be zooming down?

Any thoughts appreciated.

Thanks,

[X5Sport]

If it’s anything like the E46 then the intake manifold and all associated wiring has to come off in order to get to the starter (it’s high up on the RHS of the engine viewed from the front.

Disconnecting the battery is the standard first check for many modern cars and should have no impact on fuelling etc. BMW often suggest disconnecting it for 30mins and it doesn’t ‘reset’ anything in terms of what you suggest. The trip computers will zero out though.

[Alan Gunn]

It's because the battery was disconnected it reset everything.
After some days it will get back to normal.
Miles to empty would look low as well but it will all level out in a few day's.

[Leslie]

Battery was disconnected as said now you have current mpg for short runs which is usually woeful!

[ACintertec]

Thanks for your replies - seems I did jump the gun a bit. Now I've been on a decent run or two, mpg is back where it should be. I was quite happy with around 28mpg on a long country lanes run, plenty of rain, up/down hills/fords and my wife n 2 kids in the car.

One issue I encountered, the windscreen mists up horribly if you use the demist button - less so if you just use the blower controls on max and set it to blow at the windscreen.

So, today de - poo'd the guttering below the windscreen, cleared off a decent amount of soil and moss under the wipers and down where the bonnet hinges come up from. I also lifted out the pollen filter (which was damp) and cleaned up around the seals and the drain hole. One of the 3 clamps that hold the filter lid down was not clamped down - maybe that's why the filter was wet and why the screen mists up? Filter is now on a radiator - awaiting refitting and replacement at a later date.

Overall, I'm pleasantly surprised at the condition of body/paintwork down in all those nooks n crannies and under the bonnet in general. No rust or oil to speak of - just rather mucky with surface dust etc. Also found a Shell Helix branded zipper bag with a full 1L bottle of said oil under the PS front seat - hopefully that means its been fed decent oil by its last owner. Engine air filter looks pretty new and the oil seems quite fresh from smelling/feeling it too.

Enough of my observations - thanks for stopping by anyhow

[X5Sport]

Glad it’s sorted. I expect a lot of us are going to fund moss etc growing where it shouldn’t and misted glass once we start using them again. My X6 has only done 160 miles since March! Been WFH most of the time since then, and if the virus doesn’t come under control I can see more local lockdowns being needed meaning even less use.

My insurers are now offering refunds for owners with low mileages this year. Nice of them. Not huge amounts of course ...