[raptor_f22]

Driving the 330D, recently fitted brand new tyres which I know cause a drop in fuel economy but noticing quite a dramatic change (relative to my car which has been quite predictable) . Just wondered if there were any common causes I should look out for?

Typical drive - 26 miles down the motorway to work. Giving 41mpg used to give 47/48

Around town used to give 40ish now down to 36

Thought it might be the thermostat but not displaying failure symptoms. Could it just be down to the new tyres and drop in temperature outside?

[stevesingo]

Check the running temp on the OBC hidden menu.

Also, the composition of diesel changes for the winter to prevent waxing. This leads to lower mpg also.

[Digitalize]

Colder air is denser, so cars become a bit more powerful/thirsty in the winter, probably not a noticeable change though. It would have to be sub zero for it to really effect the engine in a meaningful way.

[Rustymage]

Handbrake dragging, brakes dragging, something trapped underneath, carrying more weight in the car, square tyres, grippy tyres....

[raptor_f22]

Thanks all, car going to indy for front brakes soon so will get him to see if it's anything mechanical but sounds like it's normal for the weather change then

[Rustymage]

Originally Posted by raptor_f22

Thanks all, car going to indy for front brakes soon so will get him to see if it's anything mechanical but sounds like it's normal for the weather change then

It could also be you're on choke for longer so using more fuel. Again, back to the weather.

[raptor_f22]

So a bit confused now - mpg seems to have plummeted even more

New pads and discs on the front - N/S/F is a bit "sticky" but not dragging, other than that I had a full vehicle inspection done and it's perfectly fine. However, mpg seems to be plummeting again

Indy said to keep an eye on the engine temp so managed to find the hidden menu today. Granted it's not a long drive but after 12 miles or so of driving I saw it vary between 68 deg - 75 deg max.

Is this normal or a sign my stat has died?

[E60525d]

You should easily get normal operating temperature in 12 miles. Sounds like you definitely need new thermostats.

I did mine last week and got 90 degrees in around 5 miles.

[Sensible_]

Originally Posted by raptor_f22

So a bit confused now - mpg seems to have plummeted even more

New pads and discs on the front - N/S/F is a bit "sticky" but not dragging, other than that I had a full vehicle inspection done and it's perfectly fine. However, mpg seems to be plummeting again

Indy said to keep an eye on the engine temp so managed to find the hidden menu today. Granted it's not a long drive but after 12 miles or so of driving I saw it vary between 68 deg - 75 deg max.

Is this normal or a sign my stat has died?

With temps that low your main thermostat has had it.

Basically the DDE control unit will send in more fuel to compensate for the low running temps. No wonder you are seeing reduced fuel economy. It's also likely to be restricting your DPF.

I'd get it sorted asap to avoid problems.

[raptor_f22]

Just drove to Gatwick and back - 90 miles in total. At 80mph the highest temp readout was 91 but average seemed to be in the 70s and around town in the 60s. Mpg claimed to be 39ish but the fuel needle had moved a lot more than normal considering it was a full tank to start with

What does it cost to replace the stat usually?

[Sensible_]

Hmm, if it's getting to 90+ that's good.

Although what was your driving like? When you are cruising temps should be high 80s+.

If you noticed the temp shoot up for a limited period of time then that could have been when performing DPF regen.

Re thermostats depends massively on what year/ engine you have...

If you have an M57 variant then you could have up to 3 thermostats:

Main, egr, auto box (if auto)

[raptor_f22]

On cruise control it was generally high 70s or bang on 80. I got it to 90 by flooring it for a while but I noticed that going up a hill at 80 the temp dropped to 68 which is thought was odd... But I dunno

It's the m57n2 and yeah it's an auto

[raptor_f22]

Been quoted 260 to replace both main stats

[Calluhan]

Originally Posted by raptor_f22

Been quoted 260 to replace both main stats

Ouch! Did mine myself with genuine BMW stats from Cotswold BMW for £86.

At the very least do the egr stat yourself it literally takes 10 minutes and a screwdriver!

[Deadlock]

Originally Posted by Sensible_

With temps that low your main thermostat has had it.

Basically the DDE control unit will send in more fuel to compensate for the low running temps. No wonder you are seeing reduced fuel economy. It's also likely to be restricting your DPF.

I'd get it sorted asap to avoid problems.

I think mine is gone too so going to put that video to good use!!


However, Its strange as I am still getting 47mpg (indicated) on a long drive to leeds on Tuesday and a 45.7 mpg driving down to Essex yesterday. Leeds too half a tank to do 360ish miles - so dont know.

My temps were around the 75 to 80 mark however!

[raptor_f22]

Originally Posted by Deadlock

I think mine is gone too so going to put that video to good use!!


However, Its strange as I am still getting 47mpg (indicated) on a long drive to leeds on Tuesday and a 45.7 mpg driving down to Essex yesterday. Leeds too half a tank to do 360ish miles - so dont know.

My temps were around the 75 to 80 mark however!

I think you're having a similar issue to me - one of the stats must be sticking, so at high speed when you're giving it some it works momentarily and the temp goes up (also because of the inc in ambient temp and convection from soak time). Today I was gunning it down the motorway and mpg went from 33 to 39 as the temperature went up.

As soon as I got off the motorway, the temp dropped and the mpg fell off a cliff again.

Got the car booked in for the 15th but hoping I can get it in before then, too much fuel being wasted every day

[Deadlock]

Originally Posted by raptor_f22

I think you're having a similar issue to me - one of the stats must be sticking, so at high speed when you're giving it some it works momentarily and the temp goes up (also because of the inc in ambient temp and convection from soak time). Today I was gunning it down the motorway and mpg went from 33 to 39 as the temperature went up.

As soon as I got off the motorway, the temp dropped and the mpg fell off a cliff again.

Got the car booked in for the 15th but hoping I can get it in before then, too much fuel being wasted every day

yep think so... very confusing mileage ok / mpg ok but what is not is the temps! they are not right. just comtemplating if I should do the egr first myself and see how that goes or just go for it and do both the main and egr at my indi