MPG Drop after full service

[benv6]

Had my 35i for 3 months now. It had a full service 2 weeks ago , I used to average 28/29 MPG mixed driving.

After the service the MPG dropped to 22/24 MPG mainly smooth driving (2 tanks now)

I have done the brim thing and now I am getting about 250miles from (£54) instead of 300miles from £54 I used to have !!!

 

[Smartbear]

That's a huge drop, does it still run the same? I'd expect economy to dip as the temperature drops but not to that extent, are you doing shorter journeys in it? id go back to the garage & have a word.
Rob

 

[mr wilks]

Ask what oil grade & manufacturer was used , a thicker grade will have a negative effect on MPG from a thinner one

 

[benv6]

I have used Castrol Edge 0W-30 (Fully Synthetic with Titanium), new filters, new spark plugs.

When changed the oil the guy working on my car said that the oil was in a very "liquidy/watery form" and was very late for a change !! I use it mainly to commute so still the same use !!

 

[mr wilks]

Perhaps the mpg will rise slowly as the new oil thins although 0w 30 should already be giving max MPG ,
I do know whenever ive switched to Millers Eco or Nano the MPG generally rises but only marginally ( 1 - 2 mpg )
Has your garage got any ideas ?

 

[Chris_D]

Is the 'guy working on your car' an oild specialist?
I'd say that unless it looked like black treacle that most oils are watery, especially if up to temperature. And most oils will darken over time due to carbon accumulation and really can't tell what end of that scale you're at purely by looking or touching it.
0W-30 is no different to 5 or even 10W-30 when at operating temp. The lower viscosity just means it gets up to operating temp quicker if youre in a cold climate (?)
I would suggest an engine diagnostic/compression test/ dyno run to see if ur still on spec.
You could be running too rich, which would obviously use a little more fuel but over 2 tanks I'm not sure the drop would be that extreme.
As k what they did for the service including everything as a normal oil service shouldnt really have a detrimental effect on fuel economy.

 

[benv6]

The garage said the same thing as Mr Wilks, asked to give it some time.

And as Chris said, the oil was very hot when changed so it makes sense that it was very fluid.

I think I will give it a bit more time and see.

 

[mr wilks]

0W-30 is no different to 5 or even 10W-30 when at operating temp. The lower viscosity just means it gets up to operating temp quicker if youre in a cold climate (?)

I was meaning to ask in case the garage had used a 5w or 10w 40 (or semi synth) which could worsen MPG until the car was fully up to temp
Personally I wouldn't run any car i had on 0w 30 ok for hitting the best MPG but not best for protection of the vital parts as miles increase

 

[goldbcfc]

Did they change the air filter?. They probably aint reconected the air box properly or knocked a connection on air intake hose you may have slight maf / air miscalculation going on by the ecu to cause less mpg like that. No way would oil change the mpg like that only fuel and air

 

[raymond.harper]

Brakes binding ? Tyres pressures wrong ? Air con on all the time by mistake ? Wrong spark plugs used ?

 

[Chris_D]

0W-30 is no different to 5 or even 10W-30 when at operating temp. The lower viscosity just means it gets up to operating temp quicker if youre in a cold climate (?)

I was meaning to ask in case the garage had used a 5w or 10w 40 (or semi synth) which could worsen MPG until the car was fully up to temp
Personally I wouldn't run any car i had on 0w 30 ok for hitting the best MPG but not best for protection of the vital parts as miles increase

Agreed. I've always run 5W30 full synth on all my 6 pots.
Gonna try some of that Millers stuff next I think. Heard good reports round these parts :wink:

 

[buzyg]

That's a huge drop, does it still run the same? I'd expect economy to dip as the temperature drops but not to that extent, are you doing shorter journeys in it? id go back to the garage & have a word.
Rob

. I would expect it to improve with cooler temps. more dense fuel more dense air surely = more mpg. Not that I have ever measured it. Just boring physics. :? No doubt there is far more to it than just temp.

 

[Doddsy]

0W-30 is no different to 5 or even 10W-30 when at operating temp. The lower viscosity just means it gets up to operating temp quicker if youre in a cold climate (?)

Personally I wouldn't run any car i had on 0w 30 ok for hitting the best MPG but not best for protection of the vital parts as miles increase

Hi Mr Wilks, I put Castrol edge FST long life 04 titanium 0W-30 in my 2.5si at 55k. Now at 60k what would you use? 5W-30?
Cheers

 

[mr wilks]

0W-30 is no different to 5 or even 10W-30 when at operating temp. The lower viscosity just means it gets up to operating temp quicker if youre in a cold climate (?)

Personally I wouldn't run any car i had on 0w 30 ok for hitting the best MPG but not best for protection of the vital parts as miles increase

Hi Mr Wilks, I put Castrol edge FST long life 04 titanium 0W-30 in my 2.5si at 55k. Now at 60k what would you use? 5W-30?
Cheers

I would definitely be on to 5w 30 grade & my own preference is Millers so any of their fully synth range is top quality .
I would still change every 12 months or 7k though

http://www.ebay.co.uk/itm/MILLERS-EE-LONGLIFE-ECO-5W30-NANODRIVE-ENGINE-OIL-FULL-SYNTHETIC-5-LITRE-7706GG-/261534610299?hash=item3ce4ad737b:g:4GgAAOSwwpdW227w

 

[Chris_D]

Personally I wouldn't run any car i had on 0w 30 ok for hitting the best MPG but not best for protection of the vital parts as miles increase

Hi Mr Wilks, I put Castrol edge FST long life 04 titanium 0W-30 in my 2.5si at 55k. Now at 60k what would you use? 5W-30?
Cheers

I would definitely be on to 5w 30 grade & my own preference is Millers so any of their fully synth range is top quality .
I would still change every 12 months or 7k though

http://www.ebay.co.uk/itm/MILLERS-EE-LONGLIFE-ECO-5W30-NANODRIVE-ENGINE-OIL-FULL-SYNTHETIC-5-LITRE-7706GG-/261534610299?hash=item3ce4ad737b:g:4GgAAOSwwpdW227w

Dont know if it's verifiable but i used to do an oil change every 5000miles on a car that lasted me 270k miles and was still going strong until it was smashed into.
I reckon it could have easily done another 100k miles and a bmw tech told me it was prob due to my regular short-interval oil changes.
Jus sayin.

 

[mr wilks]

More the better Chris , i never go over 12 months or 7k so whichever comes around first , doubt i would ever do 7k in a year with one car though

 

[RickRob]

Are you sure that it's not that your £54 is just buying you less petrol following recent price hikes due to the exchange rate?

 

[Chris_D]

More the better Chris , i never go over 12 months or 7k so whichever comes around first , doubt i would ever do 7k in a year with one car though

I only decided to do it so regularly as the car was my workhorse for getting me around Europe visiting clients in Poland, Germany and Switzerland. I used to take advantage of the derestricted sections of Autobahn in Germany especially and cruised effortlessly at 130-140mph back home to Holland. Hence, the thinking was longevity of the engine and regular oil changes as preventive maintenance.
The last compression check revealed a within-spec reading of factory-fresh on 5 of the 6 cylinders and the 6th not far behind. I might add that it was never revved hard and never saw the redline or limiter.
So I would certainly recommend regular oil changes to anyone even though not ultimately verifiable. Obviously motorway miles at high compression rates can only help but other dynamics will have an influence on how long any given engine will last.

 

[flybobbie]

My mpg on the 23i has gone down a few miles.
Cooler air means more fuel being pumped in, more power, less mpg.
You don't get howt for nowt.
What we call density altitude in aviation.

 

[goldbcfc]

since when did an oil change cause bad mpg....lol

it most likely the fuel and air mixture if you have turbos then it more noticable