MPG Drop after full service

benv6 · Post by **benv6** » Mon Oct 17, 2016 1:50 pm

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 · Post by **Smartbear** » Mon Oct 17, 2016 3:45 pm

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 · Post by **mr wilks** » Mon Oct 17, 2016 3:47 pm

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

benv6 · Post by **benv6** » Mon Oct 17, 2016 4:28 pm

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 · Post by **mr wilks** » Mon Oct 17, 2016 4:41 pm

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 · Post by **Chris_D** » Mon Oct 17, 2016 4:42 pm

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 · Post by **benv6** » Mon Oct 17, 2016 5:05 pm

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 · Post by **mr wilks** » Mon Oct 17, 2016 5:11 pm

Chris_D wrote: 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 · Post by **goldbcfc** » Mon Oct 17, 2016 5:19 pm

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 · Post by **raymond.harper** » Mon Oct 17, 2016 5:56 pm

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

Chris_D · Post by **Chris_D** » Mon Oct 17, 2016 7:48 pm

mr wilks wrote:
Chris_D wrote: 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

buzyg · Post by **buzyg** » Mon Oct 17, 2016 8:29 pm

Smartbear wrote: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 · Post by **Doddsy** » Mon Oct 17, 2016 8:31 pm

mr wilks wrote:
Chris_D wrote: 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 · Post by **mr wilks** » Mon Oct 17, 2016 8:39 pm

Doddsy wrote:
mr wilks wrote:
Chris_D wrote: 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-LO ... SwwpdW227w

Chris_D · Post by **Chris_D** » Mon Oct 17, 2016 8:43 pm

mr wilks wrote:
Doddsy wrote:
mr wilks wrote: 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-LO ... SwwpdW227w

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.

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