[Chrism21]

I just got my new to me e90 back from the detail shop and noticed a considerable mpg drop. When I first picked it up 2 weeks ago I couldn't get the computer to move from 26.7 mpg (even in the city) and now after picking it up it dropped to 21.9 I read that at 100k you're supposed to change things such as spark plugs but what else am I suppose to change? Judging by the way the previous owner left her I can assume she didn't touch anything under the hood. I have never done a DIY but always willing to learn. Thanks.

[Two Snails]

Spark plugs, transmission fluid, and a walnut blast.

That should completely wake up your E90

[dbond]

that 26.7 mpg is probably averaged over of thousands of miles. It was reset in the shop and showing your driving style numbers now.

btw, no walnut blast for N52K engine

[Chrism21]

Originally Posted by dbond

that 26.7 mpg is probably averaged over over of thousands of miles. It was reset in the shop and showing your driving style numbers.

btw, no walnut blast for N52K engine

Forgive the ignorant question I'm
About to ask but the N52 is the 328i engine?

[shuaige]

Originally Posted by Chrism21

Forgive the ignorant question I'm
About to ask but the N52 is the 328i engine?

Yes.

I doubt you have the SULEV N51, which doesn't need the intake valve blasting either.

[Chrism21]

Originally Posted by shuaige

Yes.

I doubt you have the SULEV N51, which doesn't need the intake valve blasting either.

How can you tell the difference between the N51 and N52?

[shuaige]

Originally Posted by Chrism21

How can you tell the difference between the N51 and N52?

There's a sticker with emissions information under the hood. Or just enter your VIN on bmwvin.com or a similar site.

[Antetokounmpo]

Originally Posted by Two Snails

Spark plugs, transmission fluid, and a walnut blast.

That should completely wake up your E90

You don't need to walnut blast a port injected engine.. the fuel cleans the valves for you..

[DJtoad]

Also, remember that mileage will go down a bit with Federally-mandated winter-blend gasoline plus the engine will run richer until fully warmed up. That combination can affect your mileage by 10-20%.

[NiNeTyOne]

Air filter, cabin filter, plugs, transmission fluid, accessory belt & tensioner was what I did (and all the fluids including flushing the power steering). I'm about to also do all the wheel bearings and replace some bushings with PowerFlex bushings to tighten up the front end a bit as it seems to be a bit soft at speed.

I switched to Brisk racing plugs as I had them in my tuned/built bi-turbo Audi S and I love them. They last a LOT longer and I am sure the car is smoother.

I also tested the coils and they were all fine.

I have been pouring 300ml of LiquiMoly Ceratec into the crank case every 20k now (every fourth change) as well and changing oil every 5000mi with Liqui-Moly 5/30 and my valve train sounds like a new car.

I also pour a can of Seafoam into the tank with every 4th tank to keep things nice and clean.

[JustDriveIt]

Originally Posted by DJtoad

Also, remember that mileage will go down a bit with Federally-mandated winter-blend gasoline plus the engine will run richer until fully warmed up. That combination can affect your mileage by 10-20%.

Winter gasoline......what?

[Dozhdbog]

Originally Posted by JustDriveIt

Winter gasoline......what?

Ohhhh, young padawan.... you have much to learn.

:smh:

[JustDriveIt]

Originally Posted by Dozhdbog

Ohhhh, young padawan.... you have much to learn.

:smh:

Clearly, I think of myself to be fairly well educated and up to date and honestly had no idea about this.

[ctuna]

Google Mike Miller BMW
download the old school maintenance schedule
and read.
All fluids , All Filters and plugs would be good start.
Maybe the serpentine belt and tensioner.
And inspect for oil leaks.

[tlow98]

tire pressure is also a good place t look when first searching for mileage issues

[VTECaddict]

Stuff that is not tracked by the car's CBS (condition based service) system that you should probably take care of:
-Accessory belt/tensioner/idler pulley
-Transmission fluid
-Differential fluid
-Power steering fluid

Do you have any maintenance records at all? The following should have been done at regular mileage/time intervals but if you're not sure if they have been done or not then it might be a good idea to just do them anyway:
-Spark plugs
-Brake fluid flush
-Oil/filter change
-Microfilter
-Engine air filter
-Wouldn't hurt to run a bottle of Techron concentrate through as well (do this before an oil change)

Common failures to keep in mind if they haven't been taken care of already:
-Water pump/thermostat
-Oil filter housing gasket leakage
-Oil pan gasket leakage

[robthewrench]

Overtime the O2 sensors tend to lose their range and sensitivity. Replacing these on a 100K mile car can often get you back ~2-5% fuel economy.

[Two Snails]

Originally Posted by dbond

that 26.7 mpg is probably averaged over of thousands of miles. It was reset in the shop and showing your driving style numbers now.

btw, no walnut blast for N52K engine

Originally Posted by Heel Toe

You don't need to walnut blast a port injected engine.. the fuel cleans the valves for you..

I didn't know his was a 328, I assumed it was a 335

[NiNeTyOne]

Originally Posted by robthewrench

Overtime the O2 sensors tend to lose their range and sensitivity. Replacing these on a 100K mile car can often get you back ~2-5% fuel economy.

Especially for the primary O2's, I whole heartedly agree.

[Sara]

Buy new!

[Sidewinderpb]

Drive it into a lake. That's what in going to do.

[Antetokounmpo]

Originally Posted by Two Snails

I didn't know his was a 328, I assumed it was a 335

One does not simply get 27mpg in a 335. And look at his info next to his post..