Poor MPG

[Wildfire]

When the UK switched to e10 I noticed a drop in mpg for all the cars. The Z4C would get 39-42mp on a nice steady run, now now way. 36-38 maximum with really careful driving.

I think in the US you have lower octane fuel than the UK generally?

[Jacobkayne]

Check for a vacuum leak. When I fixed my oil cooler gaskets mpg went up so much it, I couldn’t believe it. Check oil cooler / oil filter housing gaskets, as well as valve cover gasket. Leaking air into the system will use more fuel and run less mpg

[colb]

Take a look at the fuel trims using a decent scan tool, high trims c an be as a result of air leaks that the exhaust sensor is picking up as unmetered air that has not been measured by the Maf sensor. Air leaks in the engines vacuum system after the Maf will cause the computer to see this as a lean mixture and try and compensate by adding fuel at the injectors to richen it up. It will continue to add fuel until its introducing 20% more fuel before it realises something is wrong and it will eventually light the EML to draw attention to the fault and set codes in relation to the fuel trims being high. MPG will be affected and you will be visiting the fuel station frequently.
Air leaks can usually be pinpointed by doing a smoke test, some can be hidden and easily missed doing a visual check. Splits or holes in the intake rubber bellows are the most common but also check the rear underside of the intake manifold where there are rubber blanking caps that perish and fall off allowing air leaks. If you have a dipstick also check the O ring in the dipstick tube for any leaks. Smoke is the best way to find small leaks. Have seen plastic cam covers develop cracks and allow air in as well as oil out, smoke found the leak in one I worked on.