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2010 Mercury Milan Hybrid - MPG going down

My Mercury Milan Hybrid is gradually getting poorer and poorer mileage. Over the years it has gone from 38-39 MPG down to 32-33. I have replaced the spark plugs and the air filter with no change in the MPG. Any idea why?

Are you using the same make and model tires? Is it seasonal? Are you checking the MPG at the pump or using the car’s digital display to tell you the MPG?

Does this dip in fuel economy seem to correlate to cold weather? If so, that’s expected.

How often do you check your tire pressure?

There was some talk about a built in 10 year timer on Ford hybrids that limits the electric operation of the powertrain after a ten year period. It doesn’t disabled the hybrid part of the powertrain, but after ten years the electric motor is used less, supposedly this was done to prolong the life of the high voltage components. It can be corrected by turning back the date on the hybrid system.

Here’s that discussion:

My '11 MKZ hybrid dropped a couple of mpgs when I switched tires.

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I did some googling, found this solution, which I have NOT tried, so no guarantees!

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I read about 2 pages of the comments on that Ford Fusion Forum

There was a guy with a 2010 Fusion Hybrid with 300K that performed the “reset” procedure, and he reported a dramatic increase in fuel economy.

I kind of wonder how long his battery will last, given that the control module(s) are now under the impression that the battery is essentially new, versus the old high mileage battery that it in fact is . . .

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As far as I know Toyota doesn’t resort to this, their batteries last fine. I’d rather get full benefits, then deal with the battery issue if it comes up.

For unexplained reduced mpg the first check is to make sure the gasoline engine is reaching normal operating temperature. Faulty coolant thermostats that cause the engine to run too cool is the most common cause for this problem. Is it still the original thermostat?

The change has taken place over 10 years and doesn’t seem to have anything to do with the tires

The tire pressure is checked every time I have the car serviced. The drop has occurred over 10 years time and is not temperature related. Plus, I live in the SF Bay area and we don’t have big temperature changes in the winter.

I don’t know if it has the original thermostat. I’ll check. Thank you.

So, apparently you noted significant reductions in your MPG during the warranty period.
What was the reaction from the dealership to your complaint?
If you elevated your complaint to the corporate level, what was the corporate response?

And, if you didn’t elevate your complaint to the corporate level 9 or 10 years ago, I have to wonder…

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Is the hybrid battery degrading? You may need to replace some of the cells in the hybrid battery. You need a qualified shop to test the battery.

Did you read the links I posted? Ford/Lincoln/Mercury hybrids have programmed their cars to have their battery power cut back starting in the 8th year or so. I just did the fix recommended in the link to my 2011 MKZ hybrid, and it restored both the mpgs and the power. It had dropped from 37 to 33, now it’s back to 37.


The dealer fix a few things. Replaced an oxygen sensor. There was no charge. These parts were still under warranty at least in California. The service rep said Ford is working on it and they will let us know when they get an answer from Ford. If I don’t get any help, how does one elevate the complaint to the corporate level?

I’m not as mechanically or technically inclined. I sent the information to the dealer to see if they would do it.

The battery seems to be fine. It is charged fully or almost fully most of the time. It seems that the car is only using the gas engine.

By simply opening one’s Owner’s Manual, and reading the details contained within that booklet. Therein, you would have found a toll-free phone number, as well as a mailing address to which you could have sent Certified Mail copies of your complaint(s) to Ford, at the corporate level. Sad to say, you are many years past being able to avail yourself of that type of assistance.

For future reference, with your future vehicles, all I can suggest is that you avail yourself of the possible remedies that are outlined in your Owner’s Manual.

Other Fusion/Zephyr/MKZ hybrid owners have had hit-or-miss luck with dealers. Many refuse to do it.