mileage dropped at 50,000 miles

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#1
My 2013 fusion hit 50,000 miles earlier this year; I had been getting 46.5 mpg consistently and after the 50,000 mile mark it's dropped to 41-43. Not related to winter vs summer tires or winter ethanol in the gas. My mechanic could not find anything wrong at the 50,000 mile service. Very disappointing. Any ideas?
 

Handy Andy

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#2
IT's a Hybrid - so was the battery(ies) looked after?

Usually the battery/hybrid system - begins to degrade after time - they can no longer hold as full or length of full charge rate after a period of time. Its' based upon technology from 2013 - till present - which is now the latter part of 2022.

Lithium or a hybrid of such, has only a limited lifespan of charge to discharge to recharge cycles, just like any ordinary lead plate (lead acid - NiCd NiMH inclusive) that uses an electrolyte as a catalyst or means to separate charge - have limited lifespans - no matter what.

So perhaps the degradation is due to the battery-performance sensing units - seeing that the batteries are needing more effort to keep topped off, the system has modified the hybrid profiles it uses for in obtaining good mileage versus use of charge to recharge cycles to your required performance needs (your driving may not have changed - the reserve capacity of the system though, has.) - those profiles have changed. The engine runs longer because the batteries don't deliver like they used so - so some work is needed to restore the OEM you once had, only now it will get expensive to replace the batteries and any other sub-systems needed to be maintained will also need servicing. Else the 41MPG - you'll have to rework your driving habits to restore that which is in decline - which only buys you some time and only defers that what you already know, will eventually have to be done to restore the performance it once had.

The mechanical systems may be fine, but the electrical systems side is what might be changing your mileage - forcing the engine to recharge the battery system more often and for longer periods of time.
 
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Thread Starter #3
Thanks for comments about the battery, which I'd been told would last until 125,000 miles but no one suggested its performance would wane in the meantime. I''ll look into this. I certainly wouldn't plan to replace the battery so if adjustments cannot be made, I guess I'm stuck with disappointing mileage....
 

Handy Andy

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#4
If you need to know where I'm getting information like this from, I did a simple search looking for Ford Hybrid Battery Warranty - which is typical 8 years.

I'd recommend you start here...
https://myvehicletalk.com/ford-fusi...00,000 miles covered, whichever happens first.

Now as far as Mileage, the battery is not seen as "miles" travelled, more like duration of its life-cycle - which is more along the lines of time. You can travel a lot more miles in 8 years and the battery would work fine during that time, but after a length of time, the battery - due to those cycles of use for all those miles - will exhibit degradation of its ability to charge, hold a charge and rate of discharge - as it will be a much steeper downward slope curve - versus a gently used battery of similar design but less used (or miles driven) by it.

To help get this into perspective - the Lead Acid battery found in most of today's cars is a simple two dissimilar metal plates suspended in an electrolyte and a spacer. Lithium-Ion types are similar in design except they use Lithium in an electrolyte solution for form ions when it is fully charged - these Ions recombine and in doing so, release power in the process.

Lead Acid batteries have only so much length of service life and shelf life, for the maximum life span is its ability to withstand the Sulfuric acid in the solution in the container, the housing, the metal the plates are and the dielectric - or spacer to keep the plates from touching and shorting out the cell. This life span is reduced if the battery sits filled with the solution it will have to work and use in its life - when empty and sealed from oxygen - the battery is not charged, only ready to be placed into service, then ready when filled. When they put a battery into use, it is filled with this sulfuric acid and is considered fully charged.

Lithium-ion designs are more durable in extreme environments - while the solution of Sulfuric acid used in the lead - acid battery type - has a specific gravity and also is much more environment temperature sensitive.

Not to get too technical...
But your Dad, may have used this device
A Hygrometer, in some form to check his car battery.
1672004305014.png
  • As a sidebar:
    • These testers were (in some cases still are) popular in both battery and in Antifreeze testers.
    • Sulfuric Acid was one of the mediums Fahrenheit used to show temperature as a freezing point of a fluid into a solid - typical Battery Acid (straight form not modified) freezes at 0F - not 32F like water does - at sea - level atmospheric pressure.
    • SO2 (Sulfuric) Acid will also boil at a lower temperature than that of water 212F versus ~185F.
    • And is more sensitive to these triple points at lower atmospheric pressures (mountains and elevations) above Sea level.
So, to make a long story short, you'll need to monitor the batteries in that car - for they are approaching the maximum useable life span, in time, and can expire - unexpectedly, due to their failure.

You can't use a Hygrometer in the Lithium Ion designs, only by their ability to hold charge and not drain due to their internal resistance generated by suspension of electrolyte and dielectrical isolation of their separation of charge in the plates - so that uses a circuit like a battery monitor in a smoke alarm, to determine the batteries Go or No-Go condition.

Your decreased MPG due to increased use of the engine- is one of these tell-tale signs.
 
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Thread Starter #5
IT's a Hybrid - so was the battery(ies) looked after?

Usually the battery/hybrid system - begins to degrade after time - they can no longer hold as full or length of full charge rate after a period of time. Its' based upon technology from 2013 - till present - which is now the latter part of 2022.

Lithium or a hybrid of such, has only a limited lifespan of charge to discharge to recharge cycles, just like any ordinary lead plate (lead acid - NiCd NiMH inclusive) that uses an electrolyte as a catalyst or means to separate charge - have limited lifespans - no matter what.

So perhaps the degradation is due to the battery-performance sensing units - seeing that the batteries are needing more effort to keep topped off, the system has modified the hybrid profiles it uses for in obtaining good mileage versus use of charge to recharge cycles to your required performance needs (your driving may not have changed - the reserve capacity of the system though, has.) - those profiles have changed. The engine runs longer because the batteries don't deliver like they used so - so some work is needed to restore the OEM you once had, only now it will get expensive to replace the batteries and any other sub-systems needed to be maintained will also need servicing. Else the 41MPG - you'll have to rework your driving habits to restore that which is in decline - which only buys you some time and only defers that what you already know, will eventually have to be done to restore the performance it once had.

The mechanical systems may be fine, but the electrical systems side is what might be changing your mileage - forcing the engine to recharge the battery system more often and for longer periods of time.
Hi, Andy: thanks again for this very helpful information and the link. I mistakenly believed what the salesman told me - that the HV battery would last 125,000 miles, but I now see that the warranty is for only 8 years. So I need to consider repair or replacement, even though I don't expect to keep the car more than another few years. That sounds expensive but would help resale value. (I don't know anyone with a Fusion hybrid but know lots of people with Priuses (many much older) but none of them has mentioned a deteriorating HV battery.)
 

Handy Andy

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#6
(I don't know anyone with a Fusion hybrid but know lots of people with Priuses (many much older) but none of them has mentioned a deteriorating HV battery.)
Quite possibly due to the fact that Hybrid vehicles - many older ones have a backup (loose term - but Automotive) standard battery for the engine - but the specialized HV battery and its output - needs to be kept from the ignition system - so the combustion-engine side has its own 12V system battery.

The HV side is a 200V system - so you've been warned - and it's NiMH type.

They too, are not immune to the loss of EPA-MPG - so the batteries in those vehicles have to be and often do, get replaced.

You do sometime see a Prius of an older year that has the HV specialized battery replaced - and as long as it's "caught" within a reasonable amount of time before degradation got too extreme - their resale value is / has gone up due to initial up front cost of the new battery dropped in - took much of the loss incurred into a workable resale value for the vehicle.

But to start the engine - it still uses a typical 12V auto battery.
 
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Thread Starter #7
thanks so much for all this information about batteries - I've learned a lot!
 

Handy Andy

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#8
I wish you the best in whatever choice or course you choose - it's expensive to fix in the short-term, but if you like the car - keep it and just reinvest into it - else getting a new one limits your choices even more.
 


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