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Brucester
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PostWed Apr 22, 2020 1:48 pm 
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I came across online comments to YouTube video's on folks getting higher mpg while using the FWD mode. "5 mpg gains?"

I wonder if this works on newer models and if anyone has tried this and got better mpg? Any problems?

There was a mention of the manual not recommending this....
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Backpacker Joe
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PostThu Apr 23, 2020 3:51 am 
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That doesnt seem to make any sense to me. You cant possibly expect higher MPG's when you chose to add more stress to the drive train.  That engine stress will naturally lower MPG.

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"If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide."

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Gregory
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PostThu Apr 23, 2020 8:10 am 
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Do not do this to a car you value. The fwd is for testing diagnosing only. it takes the rear wheels out of the equation but how it does this will fail over time. I do not want to get into a lengthy explanation as it is all line for you to research your self but it will shorten the life of the transmission and they are not cheap. This practice is done by the Subaru hacks that are driving junkyard specials last I knew. Usually, because they have blown the rear clutch packs and the car binds making it difficult to drive on the street. The rear wheels only engage when there is a disparity in wheel speed from front to rear anyways so I do not believe the number and if you ever drive one with the fwd fuse in it slips all over the road when it rains. Probably why they get better mileage is you have to drive really light on the throttle. hope this helps.
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Backpacker Joe
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PostFri Apr 24, 2020 5:42 am 
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Are you talking about Front wheel drive mode instead of ALL wheel drive mode?  If thats the case then yes I can see an MPG improvement.  Then again, those cars arent bought for their MPG, they are bought for their capabilities.  Usually.

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"If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time or die by suicide."

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Opus
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PostFri Apr 24, 2020 6:55 am 
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I thought this was for use with the spare tire, at least in the older Subarus. The donut-spare is a different diameter so I was told to always install this on the front in my 2006 Outback. If the flat is on a rear tire, swap a good front tire out and put the spare up front. Then use this fuse to disable AWD to prevent drivetrain damage. I think newer cars with stability control can compensate for this on their own.
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Matt
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PostSat Apr 25, 2020 9:49 am 
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My 2018 Forester has the opposite instructions for the donut spare, strictly advising that it should only be used on the rear wheel.  That also seems more intuitively sensible, since the front wheel is handling steering and a greater share of the drive load during highway driving.

The cars quickly detected that one of the tires didn't match, and lit up my dashboard like a Christmas tree with warnings that it had shut down many of the automated systems, but drove fine otherwise.

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Cyclopath
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PostSat Apr 25, 2020 10:31 am 
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I'd think you would want the good tires up front for braking.
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Gregory
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PostSat Apr 25, 2020 12:51 pm 
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Putting a fuse into the fwd activator supplies full voltage to a duty selenoid which regulates line pressure to either the clutches or the viscous coupler engaging the rear-drive. The problem lies in that the solenoid is not designed to be run at full voltage all the time and they fry.  Some last longer than others.When the selenoid fries you are stuck in what is essentially 4wd. Huge drivability issues in the form of torque bind just like putting a 4wd truck into 4wd on pavement and trying to do tight turn. This torque bind creates a lot of heat which is the enemy of the automatic transmision. This leaves you paying a transmission shop at the worst or doing the research to replace the solenoid and maybe the clutches or coupler yourself. The selenoid is not that big a deal but the clutches and baskets etc... a little more complicated. This is how I remember it anyways its been a few years since I have had my head into this but I do have a dead suby from doing exactly this. lol

None of my owner's manuals mention anything about accessing the fwd system for spare tire usage just do not exceed fifty and get it fixed as soon as possible. It does wear on the clutches.

You can use it for towing but not to exceed 20mph and a distance of thirty miles. key on accesory and transmision in neutral. Prefered is a flat bed for sure.

This is why I loved the old 4wd subies. Front wheel drive a and great gas mileage running around town and 4wd when I need it in the woods. I actually have a first gen legacy awd I am converting to the old 4wd five speed manual.
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Opus
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PostSat Apr 25, 2020 6:42 pm 
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Matt wrote:
My 2018 Forester has the opposite instructions for the donut spare, strictly advising that it should only be used on the rear wheel.  That also seems more intuitively sensible, since the front wheel is handling steering and a greater share of the drive load during highway driving.

You're right. I was told this when I bought the car 13 years ago and forgot the details since I've never had to do this thankfully. Helpful thread on SubaruOutback.org here:
https://www.subaruoutback.org/threads/using-spare-tire.17680/

Quote:
"This is why the donut spare is installed on the back axle, and AWD fuse has to be installed. In the 2005+ models, the fuse disables the clutch control signal which in turn disengages the clutch. Now, even though the front and rear drive shafts are turning at different speeds, it is of no consequence because the rear drive shaft is disconnected from the drive system. Only the front drive shaft and front wheels remain connected to the transmission output -- the car is in FWD mode."
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