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2007 Forester 2.5x
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Discussion Starter · #1 ·
Ok, so when you get a flat tire, you're supposed to put the car in FWD mode via a fuse. Wouldn't it make sense thagt switching out of AWD would result in higher MPG? I'm thinking that 80% or more of the time in my area there isn't any advantage to AWD for your average 9-5 commuter...

Has anyone tried this? Any negative consequences?
 

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2009 Outback XT-B 5MT
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No. All of the AWD components still spin, so there's no real advantage.

PLUS, the AWD fuse is a temporary fix ONLY. It is not to be used continuously.
 

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Ok, so when you get a flat tire, you're supposed to put the car in FWD mode via a fuse. Wouldn't it make sense thagt switching out of AWD would result in higher MPG? I'm thinking that 80% or more of the time in my area there isn't any advantage to AWD for your average 9-5 commuter...

Has anyone tried this? Any negative consequences?
Don't do it, it is not fun at all. The car hops around like crazy, it's really not designed for FWD. You could go out and try it for a few minutes, going around corners and accelerating= huge torque steer and spinning tires (especially if you have an XT)
 

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2004 Forester XT Premium 4EAT
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27,871 Posts
Also, the FWD solenoid is not designed for a 100% duty cycle....
 

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2009 Outback XT-B 5MT
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It's not just the FWD solenoid, it's the AWD solenoid being locked open. Continiously running at 100% duty cycle will burn out that solenoid. I think the appropriate result of that is Torque Bind as Duty Solenoid C no longer responds and simply remains at 0% Duty Cycle, effectively locking the center "differential".

I don't know a ton about Automatics, so someone correct me if I'm wrong about that. But I do know it's not good to roll in FWD for too long.
 

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2009 Outback XT-B 5MT
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Get a flat on the front, swap a rear wheel to the front and put the spare on the rear. Then install the FWD fuse and drive to a tire shop.

That's the procedure for automatics, IIRC.
 

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2007 Forester 2.5x
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11 Posts
Discussion Starter · #11 ·
Maybe I'm missing something.

Maybe the AWD system doesn't like being in FWD mode for any length of time, but I've never heard of a solenoid burning from being enabled for any duration of time.. Kind of like your light switch wearing out because you leave the light on all the time.

I've read on other forums about people using FWD mode for various reasons (dyno/emissions testing, rear differential problems, drag racing, and of course flat tires). I'm guessing, based on current feedback, that nobody has actually tried this. I'm not, of course, saying that its a good idea.
 

· Super Moderator
2004 Forester XT Premium 4EAT
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Maybe the AWD system doesn't like being in FWD mode for any length of time, but I've never heard of a solenoid burning from being enabled for any duration of time.. Kind of like your light switch wearing out because you leave the light on all the time.
That's not really an accurate comparison. Under normal circumstances the solenoid's highest duty cycle is around 90% from what I understand. So it continuously turns on and off many times a second with a certain amount of resting time in between. It is not outside the realm of possibility that running it at 100% duty cycle over a longer period of time could wear it out prematurely.
 

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2004 Forester XT
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301 Posts
That's not really an accurate comparison. Under normal circumstances the solenoid's highest duty cycle is around 90%. So it continuously turns on and off many times a second with a certain amount of resting time in between. It is not outside the realm of possibility that running it at 100% duty cycle over a longer period of time could wear it out prematurely.
From a mechanical stand point, I'd have to agree. Most mechanical devices (compressors, motors, etc.) have duty cycles for various reasons, but they all have the same goal.. to avoid premature failure of the part. Sometimes its a motor that gets hot, and needs time to cool down... sometimes it is a hydraulic piston that can warp or deform under constant stress...

I just don't like the idea of making anything do what it isn't designed to do, unless it is for a short duration.
 

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1998 Forester S
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340 Posts
Since this can only be done to the AT cars, would this be the reason I have a full sized spare? (I have a MT). And why wouldnt they just put a full sized spare in all the cars instead of having to do this fuse thing when encountered with a flat?

Just seems like common sense to me, thats all.
 

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2004 Forester XT
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301 Posts
Since this can only be done to the AT cars, would this be the reason I have a full sized spare? (I have a MT). And why wouldnt they just put a full sized spare in all the cars instead of having to do this fuse thing when encountered with a flat?

Just seems like common sense to me, thats all.
Another really GOOD point. I just assumed that all Foresters had full sized spares. If the 5EATs don't, then that could explain it... but as you said it just doesn't make sense.
 

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2004 Forester XT Premium 4EAT
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Since this can only be done to the AT cars, would this be the reason I have a full sized spare? (I have a MT). And why wouldnt they just put a full sized spare in all the cars instead of having to do this fuse thing when encountered with a flat?

Just seems like common sense to me, thats all.
The procedure with the fuse also applies to Subarus with a full-size spare (to compensate for differences in rolling circumference if your tires are worn significantly more than your spare). Take a look at your owners manual, it should be outlined in there. I know it is in mine.
 

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1998 Forester S
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340 Posts
ahh right because if they are more the 1/4 of an inch different it is bad. I forgot about that. Learn something every day I guess and will be good to know if I ever own a AT subby.
 

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2007 Sport XT
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1,128 Posts
Maybe the AWD system doesn't like being in FWD mode for any length of time, but I've never heard of a solenoid burning from being enabled for any duration of time.. Kind of like your light switch wearing out because you leave the light on all the time.
A solenoid isn't just a switch, which is a passive device and (assuming the switch contacts are in good condition) draws no power. A solenoid though is an electrically operated device, and that means it draws power to operate it. Drawing power means it will generate a certain amount of heat. If it isn't designed to be activated permanently, it may well overheat and burn out.

Having said that, surely Subaru must have designed it to operate for hundreds of miles in FWD mode. I've not seen any restriction on mileage while in FWD mode. (I'm not advocating leaving the car in FWD mode unnecessarily though.)

BTW, VDC equipped automatics don't have the FWD mode. It appears the VDC is supposed to take car of it itself, they do have an almost full-sized spare wheel which must help too.
 

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2005 Forester XT 4eat
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4,499 Posts
This is strange...

My owner's manual says nothing about putting a rear wheel on the front of the car in case of a flat tire, and doesn't mention putting in the FWD fuse either. I have a 2005 XT with an automatic with a full size spare. The manual says 2005 Forester Owner's manual on the side. On the back, it says "Issued April 2004" and "Printed in USA" under that. It also says "2005A"

Can someone else confirm this? I wonder why mine says nothing about this.:icon_confused:
 

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2004 XT AT
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1,105 Posts
@guroove Mine's the same (2004 XT auto, UK model). The FWD fuse is only mentioned with regard to being towed, not when talking about the spare tyre. Mine also has a full-sized spare by the way.

The manual also says nothing about the famous quarter inch tyre wear rule either - it just makes some general statements about trying to keep the tyre wear even, but all car manuals say that, even for 2wd cars. I'm sure if the quarter-inch thing was as critical as people say, it would be in big bold letters in the manual. I bet most owners don't even know about it and yet Subarus have a fantastic reputation for longevity and reliability.

-- Steve
 
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