Forester in FWD Mode - bad idea or save $$

[friendly_jacek]

That makes no sense. First of all, having the fuse in puts the solenoid in 100% duty and 100% of the power is transfered to the front wheels. Secondly by your logic, a 5mt would get 40% worse gas mileage than a 4eat. but we all know that 5mt's get better mileage. Also by your logic, if one was to disconnect the soleniod all together you'd be getting 100% power to the rear wheels and as such would be getting 100% worse gas mileage, and that's just redicilously silly.

Well, I am no expert. I just felt like speculating.

Nevertheless, I am not going to argue with your posts because:

 

A. I probably did not understand them correctly, or:

B. If I understood them correctly, your insight into AWD is limited.

[Danbob99]

i've got a fwd switch i rigged up on my car, seems to work just fine, i figure as long as i only leave it in fwd for short periods of time i'm not going to to drain the atf out of the clutches that put it into awd, think thats what mike was telling me could happen...

but yea, it works just fine for me...i don't see a problem running it for short periods of time, i don't know about running it for months at a time like that though.

[JOEK39]

why does it get better mpg? You are still turning all that drivetrain via the rear wheels.

The drivetrain is turning, so there is a slight hp (mpg) loss due to that, but since you are not DRIVING the rear drivetrain, there is a HP and milkeage savings.

[friendly_jacek]

With gas getting expensive, i decided to experiment and put the tranny into FWD mode (fuse insertion). No detectable change in driving, but I have averaged 28 mpg over 2 tanks of gas - thats a 27% improvement!

I know it was a long discussion and covered everything, but is the MPG improvement sustained?

Did you change anything alse, like resetting ECU at the same time?

Toying with this experiment in mine.

[JOEK39]

Filled tank on Saturday ($2.09/gal ) Last tank of gas averaged just under 25 mpg. Had Alot OF RAIN last couple days and more predicted for the week, so I pulled the fuse on Saturday and back in AWD mode for awhile - safety first! and we'll see what kind of mileage I get.

 

Summary so far:

AWD mode 20-23 mpg

2WD mode 25-28 mpg

 

The experiment continues!! :cool:

[friendly_jacek]

Hi,

 

I hope everyone had a nice Holiday.

 

I had and put 1200+ miles on my 2000 legacy wagon AT in the process. I tested the FWD thing, alternating tankfulls between FWD and AWD (you can take this as "randomization"). The results: AWD 23.3-25.1, FWD 23.6-24.7 MPG. Did not do statistical analysis, no need, the numbers look very similar and averages are almost identical.

The conditions were: Hwy, cruise control, 80 mph, AC, moderately heavy load, temp 80-90 F, essentially sea level. There were only occasional spots of congestion on hwy.

I also tried the study in the city driving only: AWD 16, FWD 15.3 MPG. However, this was limited by low number of miles (my wife does only short trips during weekdays).

 

It looks that FWD does not save gas for me. I am surprised that it works that well for JOEK. I see no possible explanation.

 

BTW, I have synthetic fluids in the engine and drivetrain and near max air pressure in the tires (~40 psi). No codes in the ECU ot TCU.

[JOEK39]

Back in AWD mode for the last 2 tankfuls of gas, averaged 23 mpg. For me, and this vehicle I'm getting a 2-3 mpg improvement in 2WD mode (25-26 mpg).

 

For me, that equates to a savings of about $100 per year. I'm not sure if thats worth it from a safety and handling standpoint, and there's still no clear concensus on whether I'm doing any damage to the tranny.

 

So unless gas goes to $5 a gallon, I think I'll stick with AWD.

 

Thanks for EVERYONES informed opinions - this was an interesting discussion.

[Brambler]

I have a '99 Impreza Outback, and the guy I got it from said the u joints and the tranny needed replaced.

I asked if it would be possible to take out the driveshaft and pop the fuse for fwd, and was cautioned not to do that.

So, how much work is this gonna be?

[golucky66]

If it was just the u joint, sure thatd be fine.

But if there's an issue with the tranny. Putting in the FWD fuse isn't going to change a tranny issue. (unless its related to the tail of the tranny)

[Brambler]

Clutch needed replaced, not tranny, sorry. I'm half dead from a solid 16 in the snow and rain.

[golucky66]

So the FWD fuse won't really... Help with the clutch issue.

U-joints for sure.

But if it needs a clutch, it needs a clutch.

[Brambler]

Ok, I figured it wouldn't help the clutch at all, but I have a couple of questions:

1)Will driving it while in fwd damage and of the running gear? Should I remove the rear drive line, if I do?

2)How much work will changing the clutch and/or drive line be?

[golucky66]

Wait a second...

 

If your car has a clutch, It's therefore a manual. And manuals don't have a fwd fuse because the front to rear power shift is done with a viscous cuffler not a clutch pack like on the autos.

 

So if it DOES have a fwd fuse and it is a manual. It ain't going to do anything.

[Brambler]

Ugh I'm so confused lol

So the fuse that has fwd written on it doesn't affect that at all?

And, sorry, yes it is a manual transmission.

 

So...that leaves me with fixing it, yes?

So how much work will clutch and u joints be?

[idosubaru]

Only autos have fwd capability.

 

Manual transmissions don't have a fwd fuse. The 4WD is strictly mechanical and varies via a self contained VLSD which is impossible to control electronically.

 

A failed VLSD transmission could be run in 2wd though. Pull driveshaft and drive it. But that only works if it's failed completely.

[golucky66]

That's really weird that it has that. Unless that manual transmission has been swapped in.

 

But realistically it shouldn't do anything because the front to back power it co trolled by a fluid that just get hot or cold...

 

You should have both jobs done together because the driveshaft has to be pulled in order to replace the clutch. So you'd save on labor a little.

 

In my area (fairly expensive area) It's probably 700-800$ to do the clutch. And probably only 50$ more to do the u joint.

 

Why does it need a clutch anyways? Does it not fully engage/disengage? Is it slipping?

 

But. If it does actually need a clutch I would strongly suggest fixing it. Unless you plan to get rid of the car soon.

Edited December 1, 2016 by golucky66

[calinaki]

Hi,

couple thoughts...   The fuse has been added so if you ever have to drive on a donut spare tire, you can switch to FWD and not worry about putting wear on your AWD system due to uneven tire diameters and grip.  My guess is Subaru did not put a switch on the dash because if you drove your car for 6 months in FWD and 6 months in AWD, you wouldn't wear your tires evenly, and you risk excessive wear on the AWD system over time.  Same philosophy behind always gettng a full new set of tires (not mixing and matching unevenly worn tires) on a Subaru AWD system.

Thanks.  

[idosubaru]

2 hours ago, calinaki said:

Hi,

couple thoughts...   The fuse has been added so if you ever have to drive on a donut spare tire, you can switch to FWD and not worry about putting wear on your AWD system due to uneven tire diameters and grip.  My guess is Subaru did not put a switch on the dash because if you drove your car for 6 months in FWD and 6 months in AWD, you wouldn't wear your tires evenly, and you risk excessive wear on the AWD system over time.  Same philosophy behind always gettng a full new set of tires (not mixing and matching unevenly worn tires) on a Subaru AWD system.

Thanks.  

First post digs up an 18 year old thread, were you looking for something?!

You're right to discourage using the FWD fuse beyond anything except the intended use or by those very familiar with Subaru's initiating repair options. There's no reason to and it won't offer any gains, mpg or otherwise. 

Subaru didn't design this system for long term use - that doesn't mean it can't do it. 

Subaru's more pressing reasons would be money.  No reputable business wants a feature like that easily accessible by occupants of the vehicle. They would be too easily confused about when/why it should be used. And it would be perceived as dangerous in the event of a wreck/lawsuit.  No way in a billion years Subaru would put that functionality at the whims of whatever person or pet is in the cabin, particularly given the general consumer focus of Subaru's offerings.  This lesson Subaru was *reminded* of when they got sued for Subaru brat rear seat injuries in the 1980's. 

Subaru also didn't design this system to be used *at all* while driving. So the location of the fuse is indifferent from a design perspective. It just needs to be found by anyone with minor mechanical reasoning or willing to read the owners manual in the event of a tire blown or accident on the side of the road. 

Many people have driven in FWD for long periods of time with no issues. It's silly to do it for "gas savings" reasons though. I have done it for repair reasons, both short term and life of vehicle (far more than 6 months), but definitely not for performance or gas mileage. 

If you take these transmissions apart there's nothing noteworthy that running in FWD will do.  As a matter of fact there's almost no difference between the 4WD and FWD automatics. You can take one out and plug and play install another one they're so similar (I've done it).  The computer doesn't even care.  If you run FWD all the time The Duty C does stay activated constantly so that could be argued as a downside, but that would be like arguing you should wax your car for improved aerodyanmics and gas mileage.  so far those that have done have noted zero issues. And electro-mechanically it's in an ideal environment - as near to a NASA clean room as an average consumer will get.   transmissions interiors are essentially closed systems that stay incredibly clean and the Duty C will maintain nearly consistent temperatures due to being submerged in fluid.  Electronics hate heat. 

Also turning electronic devices on and off can lead to premature failure (usually it's at such a small rate it's not noticeable but sometimes it is), due to the way the electrical loading happens at *on* and *off* moments. This is why bulbs frequently blow when they're turned on (or off).  Power conditioners can make light bulbs last much longer and provide better performance for anything that requires a signal..even devices (antennas, boosters, etc) in your own home. This might be minor, but so is trying to debate the efficacy of leaving the Duty C powered all the time verses cycling it over and over and over and over.