How to get better MPG on a Subaru, FWD fuse, winter mode, etc.

[slacktide_bitog]

1998 Forester, EJ25D (DOHC), automatic

Subaru is known for poor gas mileage due to the thirsty AWD. Most of the automatic transmission models have a slot for a fuse to disable AWD. It is primarily intended for when you use a spare tire or if the car needs to be towed, but it can also result in better gas mileage.

Some people say you can use the FWD fuse all the time with no problem, and others say it's for emergency use only and that damage will occur in only a few miles

The automatic transmission has PRND321, where 2 is only 2 (not 1 and 2 like most Japanese autos are). 3 is 1/2/3 (like D but with OD off). Subaru says you can start in 2 for better winter performance, and I have seen winter modes on automatics that make it start in second. Is it safe to do this all the time? That may help with better mpg.

I plan on changing the ATF using the popular Maxlife. Too bad nobody makes a 50w60 gear oil or something lighter. What is the lightest GL5 out there?

 

[supton]

IMO, I'd let it start in 1st. Starting in 2nd is going to have the torque convertor slipping "a lot" and creating heat. Heat that which must be radiated out through the cooler is heat that isn't used to move the car... to me, it means wasted energy. That said, in cold weather this might be the trick to get it to warm up faster, assuming you don't need to accelerate fast. Just quit doing it once the engine is up to temperature.

Can't comment on the rest of it, other than to ask, just how much mpg do you need to make up? I mean, if your commute is all of 5 miles, do you really need to hit 50 mpg in order to keep fuel costs low?

Isn't the "transfer case" (whatever is between the transaxle and rear driveshaft) some sort of viscous coupling? I can't see how having the fuse pulled for a long time would damage anything. Everything would still be rotating, there just wouldn't be any drag between the driveshafts. But I am not familiar with the guts of these things--just a wild guess--but I don't see how long term usage would damage it, having the rear axle disabled.

I'd think better mpg could be had through LRR tires (once new tires are required), low cruising speed and trying to coast to stops (without annoying other drivers).

 

[nascarnation]

You're driving a 20+ year old rig so you've already saved the big cost: depreciation.
At two bucks a gallon, any improvements you make hardly seem worth the trouble.

 

[geeman789]

Make sure the little things are all done ...

Clean air filter.
Fresh spark plugs.
Synthetic oil in the diff's.
Pump up the tires above Subaru's recommended pressure.

Drive it like fuel is $ 10.00 a gallon ... accelerate smoothly, lower speed a bit on highways, coast whenever possible. Don't idle excessively.

But at the end of the day, if fuel economy is your main concern, you are driving the wrong car.

 

[Surestick]

Originally Posted by supton
IMO, I'd let it start in 1st. Starting in 2nd is going to have the torque convertor slipping "a lot" and creating heat. Heat that which must be radiated out through the cooler is heat that isn't used to move the car... to me, it means wasted energy. That said, in cold weather this might be the trick to get it to warm up faster, assuming you don't need to accelerate fast. Just quit doing it once the engine is up to temperature.

Can't comment on the rest of it, other than to ask, just how much mpg do you need to make up? I mean, if your commute is all of 5 miles, do you really need to hit 50 mpg in order to keep fuel costs low?

Isn't the "transfer case" (whatever is between the transaxle and rear driveshaft) some sort of viscous coupling? I can't see how having the fuse pulled for a long time would damage anything. Everything would still be rotating, there just wouldn't be any drag between the driveshafts. But I am not familiar with the guts of these things--just a wild guess--but I don't see how long term usage would damage it, having the rear axle disabled.

I'd think better mpg could be had through LRR tires (once new tires are required), low cruising speed and trying to coast to stops (without annoying other drivers).


I think the viscous center differential is on manual drivetrains.
The automatics had an electrically controlled clutch in the center diff (hence the fuse you can pull to disable it, no fuse for the purely mechanical viscous diff).

 

[supton]

Originally Posted by Surestick
Originally Posted by supton
IMO, I'd let it start in 1st. Starting in 2nd is going to have the torque convertor slipping "a lot" and creating heat. Heat that which must be radiated out through the cooler is heat that isn't used to move the car... to me, it means wasted energy. That said, in cold weather this might be the trick to get it to warm up faster, assuming you don't need to accelerate fast. Just quit doing it once the engine is up to temperature.

Can't comment on the rest of it, other than to ask, just how much mpg do you need to make up? I mean, if your commute is all of 5 miles, do you really need to hit 50 mpg in order to keep fuel costs low?

Isn't the "transfer case" (whatever is between the transaxle and rear driveshaft) some sort of viscous coupling? I can't see how having the fuse pulled for a long time would damage anything. Everything would still be rotating, there just wouldn't be any drag between the driveshafts. But I am not familiar with the guts of these things--just a wild guess--but I don't see how long term usage would damage it, having the rear axle disabled.

I'd think better mpg could be had through LRR tires (once new tires are required), low cruising speed and trying to coast to stops (without annoying other drivers).


I think the viscous center differential is on manual drivetrains.
The automatics had an electrically controlled clutch in the center diff (hence the fuse you can pull to disable it, no fuse for the purely mechanical viscous diff).


Ah, that makes sense. I think the RAV4 (and others like it) did likewise. Probably PWM on the clutch so as to modulate torque being sent to the rear wheels.

 

[heynow]

Even when not in AWD mode, you're still spinning the AWD components... 4 axles, 2 differentials. The only real way to gain any significant mpg would be to remove these. I would just run it as is.

 

[Pelican]

Buy yourself an eye dropper for you'll need it to measure the savings in fuel.

 

[zzyzzx]

Sell it and get a small front wheel drive car.

 

[supton]

I dunno--is it wrong to strive for the best mpg regardless of what vehicle one drives? Does it hurt to ask? For all the OP knows, a couple of low-buck mods might reap dividends. And maybe the OP "needs" Subaru AWD for winter (plans to reinstall the fuse when it's snowing, perhaps).

Quick look on fuelly shows 23-24 mpg for 1998 Subaru. Low but I'm not sure swapping vehicles would have a payback (one has to run the math to find out, and I don't know the particulars for the OP).

OP, I think one of the better tools is to get a Scanguage (or similar, maybe use Torq on your phone) to monitor instantaneous mpg. And to track mpg on a daily basis. You may find that driving at 60 mph yields better mpg than 50 -- if you let your speed droop a bit while climbing hills, the extra momentum at the bottom might help you stay in top gear the whole way. OTOH you might find in your flat region that cruising at 45-50 yields the highest daily / trip mpg. Won't know until you measure, and w/o such a tool you are stuck waiting for each tank of gas to go by.

Although, now that I think about it, is this the era of problematic head gaskets?

 

[Andrew1972]

It is rated at 21/28 MPG EPA which is similar to its limited competition of time like Toyota RAV4 and latter Ford Escape etc. Subaru is not poor for then vs competition but as time progressed they did not improve while competition did. That all got reset when they switched from automatic to CVT.

Pull the fuse and see what transpires. My guess is 0-1MPG savings.

 

[fdcg27]

There is nothing you can do to make this thing an economical vehicle.
Shutting off the AWD is intended to accommodate differences in tire sizes and nothing more. It will not make this thing into a Yaris. Anyway, if you don't need AWD, then why even have a Forester?
You want better fuel economy?
Then buy a more economical car.
You want better fuel economy in a Subie?
Then buy a later generation that delivers it.
Our '17 Forster is actually more economical than our '12 Accord driven by the same person (my wife) under the same conditions.
The '09 Forester has been a bit of a gas pig since new but it does offer plenty of room, a very soft ride and excellent AWD.
Drive gently to maximize fuel economy. There's really nothing else you can do.

 

[E365]

70w-80 is the lightest GL-5 I've seen. MOPAR Full Synthetic is one of the cheapest in that grade. Part 68227765AB