JOEK39 Posted May 14, 2004 Share Posted May 14, 2004 Hello: I've owned my 2001 Forester since new, no problems and get 21-23 mpg without fail. 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! Owner's manual says not to do this, but i pride myself on trying to understand the "why" in things. Knowing what I do about the all-wheel-drive system, i don't see what damage will be caused. With the fuse in, the center transfer case is disengaged and no power is applied to the rear wheels. Now the rear half shafts and drive shaft will still rotate with the rear wheels, but so what? The only reason that I can think of for SOA to discourage this is their #1 marketing strategy of "FULL TIME All Wheel Drive". The ability to put a Subaru into FWD ruins the FULL TIME part of that. I would appreciate the expertise and guidance of the group. I realize I am trading off the safety benefits and handling improvements that AWD gives you, but for 6-7 months per year I can save some $$. Your informed thoughts are solicited. Regards, Joe Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 14, 2004 Share Posted May 14, 2004 The reason they suggest you don't do this is it puts duty solenoid C into 100% duty mode. It'll overheat or wear out or something, I don't quite remember what goes wrong with it, but it certainly isn't good for the tranny. Quote Link to comment Share on other sites More sharing options...
benebob Posted May 15, 2004 Share Posted May 15, 2004 Yeah duty sol. c will cost ya about $600 to get replaced. That's a heck of a lot of gas. Quote Link to comment Share on other sites More sharing options...
avk Posted May 15, 2004 Share Posted May 15, 2004 But isn't keeping the solenoid in the open position much easier on it than constantly cycling on-off which is what TCU does to maintain the pressure? Just curious. Quote Link to comment Share on other sites More sharing options...
JOEK39 Posted May 15, 2004 Author Share Posted May 15, 2004 I'm also thinking now that if the "normal" AWD position is 10% (on or off?) thats not much different than 2WD position which is 0% (on or off). Keep the replies coming - I appreciate everyone's thoughts. Quote Link to comment Share on other sites More sharing options...
Llama Posted May 15, 2004 Share Posted May 15, 2004 it's true, it's not a 50-50 front/rear split in the AT. you're not going to save much gas with it in FWD mode, anyway. it's not like it's a 4WD spinning two axles. Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 16, 2004 Share Posted May 16, 2004 Like it said before it puts duty solenoid C into 100% mode, which is bad for it. Normal operation is 90% I believe, which would be when the split is 90/10. Also I think most the time it's not in normal operation. No it's not easier on the solenoid to leave it at 100% cycle, that'd be like saying, if you just inhale a lot of air and don't let it out it would be easier on your body, because you wouldn't have to stress your lungs. Obviously you'd die, and so will the solenoid. As benebob said, leave it in fwd mode, and you'll have to get it replaced. According to your mpg increase, and lets say you drive 10k miles a year, it would take you about 3 years just to break even with replacing it (which you WILL have to do if you keep running it in FWD mode) if it is ONLY 600 (I assume it's more) Quote Link to comment Share on other sites More sharing options...
avk Posted May 16, 2004 Share Posted May 16, 2004 No it's not easier on the solenoid to leave it at 100% cycle, that'd be like saying, if you just inhale a lot of air and don't let it out it would be easier on your body, because you wouldn't have to stress your lungs. Obviously you'd die, and so will the solenoid. Are you sure it's a valid comparison? One might think it's the electrical-thermal-mechanical cycling which actually wears out the solenoid and its valve. If there is constant current passing through the coil, with the valve open, there shouldn't really be any wear. Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 16, 2004 Share Posted May 16, 2004 I'm about 99% sure, but you can go ahead and keep a fuse in and well find out for sure when it burns out so we can all be 100% sure. Then you can replace it when it does. Sound good? Quote Link to comment Share on other sites More sharing options...
avk Posted May 16, 2004 Share Posted May 16, 2004 I'm about 99% sure, but you can go ahead and keep a fuse in and well find out for sure when it burns out so we can all be 100% sure. Then you can replace it when it does. Sound good? Let's try and keep this a technical argument. You seem to imply that the solenoid is not designed to withstand a continuous current even though it is designed to withstand a more stressful frequent on-off pulsing. If that's what you are 99% sure of, you probably have some first-hand information about how the system operates. Quote Link to comment Share on other sites More sharing options...
captainehh Posted May 17, 2004 Share Posted May 17, 2004 I'd just like to add a quick note and say that I've been driving my 97 Outback in FWD mode for over 50,000 miles due to a torque bind issue and things have been flawless. Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 17, 2004 Share Posted May 17, 2004 awd still works flawlessly? avk sorry if you felt I was not being technical but do whatever you want, i've provided the information that I know take it how you want. Quote Link to comment Share on other sites More sharing options...
avk Posted May 17, 2004 Share Posted May 17, 2004 THAWA: We know the owner's manual says not to have the AWD off for prolonged periods of time, so the benefit of doubt would go in favor of your point of view, and admittedly I have more questions than answers. I just thought that would help to get to the bottom of this. Quote Link to comment Share on other sites More sharing options...
friendly_jacek Posted May 17, 2004 Share Posted May 17, 2004 I'd just like to add a quick note and say that I've been driving my 97 Outback in FWD mode for over 50,000 miles due to a torque bind issue and things have been flawless. Yes, it makes sense to use this option when the the AWD is defective, but using FWD only in good system is an invitation for trouble. If this was so safe, why subary did not put a switch in the dashboard? Besides, do a search here, someone from Australia did this trick for several months and expierenced a failure. He posted a couple of weeks ago. Good luck with your experiment, keep us posted! Quote Link to comment Share on other sites More sharing options...
All_talk Posted May 17, 2004 Share Posted May 17, 2004 You seem to imply that the solenoid is not designed to withstand a continuous current even though it is designed to withstand a more stressful frequent on-off pulsing. While I don’t have any information specifically relating to the exact solenoid in question, in general it’s a heating issue. The off time gives the coil a chance to cool, if the solenoid isn’t designed to dissipate the heat of 100% on cycle it will burn out. The repeated mechanical cycling is what the solenoid is designed for and should handle it for a reasonable service life. Depending on how the coil is cooled (external-air or internal-oil), environmental and operating conditions could have an effect, which might explain why is has worked for some and others saw failure. Gary Quote Link to comment Share on other sites More sharing options...
avk Posted May 17, 2004 Share Posted May 17, 2004 On the picture in the service manual, it looks like the solenoid assembly has a sizable metal housing cooled by the fluid. But again, there's no detailed description of operation, such as the pulse frequency, coil resistance etc. Quote Link to comment Share on other sites More sharing options...
JOEK39 Posted May 17, 2004 Author Share Posted May 17, 2004 Yes, it makes sense to use this option when the the AWD is defective, but using FWD only in good system is an invitation for trouble. If this was so safe, why subary did not put a switch in the dashboard?... As I stated initially, the only reason I can see SOA not putting a switch on the dashboard, is because of their major marketing of FULL TIME all wheel drive. I've gone through a total of 4 tanks of gas now, continuing to average 28 mpg (vs 22 mpg before). At $2.10 per gallon, 12,000 miles per year, and 8 non-snow months, I will be saving approx $165/year in gas. I'm still not convinced its the smart thing, but I truly appreciate everyone contributing to this thread. For now, I'm sticking with 2WD mode. Thanks for the continuing dialogue. Quote Link to comment Share on other sites More sharing options...
friendly_jacek Posted May 17, 2004 Share Posted May 17, 2004 As I stated initially, the only reason I can see SOA not putting a switch on the dashboard, is because of their major marketing of FULL TIME all wheel drive. [.....] Thanks for the continuing dialogue. It is indeed a great discussion in this thread. As you might know, Subaru recently got its outback reclassified by EPA as light truck so they can comply with CAFE easier. Subaru got some bad press from tree huggers for that. If this switch was such a great idea, all AT subaru cars would have it and suddenly Subary would get an increased fleet fuel efficiency. Yet, it did not happen. As you say, marketing might be behind it, or engineering perhaps... Another anomaly: why would you get so much increase in total fuel efficiency (28 vs 22 mph). In theory, you went from 90/10 to 90/0 power ratio. I would expect no more than 10% improvement. What is your driving pattern: city vs hwy, average speeds and distances. Any changes recently? 22 mph sounds low for forester anyhow... I could try to duplicate this experiment in my 2000 legacy.... Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 18, 2004 Share Posted May 18, 2004 As I stated initially, the only reason I can see SOA not putting a switch on the dashboard, is because of their major marketing of FULL TIME all wheel drive. then please do explain why they even have the fuse there in the first place? and then explain why there's no switch/fuse/lever/etc in 5mt's Quote Link to comment Share on other sites More sharing options...
rude Posted May 18, 2004 Share Posted May 18, 2004 I also just want to add I've also been driving my 95 Legacy in FWD mode for 10,000’s miles due to a torque bind issue and things have been flawless. Furthermore, I HAVE added a nice FWD/AWD switch in the dashboard? Rude Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 18, 2004 Share Posted May 18, 2004 Another anomaly: why would you get so much increase in total fuel efficiency (28 vs 22 mph). In theory, you went from 90/10 to 90/0 power ratio. I would expect no more than 10% improvement. 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. Quote Link to comment Share on other sites More sharing options...
THAWA Posted May 18, 2004 Share Posted May 18, 2004 yet again I ask, is the AWD flawless, I don't mean do the rear wheels get power, I mean does it work 100% like it's supposed to? noone has seemed to say yes to this question. Quote Link to comment Share on other sites More sharing options...
JOEK39 Posted May 18, 2004 Author Share Posted May 18, 2004 re: 22 mpg seems low for AWD mode - - dealer reported this as within the normal range when I inquired about 2 months after purchase. I've never gotten anything other than 20-23 mpg since the car was new. Its mostly urban driving with few stops 14 miles each way to work on 2-lane roads 40-50 mph. I do make highway trips to my daughter's college often, 150 miles rt. I removed the crossbars from my roofrack to reduce windnoise, I love my moonroof and have it open 80% of the time 8months per year. I do tend to keep excess "stuff" in the back, so it may be 50 pounds overweight, and I weigh about 230. The mileage has been the same on the original Geolanders (piece of crap tire) as well as the current Uniroyal AquaGrips, although neither tire I would consider a "mileage" tire. I keep them well inflated, and use a 5W30 weight oil. I do tend to drive with a heavy foot, 70-75 mph on the highway. I am now REAL curious what other's who have tried this get from a mileage standpoint. Again, I appreciate everyone's thoughts. Quote Link to comment Share on other sites More sharing options...
JOEK39 Posted May 18, 2004 Author Share Posted May 18, 2004 yet again I ask, is the AWD flawless, I don't mean do the rear wheels get power, I mean does it work 100% like it's supposed to? noone has seemed to say yes to this question. In AWD mode, in snow conditions, I believe the AWD is working correctly, I can feel the power from the rear when needed, and I can tell I difference now in FWD mode in cornering. How else can I tell if it was working 100% in AWD mode ? Quote Link to comment Share on other sites More sharing options...
scottzg Posted May 18, 2004 Share Posted May 18, 2004 why does it get better mpg? You are still turning all that drivetrain via the rear wheels. Quote Link to comment Share on other sites More sharing options...
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