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Donut spare burns up differential

Can a small spare tire be safely used on an all-wheel drive vehicle? I don’t think so after driving my Subaru Outback less than 50 miles at under 50 mph and arriving at the service center with a totally burned up rear differential. Has anyone else had this happen? Should there be warnings about this?

A donut spare is a potential problem on any driven axle. Doesn’t your owner’s manual tell you to disable the AWD when using the spare? There used to be a fuse under the hood that you would insert to do this (or do you remove it-can’t remember).

Exactly! The Subaru Owner’s Manual tells you of the necessity of disengaging the AWD system when the donut spare is used, and it shows where to insert the fuse that is provided in order to convert the vehicle temporarily to FWD. When this procedure is followed, the damage that the OP described does not occur.

I just find it so sad that people do not read their Owner’s Manual. This is a very expensive example of what can happen when someone fails to read the manual, and since this type of situation constitutes owner negligence, this damage would not be covered by warranty–even on a brand new car.

Hopefully the OP will read the manual that comes with his or her next car, and hopefully he/she will not blame Subaru for his/her own negligence with this car.

It can absolutely happen. It can also happen in a non-AWD vehicle if you have a locker or limited-slip diff.

Reading the first couple of comments makes the average person want to scream. Tell me you all read the manual front to back. Who has read a computer manual. They are written in Greek. Some tell you what to do, but not where to go. Or you get instructions that say increase the tension to strengthen the arc. Greek language stuff. If you don’t know what the arc is, if you don’t know what item it is that is to be strengthened, and how to strengthen it…what good is the instruction manual. If McDonald’s has to put a warning label on their coffee cups, surley the auto mufacturers could put a warning label on the donut wheel. Who would know that risk with these new wheels. I just bought my first car that has the donut tire…so I am glad I read about this possibilitiy. I say there should have been a warning label if thousands of dollars of repairs can be incurred by improperly using the donut wheel.

I like that and agree with it.

I’ll say this, after reading all the woes and troubles on here from Subaru owners about their 4wd or awd or whatever it’s called system I can’t help but think in my mind, I don’t ever want to own a piece of trash like that. I can’t imagine a 4wd that can’t take a tire being half an inch taller than the other or the spare tire supplied with the car without burning out the axles. If their vehicles are that poorly engineered, they aren’t worth the steel and plastic it took to make it. What happens if you get one in a situation where it really needs 4wd like driving back on a logging road to pick up a downed deer and have a rain come up between then and now and have to actually wrestle the tinker toy back down the slick rutty road? My suggestion would be to trade that piece of junk for a Jeep.


Owners manuals are geared down to simple English and with dozens of warnings about this, that, and the other.
It is the owners responsibility to read the manual. Reading this manual, and comprehending it, should not take more than an hour at best and could be done in the evening of the day the car is purchased.

We had a gentleman who never, NOT ONE TIME, changed the oil on his new car. At about the 25k miles mark the engine blew up (not even rebuildable) due to oil sludge.
Whose fault is this? Ours, according to the owner because we never told him he had to change the oil.
Maybe this particular warning could be tattooed on each forearm to prevent future problems like this.

Read your owners manual and note all of the warning disclaimers. Now, picture your car with all of those warning stickers plastered all over it.

As a tech, the first thing I do on a repair I’m not familiar with is go to the book. This applies to anything else I do in life that I’m not familiar with. As a licensed aircraft mechanic the first thing that must be done when performing an aircraft repair is read through the ADs as they’re called (airworthiness directives). This is required.


Actually, yes, I DO read the Owner’s Manual for a car from cover to cover as soon as possible after I buy a car, simply because I know that it could be costly, both in terms of dollars and in terms of human safety, if I do not read this information. And, I periodically review certain sections, just to be sure that I don’t screw something up.

Do I read a computer manual from cover to cover? No. The reason for not doing so is that my computer does not have the potential to strand me on a country road, at night, if I fail to read the manual. My computer will not lead to huge repair costs if I do not read the manual. Nobody’s life could possibly be in danger if I fail to read the manual for my computer. And, my computer does not need to be maintained in the same fashion as a car.

I will agree with you that computer manuals are frequently written in a manner that is not readily comprehended by a non computer- savvy person. However, the Owner’s Manual for a car really is written so that someone with an 8th grade education can comprehend it. If you are implying that people do not read car Owner’s Manuals because they are too complex, then there are only two possibilities–either you have never read one, or…never mind, I won’t say it.

While it might be a good idea for manufacturers to put that warning on a donut spare tire, the fact remains that there is a wealth of information on a myriad of topics in a car Owner’s Manual, and failure to read it and to follow it can result in HUGE repair costs and can lead to endangering the lives of both the driver and the passengers. A car is usually the second biggest cost that people incur in their normal lives, whereas computers are now considered to be almost in the category of appliances because they now cost so little and are replaced so frequently.

Do most people read computer manuals? Probably not, but their ultimate cost penalty for not doing so is relatively minor. Do people read car Owner’s Manuals? Apparently few people read these either, but invariably the non-readers come to regret that oversight when they wind up paying large sums of money to correct their failure to read. Therein lies the essential difference between a car manual and a computer manual.

Any other questions??

  1. Is this an automatic transmission or manual transmission?

  2. Have you always run sets of 4 matched tires in make/model/brand/wear? If not, running this spare maybe through it over the edge that is all.

I suppose that is why full time AWD vehicles, eg Toyota’s, come with full sized spares.

NOT THE FACTORY SPARE,its the radius that counts, NOT THE WIDTH,

so my answer is NO WAY.

NO WAY what?

No way a donut spare can ruin a Subaru differential?

You’ve never owned a Subaru, have you?

Installing the donut spare without first disabling the AWD system on an automatic-transmission Subaru is a prescription for disaster, and, yes, 50 miles is more than enough to tear up a differential or the AWD transfer clutch.

As we all love to say, “RTFM,” which translates, loosely, as “Read The #$*&^%$ Manual.”

Have a nice day.

NEVER HAPPEN as I said,owned 1 of those POS. say the word diameter.

the manf. would never give you a spare thAt would damage their own car.

and as I said 1 Subaru is enough, POS!


Except that, if the tires on the four regular wheels weren’t relatively new to begin with, the spare (having not been used) would probably have a slightly larger diameter. That, or it was underinflated thus reducing the rolling radius.

I seriously doubt anyone is gonna take their subaru into the back woods like you are suggesting. I’ve driven in snow and even a few muddy driveways in my Civic. IF I ever need A/4WD, it’s a call off day for work. The picky AWD system is why I’ve ruled out Subaru altogether from my future car purchases.

I agree with budd2049 about an underinflated spare. How many people on the planet ever bother to check the tire pressure on a T-type spare? And especially considering the fact that many of them require 60 or so PSI.

Guess there ought to be a warning label on the windshield about that also.

Agreed; what about a warning that the car won’t run without gas in the tank? Might as well…those darn owners manuals are so hard to understand!

(although, with all the octane questions on this forum I guess the fuel warning isn’t such a stretch…)

Owners manuals are geared down to simple English and with dozens of warnings about this, that, and the other.
It is the owners responsibility to read the manual. Reading this manual, and comprehending it, should not take more than an hour at best and could be done in the evening of the day the car is purchased.

And it should be reread in a couple of weeks and again in a couple of months.

They can cram that manual where the sun doesn’t shine.

I’m not going to sit on the side of the road somewhere with a flat tire and pull out reading material. Chances are it’s pouring the rain and I’m headed somewhere I got to be anyhow. Any dingle dork ought to be able to change the spare tire onto a car without reading a 400 page manual on how to do it. The worst thing is firguing out that screwball jack that comes with the car and where did they put the lug wrench.

If Subaru can’t put a spare tire in their vehicle that can safely operate with their vehicle and IMO, if they can’t make a 4 wd that can take a little abuse and not be such a puss, then I’d get rid of that pile of junk and get a Jeep or Chevy or Toyota or someone else’s vehicle. If you’ve got a 4wd that’s going to fall apart on no more of a deal than that, you a. have no real use for a 4wd because the one you have is useless and b. if you really needed 4wd, that sorry overly tire sensitive vehicle ain’t gonna cut it.


Tell us how you really feel, Skip. ;0}

Current Subaru owners: Are there warning stickers on the spare or jack compartment instructing you to disable the AWD when using the spare, or is this info just in the owner’s manual?