Join the Car Talk Community!

Discussion Rules

Welcome to the Car Talk Community!

Want to ask a question or join the discussion? Great! Join now.

Sign In Register

The real problem with the Subaru Outback's burning smell

edited November -1 in The Show
The problem with the caller from CA's Subaru smelling like burnt rubber is the actual tires are heating up due to an improper torque split between the tires.



Subarus are very sensitive to changes in tire pressure and thus the diameter and will wear the tires down. The driver mentioned 8 sets of tires. He has a bad torque split in the AWD system.
«1

Comments

  • edited February 2011
    I think it is more likely that a torn CV boot is causing grease to leak onto the exhaust manifold or exhaust pipe. The proximity of the CV joint to the tire could cause someone to think that the smell is coming from the adjacent tire.

    Truthfully, I'm rather surprised that the brothers did not think of this problem that is not uncommon on older Subarus.
  • edited February 2011
    Two clues: Both several sets of tires, AND I think caller stated a 1997 Subaru with 46,000 miles. That's not a lot of miles for 13-14 years, which makes the tire wearing even more dramatic. (Could there be some wheel / axle / differential problem that is slightly dragging the tires and wearing them out? Would problem be worse not if temperature is warm or hot, nor if drive is uphill or downhill .. but if drive involves lots of sharp turns, and thus more dragging of the tires?)

    Maybe problem is similar to something I had with my car. I had a low-mileage 1996 subaru legacy, with infrequent / occasional burning smell -- it usually only happened after a long drive. My problem was never solved. But mechanic suspected it was connected to car not being driven sometimes for days (I work from home). Thought was an old car sits for days; rust or other sticking problem forms on some part of wheel or axle or brake caliper; then a long drive, extra friction eventually generates excessive heat.

    I, too, only smelled the burning smell when I got out of the car -- smell was near one of the front wheels, but that's also near the axles, and cv joints and engine, and ...etc
  • edited February 2011
    I agree its the tires, but there could be several reasons for the smell and tire wear. First is alignment. Since the car is AWD, this doesn't seem like it would be as much of a problem as a FWD vehicle would have.

    When the car is going uphill and when ever it is accelerating, the front tires are pulling ahead of the vehicle, so it tends to toe in the tires. During deceleration or downhill, the tires want to toe out. The alignment specs are meant for average driving, but if this vehicle sees more acceleration then deceleration, the specs may need to be modified for a little more toe out. A good tech should be able to figure out how much based on the wear patterns of the tires.

    If the wear pattern is even, it may be that he is getting about equal wear going up and down hill, but there is excessive toe in and out due to his driving patterns. The answer would be to limit the fore and aft movement of the wheels by using a harder durometer rubber. Depending on the front suspension design, it could be trailing arm bushings, control arm bushings or sway-bar bushings.

    He could also be experiencing wheel hop while going uphill. Again he may need a harder rubber in the above bushings or in the motor mounts. If its wheel hop, I would look into the motor mounts first. Start with the mount farthest from the center of rotation of the engine. Normally that would be the torque arm or dogbone. It could be the front mount on some engines. This would also aggravate the torque split issue.
  • edited February 2011
    I agree that he has a problem with alignment or torque balancing eating the tires and that could be the cause of the burning smell. However, I too have a 97 outback (manual transmission) that does the same thing, minus the eating of tires. I get many years out of a set of tires. Also, I replaced both front axles last year so there are no leaking boots and had the front end completely gone through after that. I also cleaned the engine after doing all the work.

    I too get the burning rubber smell after pulling a hill and stranger yet, it only happens when its cold (as was alluded to) and never in the summer time. It did it again last week during a cold snap after pulling a hill to a friend?s house. I have popped the hood and the smell is much stronger under the hood and obviously is not coming from the catalytic converter. The belts look to be fine and there is never any squealing so I doubt they are the problem (but I can?t totally rule out the possibility). Being that I don?t pull many hills where I live I have yet to nail this one down.

    Thought I?d throw that little curve ball into the mix.
  • edited February 2011
    I don't know if the Subaru has a carrier barring, but if it does, I think its that. The drive shaft angle is changing long enough and steep enough that it's stressing the rubber in the carrier. Edit: Bunch of people with a similar problem http://tinyurl.com/5w6hqx2
  • edited February 2011
    Thanks for the info! I'm starting to lean towards the AC belt slipping. My lady has been driving the car lately and said that its happened a couple times while on the flats as well. The key thing is that it has to be cold (really cold) to happen. Since I can manually control the AC pump I use it sparingly during defrost but I haven't paid attention to its setting when the smell occurs. Its my guess that when its cold enough the belt may be slipping a bit when the AC kicks in thus causing the smell.

    I'll know this summer if its the carrier bearing. The transmission has been making noise while idling in neutral so its about time to do a rebuild. I got the car from a friend who drove it very hard. I swore that I wouldn't buy it from him when it came time to sell but he made me an offer I couldn't refuse:). At least I've had several good years before getting to this point.
  • edited February 2011
    Listening to this I had a "Huh, my car does that, too." Except mine's a 2003 Forester. None of the tire wear issues, or the only-uphill, but still a burning smell that I cannot locate (no leaking fluids, no obvious smoke, though it started only after I had the engine replaced). I think the heat from the catalytic converter explanation fits my situation best.
  • edited February 2011
    I have the same problem with my 2005 Subary Legacy (same thing as the Outback, but with different suspension). I'd stop the car after driving on they highway, then smell something like burning rubber once I got out of the car. I couldn't see any leaking fluids, but I sniffed carefully around the engine and found the smell coming from around the turbo/exhaust pipe - which makes sense because that's it's hot enough to burn things.

    The local Subaru dealer identified a leak from the front differential, which was dripping on to the exhaust. We're working to find the source of the leak, but once this is fixed, I expect it will solve the problem.

    I suspect that differential fluid smells more like rubber when it burns. It's not motor oil, so it doesn't smell like motor oil when it burns.

    Regarding the theories about tires, I have to say that's not the problem I have. My tire wear has been consistent with the expected life of the tires, and the smell is clearly not coming from the tires. I suspect the caller's problem with replacing tires was improper inflation -- unrelated to the smell.
  • edited February 2011
    in case it might help (although you think your problem is differential fluid, not brake fluid):
    My 96 subaru had a very small leak of brake fluid. Location was at a connector that joined two pre-formed brake lines. The connectors were located in the engine compartment, I think somewhere near the engine wall over the right front tire area. When it dripped, drips landed on part of the exhaust system below.

    Note that a minor brake leak might only occur when you press on the brakes hard enough to raise brake line pressure -- say when you slow down rapidly on a highway off ramp. So a leak might be intermittent, depending on your use of the brakes.
  • edited February 2011
    I have experienced this symptom many times here in the White Mountains of NH (including yesterday). It occurs after I go up a long steep hill with snow tires, especially when there is some slippage on the way up, get out of the truck and smell burning rubber. It doesn't happen in extremely cold conditions, but more when the temp. is in the high twenties and up.

    I wonder if Stan has snow tires or some extra-soft all season tires.
This discussion has been closed.