Cause of burning smell from R front tire only on AWD Subaru

Maintenance/Repairs
1

Hi All, sincerely appreciate your help narrowing down the cause of this.

Friday after a 45 minute highway ride in our 2003 Subaru Outback 3L H6 VDC I noticed a burnt smell which smelled much stronger than the typical hot tire smell. When I checked around and under the car, I traced the smell to the front right tire/tire well. I could not find any evidence the tire was chafing against anything, or any evidence of any fluid leaking in the tire well or in the engine block on that side of the tire. The smell is stronger and more pungent than the typical hot tire smell.

Would could the source be? Car is in great shape, we have a great mechanic - honest, sharp and a good value, but before doing the rounds of mechanic, tire rotation place and alignment place (all 3 different locations), would be nice to be able to narrow it down.

Some things I’ve thought of:

  1. Leaking fluid that I’m not able to see which is falling on a hot part in the right side of the engine block close to that tire

  2. Problem with brake fluid and brake pads causing the brake bads to close up much harder on the right front wheel

  3. Brake fluid leaking near the brake pads in the right front tire well

  4. Tire alignment issue (Though I had the tires aligned about a year ago, probably a good idea to do again now - manufacture says it’s unnecessary to do frequently but on an AWD vehicle I think it should be done once every 6 mo. to 1 year. However, on on a previous alignment after a tire rotation when a front wheel was off alignment there was no smell like this).

  5. Tire rotation - I’m a little past due but not much, but don’t understand why the R tire alone would act up, and before previous rotation never had a smell like this.

2

THE NEXT SEVERAL CAUSES WERE SUGGESTED BY FELLOW MEMBERS ON ANOTHER CAR FORUM:

  1. Wheel bearing symptoms, which are similar to 1) 2) and 4) above

  2. Stuck brake caliper - the slide pins are probably rusted so the caliper can not move away from the rotor. Pretty common problem.

  3. The caliper piston is jammed.

  4. The rubber brake hose has deteriorated and has blocked the return of fluid from the caliper back into the line.

3

4, 5, 9, no.

2 should be reworded to match 7, which is pretty much the same thing as 8, and would be the first thing I’d suspect.

3 probably not unless you’re noticing the pedal getting squishy.

1 is possible, but generally you’d smell that in the middle of the engine area too, not just at the passenger tire.

4

Thanks Shadowfax. Member of another car forum also suggested the CV (Constant Velocity) Boot. “If it splits it slings grease onto the exhaust. Which smells awesome. And the passenger side is the more common side to fail.”

5

wheel bearings would be the most likely cause. most roads are crowned from left to right for water drainage,and right turns are more common than left turns. all this puts more stress on the right wheel bearings. the binding brake caliper could also be the problem, this can cause excessive heat buildup on the brake disc rotor that will travel to the tires. you could also have a torn halfshaft boot at the front cv joints. the cv joints are like ball joints packed with grease. if the boots have a hole or thorn the grease will spray out with centrifugal force, possibly onto the hot engine.

6

The first thing to do is to rule out a sticking brake caliper and a wheel bearing that is going dry. Have you (carefully) felt the temperature of that wheel, following a high-speed run?

If you can rule out a sticking caliper and/or a bad wheel bearing, I think the most likely suspect would be a leaking CV boot. The one for the right front wheel is almost directly over the exhaust pipe.

7

To elaborate on what VDCdriver is saying, after a long drive, see (carefully) if that wheel is hotter than the others.