In an informative answer suggesting that wheel bearings could be the cause for road drone/hum noise, no mention was made of heat.

In another nice answer I learned that bad/noisy bearings generate their own heat.

If noisy bearings generate their own heat, can we not determine whether bearings are the issue, and which wheel it is, by simply touching the rim after a bit of driving?

With disk brakes, even a very slight snug disk generates so much heat that a short trip means the rim is so hot one burns one's fingers if one touches it.

Do failing wheel bearings generally generate heat substantial enough that one would feel it with one's hand? Even a little bit of heat means that there would be a basic test for determining not just that wheel bearings are indeed the issue, but also which wheel it is.

  • I wouldn't expect a grumbly wheel bearing to produce enough heat to distinguish between other heat sources. Brakes are designed to create friction, bearings have the opposite purpose, even when they're going bad they're still mostly doing that job. – GdD Jul 24 '17 at 9:09
  • Related and funny: When a train bearing is seized it get's called a "hot box", it produces the following issues: abload.de/img/dsc03470t8ube.jpg – Martin Jul 24 '17 at 9:21
  • @Myself: So you're saying that when wheel bearings do seize, they generate a ton of heat. GdD: you're saying the bearings could be faulty but yield no noticeable heat. Do the two pieces of information together constitute the answer then? – Calaf Jul 24 '17 at 9:51
  • @Myself wait.. I see now. These sparks underneath the train are not the result of the heat from the bearings. They are from dragging a wheel that has seized along by the inertia of the train. In other words, wheel bearings do not generate much heat. They just eventually seize (and then of course also with no heat generated from themselves). – Calaf Jul 24 '17 at 9:54
  • @Calaf At no point I wrote that there is no heat. The sparks in the photo is an disintegrating bearing (or a seized brake) – Martin Jul 24 '17 at 10:11

Bad bearings CAN produce heat, depending on the exact bearing failure it could under circumstances also produce very significant heat (in extreme cases they could get so hot that the grease is burning) but that is no effective indicator since fluctuations of pad brake pad pressure/effectiveness and other factors can also produce heat. Under circumstances a bad bearing can produce significantly less heat than the mentioned brake fluctuations.

The most effective diagnosis would be the following:

  • Jack up the entire front/rear
  • Rock the tires and feel for play (not so strong that the car is falling from the jacks)
  • Push back the brakes and listen/feel at the wheel hubs while turning them by hand.

Indications for a failed bearing would be feel-able play, unusual sounds or a significant resistance while turning

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    Probably best to ensure the use of axle stands is mentioned, they should make the car much more stable when working on it. Ideally do both sides of the same end of the car to keep it level. – Mauro Jul 24 '17 at 15:38

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