If I select at my dish washer:

  • A fixed-time program, it displays 2:20 in the beginning and it runs for exactly 2:20
  • An auto program, it displays 2:45 and runs for 2:15 to 2:45 so difference is < 20%

The variation is never in plus meaning that it never runs longer than initial display time.

If I select at my washing machine:

  • A cotton program, it displays 4:20 at the start then goes to 2:36 after 10 minutes, but actually can wash between 2:00 and 4:00
  • A silk program, it displays 3:35 in the beginning then varies with values, but runs for 1:00 to 5:00 hours.

The variation is many times in plus. The most weird scenario was when it showed 2:00 at 8 pm, but ended its whole cycle at... 2 am meaning that it run for four more hours than predicted.

The above was checked / tested / confirmed on many nowadays and modern dishwashers and washing machines, from many suppliers, including Bosch, Candy, Beko, Whirlpool and many more.

What am I missing? Why modern devices of a one kind can predict running time with the precision to 5-10 minutes while devices of other kind have variations to up to 200-300%? Especially given the fact that boths kinds of devices are doing pretty much the same, i.e. using water and cleaning agent for washing either dishes or clothing.

  • 2
    My guess is that it's a matter of cost. They surely could tell you the exact time for your clothes washer but it probably wouldn't be a selling feature... you turn on the washer and go about your business. Whereas with the dishwasher, one might be waiting for it to finish to reuse them or put away the dishes and finish up cleaning the kitchen.
    – JACK
    Jun 15 at 12:14
  • 2
    It may be that the initial time is based on a presumption of incoming water temp & pressure. If the actual temp & pressure are different from expected, it will take longer to fill the tub and heat the water (if that's done) or wash longer to compensate for lower temp. Remember that there's significantly more water going into the clothes washer than there is the dish washer and that the clothes washer fills & drains more times than the dish washer does, therefore these items have a greater impact on overall run time. </wild guess>
    – FreeMan
    Jun 15 at 13:02
  • 1
    @FreeMan that's part of it, but the old part. Generally only the main wash is heated, and possibly one rinse (for all but ancient machines) and filling + heating is a small part of the total time. I can confirm variability with a cold cycle and consistent pressure.
    – Chris H
    Jun 15 at 13:10
  • @JACK, see my answer below. They actually couldn't predict the time accurately. To have an accurate time means either wasting lots of water, energy, and/or time (to deal with the worst case) or risking dirty clothes (assuming the best case). You can also interrupt the dishwasher trivially, which you can't do with the washing machine. I often abort the dishwasher programme partway into the drying cycle, and open it if I'm in a hurry (in summer the kitchen is well ventilated and in winter I have a dehumidifier in there, so I'm not worried about steam)
    – Chris H
    Jun 15 at 13:13
  • 1
    @ChrisH We put a man on the moon and brought him back..... I really think they could predict the time to do laundry if they really wanted to. :-)
    – JACK
    Jun 15 at 15:03

Old washing machines used to do everything to time (except heating the water, but that's a small part of the cycle and still reasonably predictable), so would always be pretty close. Newer ones measure all sorts of things, from the weight of clothes to the dirtiness of the water. What they do with that data is unfortunately proprietary. The time can go up if the machine decides an extra rinse is needed, for example. Extra soaking time may also be added - and this can be quite a lot. A fuller (heavier) load can mean more water, which may take time to heat. They also measure vibration, and if the drum starts to vibrate excessively as it spins up, they'll run slowly for a while to redistribute the load, perhaps more than once.

Dishwashers can and do use similar turbidity sensors. They can still use extra water, which adds to the heating time, except that the wash usually starts cold and warms up as it goes. They of course don't have to shake the contents about before spinning.

In a sense the washing machine always uses an auto programme, but doesn't tell you that. The user experience management is done better on the dishwasher auto program, by giving the worst case estimate.

The biggest issue is the use of a fairly precise time. A progress bar would make more sense in many ways, as it's not like you can plan for when they finish anyway and no one trusts progress bars.

  • 3
    Fundamentally, it's much because dishes basically get clean in an unambiguous way, while clothes can continue to give off "stuff," which could be dirt, dye, lint, etc. and it's really not possible to say with accuracy when the clothes are clean enough for your satisfaction. Jun 15 at 19:12
  • @CarlWitthoft that's a good way of thinking of it
    – Chris H
    Jun 15 at 21:09
  • Chris & Carl, I wouldn't think about the whole thing this way, so thank you. Perfect answer (and comment).
    – trejder
    Jun 16 at 13:53

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