As a matter of fact...
I had a failed experiment last month regarding suds in the motor of a Bissell. My mom was given a Bissell QuickSteamer Plus last month from a friend of hers, who stated that occasionally, the soap doesn't come out.
I went over there to try and resolve that problem. I removed the nozzle, brush and spray bar, then washed those parts out. The nozzle was clogged with dog hair, which was most likely the cause of the machine not spraying.
Next, I filled up the solution tank with nothing but hot water and gave the machine a quick test run. While the suction was good, there was some water spitting out of the vent on top of the dirty water tank, and I thought nothing of it.
However, during the middle of cleaning another section of carpet, the motor suddenly made a HORRIBLE noise and I immediately shut the machine off. Turns out that water got sucked into the motor! I didn't want to turn the machine back on again after that. I think that happened because I squeezed the trigger while going forward AND reverse. Perhaps next time with this machine, I should squeeze the trigger ONLY on the forward stroke.
On the other hand, I have owned a Lift-Off Deep Cleaner since 2012, and it's still going strong. Even though this machine features a hot water heater for the upright portion, the heater has never failed on me.