it's only bad if you are pushing the engine along in gear. Supposedly isn't good for the catalytic converter. I'm not sure if that is just urban legend but I don't do it anyways. Back in my younger days we used to play kill switch games with our motorcycles, not very smart but it was amusing.
Probably not the best of practice in a car anyways sinnce you lose power steering and braking.
I'd buy this if the car was carb'd.
It will slightly increase wear on the rings and cylinder walls as the unburned fuel taken into the cylinder will "wash" the oil coating from the cylinder walls and rings. The dry start does increase wear.
I do not think this claim is valid for several reasons.
1) With a fuel injection system (assuming modern-ish car) there isn't a whole ton of fuel to be sucked in. Yes, there is some, but it's less (much less?) than the fuel sucked in during an intake stroke.
2) Most of the fuel that will be drawn in I think (in my semi-professional opinion) will be gaseous, not liquid, because everything (valves, piston, cylinder walls, intake manifold) will be very hot. It is difficult for a gas to be a good solvent and "wash" away the oil.
3) An engine under normal operating conditions will see the same "washing" effect during intake and compression stroke in addition to having the oil burned off during the combustion and exhaust strokes. I cannot believe that a little fuel will dispose of more oil than the heat from a combustion cycle.
4) Pistons and piston rings are designed to carry fresh oil up with them on every up-stroke and recover as much oil as possible (so it is not burned) on every down stroke. Whatever small fraction of oil is left on the cylinder walls does help, a little, but is certainly not required nor always present because it is burned off in 2 of every 4 engine cycles (see 3).
5) Assuming some fuel does manage to put the oil into solution, the oil doesn't magically disappear, nor can I imagine it flowing very far in the short amount of time available. That is to say the oil may be in solution with fuel, but it will still be present and able to partly, or fully, lubricate the piston as it would (or would not) have done in normal operation.
No. There is nothing you can do to an engine or drivetrain, excluding mechanically over revving down a hill, that is worse than the stress of normal operation when its running under its own power and containing thousands of explosions several times per second at hundreds of degrees at thousands of RPM every single day.
^^This.
To expand: the oil pump is still turning, most importantly, so no big deal on engine wear.
