Automatics changing my view.

[dkjones96]

Originally Posted by Scott

Shifting to neutral at lights I believe is a gas saver, I once heard that to generate the 500 psi oil pressure required by an automatic, takes 15 to 20 hp, that relates directly into mpg and waste sitting at a light.

That just HAS to be an exaggeration. I can't (and won't) believe for a second that the engine has to create anywhere near 15-20 more hp if the car is in gear vs neutral.

In fact, if I remember correctly from my data logging on Tracker, calculated load was mostly unaffected(+-1%) by neutral vs drive. However, turning on the a/c yielded a 15% increase in calculated load.

Also remember that automatic transmissions do not disengage the hydraulic pump when it is in neutral. There are plenty that do in park, but not neutral so you are still having to create pressure. (That's why you can neutral coast in automatic cars but not all of them can EOC) My old Cressida did disconnect the hydraulic pump in park and if you revved the engine up and switch between neutral and park you could hear the difference... barely.

Just to clarify on pressure requirements I'm going to take numbers from my factory service manual for the Tracker.

Line pressure at engine idle:
Reverse range - 79-86psi
Drive range - 53-58psi

Line pressure at TC stall speed:
Reverse range - 188-233psi
Drive range - 136-156psi