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Hey all. I have a 1997 Toyota Celica AT and am looking to improve its overall FE. My question is...will my transmission be affected from P&G? I usually only shift into neutral if my speed is lower than 40mph. Will this still cause transmission wear? Thanks

Welcome, AJ1218!! We are glad you decided to stop by and ask questions. :)

You are perfectly safe shifting into neutral at any speed. The potential problem arises when you try to shift it back into drive. ;)

The correct (and safe for your transmission) way to do this is referred to as "rev matching" and eliminates the possibility of damage to your vehicle.

The basic idea for this is that your engine turns at a particular RPM for a particular speed of the car (MPH). You need to know what this RPM is for any given speed (I recommend learning the RPMs for every 10mph mark) so that you can apply the throttle GENTLY to raise the RPMs to the level they should be while you are still in neutral, then shift back into drive.

For example, suppose I shift into neutral at 60mph so that I can coast. Suppose also that I want to reengage the transmission at 50mph. I know that for my car the RPMs should be about 2k or so for 50mph so when I get to that speed, I give the engine gas until it is about 2k RPM and then engage the transmission. There should be no jolts -- it should be very smooth. That is when I know that I've done it correctly.

To get the right feel for this, try rev'ing the engine while you are parked to particular RPM levels. It takes very little pressure when you don't have the engine loaded (such as when you are actually driving).

If you do not have a tachometer you can still do the same general action by listening to the sound of the engine and remembering what that sound is for different RPMs.

I hope that this helps?

Yes this helps a lot! :) I do have a tachometer and I often reengage into drive at around 35mph. When I do I dont rev match and it still shifts smoothly. The rpms go slightly from 1,000 to 1,100 or so (maybe a bit higher). Do the rpms need to match perfectly or will a 100-200 RPM difference still be safe? Also, when I practice rev matching, do I hold the gas even as I shift into drive or do I let off? Thanks

I'm glad to have shed some light on the matter!

Being within 100-200 RPM is fine. If you can keep it within 100 that will be the smoothest transition -- anything more and you may begin to feel a slight jerk.

Hold the gas steady as you engage -- you want to hold that same RPM through the shift. You may need to add gas immediately after engaging due to the increased load you just added to the engine so that you can maintain speed, but you would want to do that anyway in a P&G situation.

So, just to be perfectly clear, pick a top speed. Shift into neutral and start gliding. Pick a lower speed. When you reach that speed rev match and hold the engine at that RPM level as you shift back to drive, then add gas to maintain or increase speed.

Got it. I have been practicing today on my commute to work and have felt no jerking. I am familiar with rev matching on manual transmissions but did not know this was possible on an automatic until now. Thanks for your wonderful advice!

You are very welcome! I hope that you find the technique as useful as I have. :)

Well another problem might be that if you are like me you can try and accelerate in neutral. I can tell you that the transmission frowns on this! :)

--des

I have a Jeep Liberty CRD Automatic and am not a big fan of turning off the engine at stop lights (wear and tear) but at a stop in neutral you burn less fuel than at a stop in drive. In Drive the fluid pressure is still building in your torque converter and uses more fuel than sitting in neutral. Example: My CFR (Calculated Fuel Rate) in neutral is ~6mm3 and in drive it is ~15mm3. So you use about 2.5X more fuel sitting in drive than in neutral.