TF-80SC at the lights
 

When in D do our auto boxes "disengage" after a period of not moving? And if they don't is it worth popping into N until you move again?

Best just to put the handbrake on...

I always go into N at lights

Why? In case I'm on a incline?

So I'm not asking because of that, I'm talking about a mechanism for prolonging the life of the box by disengaging when you haven't moved for a while, because you're stuck in traffic or at red lights. I believe some modern boxes have this but wasn't sure if ours had it.

Same here, but maybe we don't need to, maybe our box will disengage after a few seconds of having the brake on...?

you shouldn't sit at the lights with your foot on the brake blinding the people behind ,and the car is in a state of mobility if you get hit up the back so will go into the car in front too or into the pedestrian crossing in front of you. You should always apply the Parking brake when you come to a stop for an indeterminable amount of time. They make it so easy for you with an Electric Parking brake . It also contravenes the Highway code.

Highway code below...

In stationary queues of traffic, drivers should apply the parking
brake and, once the following traffic has stopped, take their foot off
the footbrake to deactivate the vehicle brake lights. This will
minimise glare to road users behind until the traffic moves again.
Law RVLR reg 27

No worries, from now on I'll use the parking brake.

.......and the parking brake handles hill starts and automatically releases as the car moves away. It's the first time I've had a parking brake like this and I always smile when I use it as it seamlessly lets me pull away. Unless I haven't put on my seat belt when Nanny Volvo wags her finger at me and won't let me drive away!

Parking brake aside, the original question is yet to be answered. Maybe we don't know?

I've been doing some testing and it's not entirely obvious if the box does or doesn't disengage after a few seconds of having the brake on.

To the best of my knowledge, the box does not disengage when sitting in D with the brakes on. I seem to recall (and may well be completely wrong!) that in some early versions it did do so.

I think the intention may have been to slightly improve the fuel economy but in practice it caused more problems than it solved and I believe the software was updated accordingly. Problems were said to include jerky operation and unpredictable behaviour when pulling away. I seem to remember it was the subject of much discussion on the forum at the time.

I have also seen it stated that taking the box out of gear for each stop causes more wear than simply leaving it in D with the brakes on. I can see the logic inasmuch as any clutch will wear during the engagement process and probably to a lesser extent during disengagement.

Minimising the number of times D is selected should help miminise the wear on the gear selection clutches.

My own practice is to hold the car on the handbrake and leave it in D unless the stop is sufficiently long to justify stopping the engine, for example at level crossings and some temporary traffic lights.

I've also seen it said that holding the car on the footbrake after heavy braking can result in the discs cooling unevenly and may increase the likelihood of them warping. However most modern handbrakes use the same discs and pads as the footbrake, albeit usually on just the rear wheels.

More hearsay than a definitive answer I'm afraid.

Martin