Air Suspension Observation.

[IvanR]

The air suspension on the D3 is working fine and even when left in the garage for a week or more at a time at home there is no lowering of the suspension that noticeable to the eye.
However what I have noticed is when on outback trips, with the D3 fully loaded, EG on the Simpson crossing, in the morning the vehicle would have lowered to the extent that it was noticeable.
On startup the compressor fires up, D3 raises and every things fine for the day. It is only occurs when the tracks are rough and the going slow.
Just wondering if anyone else has had similar experience.
One "theory" I have is with the going being so slow that the air in the air bags heat up and expand (especeally the front with engine heat) then with the cold night temperatures (close to zero) the air contracts and the car sinks. Just an observation.

IvanR

[bbyer]

My guess is that at home, your 3 is parked on relatively flat level ground whereas outback, it is not.

I do not actually understand how the nocturnal auto level system decides the 3 is level, but I gather it is not the yaw sensor but instead some reading the individual wheel height sensors.

I gather that if the 3 decides it is not level, some air is released from one or more corners in an attempt to bring things into level according to the wheel sensor readings. If then, each time the system again wakes up and decides for whatever reason, the 3 is still not level, more air is released. I expect that if one or more wheels are significantly more or less extended than the others, the system logic will just keep trying to even out the readings.

If my above explanation is correct, I find it difficult to believe that Land Rover did not provide for rough ground in their thinking. It seems however that when parked on a plane surface of a steep hill, no air is released as all sensors would be reading about the same degree of air spring extension or compression.

At the same time, this may be why LR has that high centre extended height feature. If one parked the 3 on a typical rock climb surface, and departed for an extended lunch, your 3 could be high centred when you returned.

[BobD]

BByer, you may be right about the constant re levelling. I did a trial hook up of my caravan while I tried out the new adaptor I made up between the LR plugs and my Geist's 12 pin plug and left the engine running for 15 minutes or so. The whole time it was running it was lifting up one rear corner slightly then letting it down again. I was wondering what the hissing was and then noticed it going up and down a few millimetres. Because of the slope of the drive and angle it was on to hook up to the caravan the car was slightly uneven so it must have prompted the computer to try to level it.

[isuzurover]

One "theory" I have is with the going being so slow that the air in the air bags heat up and expand (especeally the front with engine heat) then with the cold night temperatures (close to zero) the air contracts and the car sinks. Just an observation.

IvanR

I believe you are right. I have noticed the same when the weather changes significantly.

EDIT:

PV=nRT. So if pressure is kept constant, hotter air will contain fewer molecules for the same ride height, which also means less air in the air tank to relevel the suspension or maintain ride height as things cool down.

[Graeme]

I expect that if one or more wheels are significantly more or less extended than the others, the system logic will just keep trying to even out the readings.

The WSM mentions average height for an axle for front vs rear height and I suspect diagonal variations from average heights are used to determine low corners.

[Stuart02]

The WSM mentions average height for an axle for front vs rear height and I suspect diagonal variations from average heights are used to determine low corners.

Maybe that's why my D4's front left is dropping overnight at home... It's bad at maths?

[Graeme]

.. which also means less air in the air tank to relevel the suspension or maintain ride height as things cool down.

Bear in mind that the suspension does not attempt to maintain height during relevelling, only releasing air from springs to a point after which no more levelling occurs.

[IvanR]

Yes Graeme I had not thought of self levelling, but changes in air pressure may be part of it. On my D1 which has poly airs, a 5psi increase in pressure see's it lift quit a bit. I quess this is just one of example of these machines having a mind of their own.

Ivan