Air suspension settling?

[ianoliver57]

X358 with 33000 on the clock. 2009 model. Is it normal for the suspension to sink when the car has been parked up for a couple of days, or, is there a problem developing! Noticed this morning the gap from the top of the tyre to the wheel arch on front was two fingers (highly technical measurements) but after a short run, the gap was a full three fingers!
Any thoughts?

Regards

Ian.

[BrianG]

The X350 will self-level over a 24 hour period when parked, most noticeably if your driveway (like mine) is not flat. As long as it doesn't get any lower than "two fingers" then it probably doesn't have any problem with leaks. The official measurements (from wheel centre to wheel arch) are front: 386mm +/- 15mm and rear:373mm +/-15mm.

If you don't get any warning messages when you start up then I would expect the air pump to be satisfactory. (I recently had to get a new pump fitted at 133,000 miles to stop random amber warning light and "air suspension fault" messages in the speedo display strip, the sign of a failing pump.)

[ianoliver57]

Thanks Brian, puts my mind at ease. I will keep an eye on it.

Regards

Ian.

[PaulGover]

The suspension height can also change with (external) air pressure and temperature - i.e. weather, as well as changing loads.

After a trip, it enters "post" mode, where it will raise the car to compensate for the air in the system cooling. After 90 minutes switched off it enters "sleep" mode, and the suspension only adjusts once every 24 hours, and then only downwards, to get all 4 corners about the same height. When you open a door or the boot, it enters "preliminary" mode, where it will start correcting discrepancies in the height relatively quickly (to make up for loading and unloading), though with a larger latitude that usual.
With the engine running but the car stationary, it enters "stance" mode, where it will correct rapidly and with a small latitude to discrepancies (either from earlier settling, or changes in load, such as people entering the car).
Once on the move, it will further correct, with a smaller latitude, though slowly to react so as not to be confused by road changes (it's not an "active" air suspension) typically when you first stop moving at say traffic lights or a roundabout. There are several other modes (jacking, towing, cornering), including "overloaded", where the car will drop 15mm quickly if the air pressure needed to restore normal height is too high - in which case ask the heaviest passenger to get out .

The tolerances are:
Preliminary: +15 to -30 mm.
Stance and Drive: +/- 9mm.
Post: +/- 6mm.
Normally the compressor only runs if the engine is turning at more than 400 rpm and the road speed is over 25 mph, but if the suspension is too low (-40 mm) it will kick in whatever if the ignition is on - that's typically the result of a leak such as a torn air bag.

(all that taken from the dealer training document that's floating about somewhere on the Internet).

All that said, if it's constantly drooping, you may have a leak. Good leaks are loose connections or damaged hoses, as they're relatively easy and cheap to fix. Bad leaks are splits in the suspension air bags, 'cos they will probably get worse in time, and you're looking at around £900 for a new strut if you do it yourself, rather a lot more if you go to a dealer.

[ianoliver57]

Thanks Paul. I can now monitor it properly although it does seem to drop more on the front rather quickly ie less than 10 hours parked. Problem I have is the Jag specialist is 2.5 hours drive away.

Regards

Ian.

[ptjs1]

Great detail from Paul on the operation of the system!

Ian,

If it's dropping overnight or over just 2 days AND you're parked on the flat, then you might be looking at a leak on one corner, or else a dodgy height sensor. The way that the car will self-level downwards with the ignition off means that if you've got a problem with a leak or sensor on just one corner, it will take all the corners down to self-level. And then do it again if the same corner has dropped again / given a false reading.

Good luck with the diagnosis.

Paul

[ianoliver57]

I still need reassurances that there is not a problem. I’m in Glasgow on the 5th and the good guys at Prestige Jaguar in Paisley have managed to ‘squeeze’ me in in the afternoon to check over the suspension.
Last week, completed a 400 mile round trip to Dumfries to visit family. Car performed beautifully all the way. Overall milage for the run came in at 30.7 mpg. Really impressed with that.

Regards

Ian.

[ianoliver57]

Update on sinking suspension. The car was in with Prestige Jaguar in Paisley last Friday. Full check carried out with all the air struts /bags examined. They detected a leak in the o/s/f bag, which although small, would be enough to cause the side to sink. New strut required. When they checked the cost of a Jaguar replacement we were both shocked at the figure. Over £1400. Just for the strut! Crazy. Prestige suggested fitting good quality after market but said both sides should be done. Even with that, it is still £600 cheaper than one Jag strut! Parts have been ordered. Just waiting for Prestige to find a suitable window in their busy schedule to fit.

[ptjs1]

Ian,

I guess you've shopped around? You can get cheap aftermarket ones with 2 year warranty for c£200 each, or a Bilstein one for c£600.

Good luck

Paul

[ianoliver57]

Thanks Paul. With suspension struts, I think quality is more of an issue than price (but not Jaguars price!) I’ve even seen them on e bay at £140! The struts that Prestige recommended are £440 with a three year warranty. I’m happy with that and to be guided by Prestige whom I’ve dealt with for years now. So having shopped around, I’m happy to go with struts at £440 and 3 year warranty.

Regards

Ian.

[PaulGover]

AFAIK the cheap struts are Chinese copies that do not have the electronically controlled damper; instead they have a dummy plug wired to fool the ECU involved. The Bilstein originals, with the electronic gubbins, are about £900 from the usual suppliers. I didn't find any alternatives with the fancy dampers when I looked last year.

[ianoliver57]

Think I found what I need at www.aerosus.co.uk . Select X358 model from 2009. Seems to have all the ‘gubbins’ needed.

Hope I’m right!

Regards

Ian.