Tyre Pressures Dropping

[hshah]

I've had my new A6 BiTDI since July and just crossed 5k miles. About 6 weeks ago a message popped up stating that rear right was low. When I topped them all up, every other one was down by 3 psi (from the specified pressure) but the rear right was down by 9.

Today a message popped up stating that the rear left was low and the front two were down by 3 but the rear left was down by 11 and rear right down by 8.

What is going on? My mpg for local driving hovers around 32 and motorway gets up to about 43 so I have noticed an issue with that. In one of the other threads on here I had mentioned that I can feel a lot of heat coming from the rear wheel areas, and that could be after only a 9 mile journey. I haven't got round to taking my car into Audi but curious to find out what could be causing this sort of behaviour.

[niall campbell]

You need to get better tyre sealant on the wheels itself.

I ask for " the black gooey sealant " and explain the alloys have slow punctures round the rims

You will need to ask for this at every tyre change.

As for the hot rear wheels, this could be the electronic parking brake beginning to seize, however I am more inclined to think that they all suffer from slight brake bind due to the EPB.

[hshah]

You need to get better tyre sealant on the wheels itself.

I ask for " the black gooey sealant " and explain the alloys have slow punctures round the rims

You will need to ask for this at every tyre change.

As for the hot rear wheels, this could be the electronic parking brake beginning to seize, however I am more inclined to think that they all suffer from slight brake bind due to the EPB.

Well the car was brand new so surely this is something Audi should have covered? Plus the front wheels aren't dropping so much... it is just the rears.

[zollaf]

tyre pressure will vary with heat. a drop in temperature or a run on the motorway will see a variation of a few psi, but it does seem you may have a problem, possibly a puncture. i doubt it will be a sealing problem on a brand new car. probably best to get it checked by covering it in water and looking for bubbles. tyres should be checked weekly to ensure correct pressures and to ensure the safe handling of the car. a dash display isn't always accurate, as you have found out.

[ukgroucho]

My allroad BiTdi was an early July collection 2 years ago when the temps were in the 30C range. Late in September or early Oct that year I headed off one morning when temps were much lower (in the 12C range if I recall) and has a "check tyre pressures" warning - for all 4. Sure enough they were all down by some amount (cannot remember) and I put it down to the change in ambient temps causing a drop in pressure. However, once rectified the problem did not reappear.

The fronts being down another 3 psi after 6 weeks could be temp changes again but the rears dropping as much as they have would be a worry. However one thing does concern me - the heat that you mention from the rear wheels. That's not right. One issue with that is that you may have re-inflated your rears when they were warm - so you thought you'd stuck 33psi or whatever in but when they cool they are down to 28psi. It takes a little while for the automatic pressure sensor to "see" a pressure change issue so if they are warming up rapidly when you drive it could mask that discrepancy.

A couple of things I would suggest.
- Leave the car sitting so all tyres are cold and re-inflate to correct pressures. Ideally you want to do this on your driveway at home after the car has sat overnight and use a separate digital pressure gauge - don't rely on the crap that is built into foot pumps usually. If you need to take it to a garage cos you don't have a foot pump etc. then make it a short trip and check the tyre temps so you understand if it's causing a discrepancy.
- You need to get to the bottom of the heat you are sensing from the rear tyres. Assuming it's happening even with moderate driving - and based on the assumption that you do a lot of start stop driving because you are in London - I'd suggest switching off the driver aids that automatically apply the brakes. So always manually disengage the handbrake by pressing the button before pulling away and turn off the hills assist auto brake thing. You really don't need it in an auto anyway and there have been accusation (Honest John etc.) that those systems cause excessive rear pad wear - which would also generate heat.

Beyond that take it back to the dealer and ask them to investigate.

[hshah]

My allroad BiTdi was an early July collection 2 years ago when the temps were in the 30C range. Late in September or early Oct that year I headed off one morning when temps were much lower (in the 12C range if I recall) and has a "check tyre pressures" warning - for all 4. Sure enough they were all down by some amount (cannot remember) and I put it down to the change in ambient temps causing a drop in pressure. However, once rectified the problem did not reappear.

The fronts being down another 3 psi after 6 weeks could be temp changes again but the rears dropping as much as they have would be a worry. However one thing does concern me - the heat that you mention from the rear wheels. That's not right. One issue with that is that you may have re-inflated your rears when they were warm - so you thought you'd stuck 33psi or whatever in but when they cool they are down to 28psi. It takes a little while for the automatic pressure sensor to "see" a pressure change issue so if they are warming up rapidly when you drive it could mask that discrepancy.

A couple of things I would suggest.
- Leave the car sitting so all tyres are cold and re-inflate to correct pressures. Ideally you want to do this on your driveway at home after the car has sat overnight and use a separate digital pressure gauge - don't rely on the crap that is built into foot pumps usually. If you need to take it to a garage cos you don't have a foot pump etc. then make it a short trip and check the tyre temps so you understand if it's causing a discrepancy.
- You need to get to the bottom of the heat you are sensing from the rear tyres. Assuming it's happening even with moderate driving - and based on the assumption that you do a lot of start stop driving because you are in London - I'd suggest switching off the driver aids that automatically apply the brakes. So always manually disengage the handbrake by pressing the button before pulling away and turn off the hills assist auto brake thing. You really don't need it in an auto anyway and there have been accusation (Honest John etc.) that those systems cause excessive rear pad wear - which would also generate heat.

Beyond that take it back to the dealer and ask them to investigate.

When I reinflated them today I had driven 0.4 miles to the garage after letting the car sit for about 7 hours... they were pretty cold at the time so I know what I have put in is pretty accurate. When I had topped them all up 6 weeks ago I had driven about 2 miles and again that was after leaving the car parked for about 5 hours.

I don't use the hill hold and I rarely let the car stop when I'm at lights etc. When I mentioned the heat in the other thread someone did mention brakes sticking, and it would also explain the low mpg.

[morski]

Nex time you feel the heat from the rear touch the alloys and check if they feel hot; if so then the brakes are definitely binding.

[Splash]

I experienced some heat build-up in the front and experimented by letting the car coast up a little-used motorway slip road (M6 Shap Southbound) where I parked offroad within a few metres. Despite almost negligible use of the brakes there was slight warmth in N/S F wheel. Mentioned this to the dealer but they said all checked out OK. I'll mention it again at the next service.

I can understand the efficiency systems and engine heat creating some warmth at the front (although not at motorway speeds), but not at the rear.

I lent my Michelin digital pump to a guy who was stranded at a remote beauty spot with 2 punctures the other day, so he could at least crawl back to civilisation. Not heard back from him so I picked up one of the cheap digital pumps ALDI currently have for £17. It might encourage my wife to check pressures in the other car too. Still hoping the unknown motorist will get in contact to return my pump or at least leave it where I suggested, restoring my faith in humanity.

It was a bit of a gamble anyway as another car also had a spare on and my spare wasn't a matching size if I too got a puncture.

[Whippy53]

That was nice of you, I hope you get it back!

[MarkTM]

In the absence of an alloy wheel protectors fitted (these are notorious for allowing air out) I would suspect either a poor seal on your rims or else faulty valves.

[hshah]

In the absence of an alloy wheel protector fitted (these are notorious for allowing air out) I would suspect either a poor seal on your rims or else faulty valves.

Odd that it is both rears and the fronts are fine.

[Bar Shaker]

You should always set your tyre pressures with the tyres up to operating temperature, from the sort of driving you typically do. Between summer and winter a cold tyre can easily vary 3-4psi. A cold to warm operating tyre can vary twice as much as that.

If you inflate your tyres to XXpsi when cold, once warm the grip will be reduced and the centre section will wear much faster than the outsides as the tyre will be over inflated.

Warm the tyres up, set the pressures accurately and then leave the car over night. The following morning, re-set the pressure monitor. If the pressures ever fall below this new 'cold' pressure setting, you have a puncture/seal failure.

[Sam]

Warm the tyres up, set the pressures accurately and then leave the car over night. The following morning, re-set the pressure monitor. If the pressures ever fall below this new 'cold' pressure setting, you have a puncture/seal failure.

Michelin advise you to check pressures when cold but also state that if the tyre is warm you should increase the pressure by 4 to 5 PSI over the manufacturer's recommended pressure (see here (http://www.michelin.co.uk/tyres/learn-share/care-guide/guide-for-tyre-pressure)). Most, if not all tyre manufacturers agree.

I'm hoping they're not all in on an elaborate ploy to make us wear our tyres out sooner.

[MarkTM]

Odd that it is both rears and the fronts are fine.

Maybe because they're the ones with the leaks? :)

[Splash]

That was nice of you, I hope you get it back!
Thanks Whippy.

He probably keyed in my mobile number wrong (no signal to test as it was in the hills), but I optimistically phoned the backup drop point (local ice cream maker/adventure playground) and sure enough he'd dropped it off.

Felt so pleased, I bought my own ice cream... ;)