white_shark

Hey, I've done about 5k miles with the 17" run flat tyres and I can say they are alright. Not great though. Because for the first couple thousand miles I was wondering why the hell the steering at high speeds became so imprecise and wobbly. Like when doing long smooth bends on A roads, I had to basically "catch" the car as if it was constantly trying to steer out of the lane. Then I switched the steering from "comfort" to that other mode ("sport"?) and almost immediately felt a relief. It either got better, or I just learned to live with it. As for the ride, 17" run flats don't feel any better than 19" regular tyres on bumpy roads. I can't tell for sure since it's been a long time, but it's almost exactly the same. In the end, the only thing I gained with this replacement is the peace of mind. Perhaps it is worth it. Although, almost no one seems to be repairing even absolutely innocent punctures in run flat tyres in this country 🥶 If I were doing the replacement again, I'd probably go for 18" or even keep the original 19" wheels and buy runflats anyway.

Yeah, I know it may sound controversial but I am fine with increased stiffness as long as it provides me peace of mind when driving long distances. I've had two BMWs in the past with run-flats and they were perfect to me. No worries about potholes, punctures, even bulges are fairly safe and hard to make actually - just drive to the next service if something happens at 80 km/h. Whereas Audi's system of giving the driver a weak compressor and a tube of some crap to seal the punctures that ruins the tyre and ultimately leads to replacing a pair of them at least... well, this doesn't seem sensible at all to me. Probably, had I not have an uneven wear on the tyres, I would've kept the previous wheels and just bought a spare. But since I had to basically change at least a pair of tyres, or perhaps all of them, I went on to change the 19" to 17" alloys with Pirelli Cinturato P7 run-flat tyres in 225/50 size. After a few first kilometers, I feel no difference with the previous setup as expected. Given that 19" tyres are £50-60 more expensive each, it probably makes sense economically as well. At least if I manage to sell my old wheels 😅

Well, you may try to easily check the valve. Just knock on it with something moderately heavy when the car is warm but there's no heat. This is a very common issue when they get stuck due to purely mechanical reasons, so this either helps and you're getting hot air in a few seconds or not. If not, then perhaps it is the pump or something else, from lack of coolant to a leaking head gasket but hopefully it won't be anything serious. As to whether a diesel has it, I don't know.

If you trust them then it makes sense to replace the pump. Although I don't fully understand whether it affects anything at all when the engine is running at high revs. As I understand its purpose, it's supposed to help coolant circulate when the engine is idling or shut down. But I may be wrong. As to scanning, not sure about the pump but the valve is a simple on/off device without any sensors. So as long as the current is flowing through it (no matter is it stuck or not), the car will think it's ok. Perhaps the same applies to the pump but again, all this is a pure speculation and I don't know for sure. Good luck!

So the issue was resolved by the official Audi dealership under the "approved used" warranty for free. It was the coolant shut-off valve indeed, and they changed the coolant in the system as well.

Hey Al, it's under the bonnet on the passenger side near the washer blades. There's a compartment with a plastic lid, and the valve is there.

Thank you for response Gareth, Yes I don't expect to miraculously get rid of the 'sport' suspension effects and more to that, I am thinking about replacing my current tyres with run flats. Which should make the situation even worse, or at least cancel out the 19" to 18" swap 😄

Hi all, I am trying to figure out the best course of action for replacing my rims and tyres from 245/35 ZR19 93Y XL (currently fitted) to 245/40 R18 94H or even 225/50 R17 94H on an A4 avant s-line. The reasons to do that: The rear tyres are worn out badly, probably due to the lack of wheel alignment I really dislike the bumpy ride and too low profile The differential knocking when wheels are fully turned one way is really bad and is said to be worse on the lowest tyre profile So according to the wheel size calculator, 19" to 18" should be almost identical. 654mm overall wheel height for 19" vs 653mm for 18". But is there anything I am missing here? What alloys won't look terrible? I kinda dislike the current look anyways as the profile is too low and the car isn't sporty at all with its laughable 35 tfsi engine. But nonetheless, I'd prefer to keep it look nice. Thanks for recommendations in advance!

An update as I visited an indie shop nearby and an official Audi dealership. The local mechanics had discovered it was the coolant shut-off valve 4H0 121 671D. A simple solenoid, which intermittently gets stuck in a semi-closed or fully closed position. As I understood the schematics, this valve is preventing the (cold) coolant from circulating through the heater to make the engine warm up faster. According to multiple other forums' threads, it is very often stuck but many times in the open position, which of course goes unnoticed by owners. The worst is when an older revision part (B at the end) starts leaking and pushing coolant through the socket onto the wires, but this didn't happen in my case. All electrics is intact. Diagnostics (and temporary fix) are fairly simple: knock on it with something chunky such as a screwdriver handle a few times and observe the heat coming back. Importantly, it wouldn't show in the errors (unless the electrics is damaged and the circuit is always open/short) because there's no flow sensor and the device itself is passive. The only error related to the AC/heater I had was B108C07 related to the motor controlling the left air flap. And I am very glad I went to an indie shop first because I suspect the dealership, even if things were covered by the warranty, would do unnecessary replacements of the heater core, pump, thermostat, etc eventually damaging the system's integrity. To me, it was very confusing because it really reminded of a possible airlock, especially since there was a correlation between me adding coolant/revving up the engine and the heater getting back to life. Perhaps a stronger coolant flow would indeed push the valve into its place, who knows. The aux pump mentioned in the first message was suspicious too because of the outgoing hose being cold, but this was probably due to the closed valve, which also makes sense in retrospect. Anyways, the dealership are now requesting if the replacement is covered by the warranty and will fix it, including flushing and re-filling the entire cooling system. I am a bit skeptical about the latter but I guess it's ok as soon as they know what they're doing.

Tonight was about 5-6 degrees here in London and the heater worked just fine. Started blowing heat at about the second mark of the main coolant temperature display and kept doing so even after I stopped the engine for a while and then started it again. Now I am hoping that the diagnostics's gonna show something at least or it will remain a completely mystery. Perhaps some temperature sensor isn't working, which stops heater from working when it's cold outside. Or it was indeed an air lock in the cooling system.

Thank you Steve, will do. I am bringing the car to an indie shop tomorrow and to the Audi dealership on Monday so will keep you posted. Cheers!

Hi Ujwal, I have nothing to say about Audi's decisions but I personally chose 2.0 150 bhp over 1.4 150 bhp for a better reliability. At least in my perception, a 2L engine is sturdier than a 1.4 one but I am in no way an auto technician. Not sure I was right though as now I am fighting a barely working heater 🙂

Hello folks, I think I have reached the limit of my (mis)understanding of how the cooling system works in my A4 avant 35 TFSI and I'm gonna outline the symptoms I'm currently having. The car is a 19 reg bought about a month ago from the dealership with only 8k on the clock. When I start up the car, the engine warms up within 3-5 minutes of driving or idling and the temp indicator stays put at exactly 90 degrees. No fluctuation dependent on revs/speed/outside temperature, so overall it seems to be working fine. However, the heater might or might not work. In the morning, when the car is totally cold, heating usually starts working beginning at ~45 degrees of engine temperature and keeps doing so until I shut the engine or drive for too long. Starting up after a short break would most likely make heater blow only cold air. However, what helped me multiple times is revving up the car to 3000-4000 on the first gear on a slightly inclined road (facing the incline). Then within 10-20 seconds the heat would come back and stay until I either stop the engine or drive for long enough. This doesn't seem to visibly change the coolant level in the expansion tank though! Lastly, after revving up and 'fixing' the heater, there's a slight coolant smell in the cabin, which I won't mistake for anything else. Especially after accidentally blowing up the heater core ~15 years ago in a W201, which resulted in clouds of evaporated antifreeze going right into the cabin. I believe the issue is with the coolant flow as when the heating doesn't work, the incoming heater core hose (after the valve) is colder than the radiator upper hose. When the heating works, they are both about the same temp, or at least the heater matrix one is distinctly warm. All the dials and AC electronics seem to be working fine because when the heater works, it works perfectly. I haven't done any alterations to the cooling system or car whatsoever and I believe the previous owner or the dealer haven't too. They had barely serviced anything in the car at all as the mileage is low. The only thing I did was topping up the coolant by ~0.5L once as I saw the level dropping to the MIN mark on a cold engine when it became colder outside. Any help/suggestions/personal experience is highly appreciated! Thank you.

A few updates. The car stood for a while and then the cold temperatures kicked in. Heating stopped working altogether, no matter cold or hot engine. Coolant was at MIN level when the car was cold so I topped it up to MAX. Heating started working again while the engine is not fully warmed up. I thought that fault was with the G83 temp sensor (in the radiator's bottom hose), which apparently controls the aux water pump and the auto start-stop because both don't work. But it turns out, the bottom radiator hose is cold on the hot engine, which means it's the thermostat that's faulty. Quite disappointed that a 3 year old car with less than 10k on the clock already has such a trivial yet annoying fault. Will bring it to the dealership and try to fix this as well as do the full flush and cleaning of the cooling system. Hopefully it is covered under the approved audi warranty, otherwise will find an independent garage.

Hi all, maybe the issue I'm having will be useful to someone else as I've seen lots of threads about heating issues here but nothing mentioned the auxiliary pump faults. So the problem goes as follows. It's a A4 B9 avant 35 tfsi, 19 reg - bought it about 3 weeks ago from a dealership with less than 8k on the clock. I start the engine when the car is cold, everything heats up properly, coolant temp reaches 90 degrees and stays put no matter how fast I go/what revs, all good. Heater is working, fans, everything. Coolant level is between min and max. So basically no issues at all. But once I stop the engine and start it again (assuming there's some residual heat), no heat in the cabin anymore. Fans are spinning, temperature is fine, even the radiator fun is spinning but no heat. I touched the hoses everywhere to find the (possibly) faulty item and here it is, I suspect, an auxiliary water pump. The incoming hose is hot and the outgoing one, which goes to the cabin radiator, is cold. The item number is 06H-121-691-N. I am not exactly sure if it is the only faulty item, if the failure is hardware or software, or whether it's the root cause. Has anyone had/heard of something similar? Any advice is highly appreciated since I am now waiting for the reply from the dealership and how they suggest to deal with it.

Hi Karol3dd, Not sure you've already made your decision or not - but I just purchased a 2019 a4 b9 with 19" wheels (fitted originally since it's an S-Line) and I am thinking about replacing them to 18". IMO the ride is kinda too rough and I also am not a big fan of such low profile. It's 245/35, which is in my opinion way too low. Cheers,