Stage 2 3.0t vs stock 4.0t reliability

[S4Sumi]

I’m looking into purchasing a c7 but can’t make up my mind on which one...looking at an a6, s6, a7 or s8. I know these are all different cars but...if I were to go with the 3.0t I would go stage 2. Just curious about reliability and what problems to expect between a stage 2 3.0t and stock 4.0. Any opinions or experience please...

[dc2002]

There are many many stage 2 3.0T's out there including the S4 platform and i have not heard yet of anything catastrophic - blown engine, supercharger, transmission....etc.

The 3.0T is astonishingly reliable.

I get 30+ MPG on longer highway trips.

The biggest downside is probably not having the DSG transmission like the 4.0T has.

Plus there are so many 3.0T's out there that even finding a used motor or trans should prove to be reasonable VS the 4.0T.

Just my $0.02...go with the nicest A6 you can find and go right to stage 2.

[OaborbaG]

There were a lot more 3.0T engines made than 4.0T, and they are in a lot more vehicles. Just look at all of the blown turbo threads compared to 3.0T issues. While the 4.0T turbo issue has probably been blown out of proportion, because there are a lot of stage 2 4.0T cars with many miles on them with no issues, the 3.0T can be fixed a lot cheaper, mainly because of how many more are available. Plus, they can be made just as fast, look at p3u's car.

Drive ability would be different since it has the ZF 8 speed instead of the DSG, but that could also be a good thing depending on who you ask.

I think the biggest question to ask yourself would be do you want the air ride and the diamond stitched seats of the 4.0t.

[Audibot]

The biggest issue with the 4.0T is that the oil screens for the turbos can get clogged up over time, leading to oil starvation and eventual turbo replacement. Now, this is covered under warranty if you are still under warranty, but if not, you're better off slapping upgraded (RS7 or otherwise) turbos and getting tuned. Idk how much it costs for Stage 2 on a 3.0T, but even a Stage 1 tune on a 4.0T will push you at or over 500 hp, with no noted ill effects.

Regarding the 8HP ZF transmission (non-DSG), it's still a great transmission. I have it in my TDI (which I wholly love and can certainly recommend unless you absolutely need/want hp). Much better than the previous ZF 6HP models. Much more responsive to inputs (never hesitates to get out of 8th gear, for instance) and paddle inputs are very quick as well. Naturally not as quick as a DSG, but having driven a few loaners with the DSG (all 4-bangers, name you), I didn't care for it as much. I'm sure it's a different story with more power to push through the rev range.

Btw, whichever 3.0T or 4.0T you get, you can enable "Efficiency" mode in Drive Select and choose that if you are on a long cruise and want the mpgs--it limits throttle response but folks are claiming near 30 mpg in a 4.0T whereas previously they'd get mid-20s tops.

[pfar54]

The biggest issue with the 4.0T is that the oil screens for the turbos can get clogged up over time, leading to oil starvation and eventual turbo replacement. Now, this is covered under warranty if you are still under warranty, but if not, you're better off slapping upgraded (RS7 or otherwise) turbos and getting tuned. Idk how much it costs for Stage 2 on a 3.0T, but even a Stage 1 tune on a 4.0T will push you at or over 500 hp, with no noted ill effects.

Regarding the 8HP ZF transmission (non-DSG), it's still a great transmission. I have it in my TDI (which I wholly love and can certainly recommend unless you absolutely need/want hp). Much better than the previous ZF 6HP models. Much more responsive to inputs (never hesitates to get out of 8th gear, for instance) and paddle inputs are very quick as well. Naturally not as quick as a DSG, but having driven a few loaners with the DSG (all 4-bangers, name you), I didn't care for it as much. I'm sure it's a different story with more power to push through the rev range.

Btw, whichever 3.0T or 4.0T you get, you can enable "Efficiency" mode in Drive Select and choose that if you are on a long cruise and want the mpgs--it limits throttle response but folks are claiming near 30 mpg in a 4.0T whereas previously they'd get mid-20s tops.

How do you enable efficiency mode? I only have dynamic, comfort and custom as options.

[Audibot]

How do you enable efficiency mode? I only have dynamic, comfort and custom as options.

https://www.audizine.com/forum/showthread.php/857957-Activating-Efficiency-Mode-VIA-VCDS-ALL-THE-MPG

Doesn't seem to do anything on my TDI but should help other C7 vehicles

[SPONGE]

https://www.audizine.com/forum/showthread.php/857957-Activating-Efficiency-Mode-VIA-VCDS-ALL-THE-MPG

Doesn't seem to do anything on my TDI but should help other C7 vehiclesI just traded in my modified dual pulley A6 with tcu tune. I have no regrets and 1 year warranty left on the S6. I will mod once the warranty expires. But its a totally different car. From the driving experience to the feaures.

[SPONGE]

Gas mileage is terrible on the 4.0T in comparison to my modded A6 tho.

3.0T was very reliable no issues outside of standard maintenance

[pfar54]

https://www.audizine.com/forum/showthread.php/857957-Activating-Efficiency-Mode-VIA-VCDS-ALL-THE-MPG

Doesn't seem to do anything on my TDI but should help other C7 vehicles

Thanks! What is the best VCDS tool I could buy to support doing this?

[Audibot]

Thanks! What is the best VCDS tool I could buy to support doing this?

VCDS

/thread


I'm not sure if OBD11 or Carista could do it. Probably the former at least. I have a full-fledged VCDS (unlimited) I bought back when I got my B7, and it's been one of the best purchases I have made.

[bknewtype]

cross shopped a newer a7 3.0 vs a pre fl 4.0.

imo nothing can replace the feeling of a 4.0 v8 TT. feelings intoxicating. not to mention the v8 noise it makes. id b happy to pay the price in maintaining a less relaible car if it meant mores miles when it works.

jhm released the oil relocation kit so, for a few grand in parts and labor you can completely eliminate the " known" turbo issues on these cars, and toss a few more grand and you can have yourself some rs7 turbos with 0 issues ( assuming you do both the jhm kit + turbo upgrade ). imo a great deal to beef up your car while maintaining reliability in 1 shot

[wwhan]

Gas mileage is terrible on the 4.0T in comparison to my modded A6 tho.

3.0T was very reliable no issues outside of standard maintenance

My old stage 2 B8 S4 had the dreaded thermostat failure, hopefully the newer 3.0T (newer than 2014) are more robust. There were some issues with the 3.0T harmonic balancer crank pulley failing.

The main issue on the 4.0T is the clogged turbo oil supply screen causing early turbo failure (JHM bypass screen (https://jhmotorsports.com/stainless-braided-turbo-oil-line-and-strainer-screen-relocation-kit-jhm-serviceable-for-tsb-2044640-on-c7-d4-4-0t.html)may a solution).

Other 4.0T issues are;
See the cam adjusters notes outlined in the ATU, ATU for Cam adjuster (https://static.nhtsa.gov/odi/tsbs/2018/MC-10150761-9999.pdf)
Oil dilution by the fuel can cause hard starting - which might be related to the seal on the HPFP & driving very short distances (TSB has software update, 2046724/7).
The 2013 models had leakage of turbo coolant lines.
The PCV Oil seperator may fail at 50k miles.
There may be issues with the manifold flaps.
Some of the early 4.0T had thermostat issues & there is a TSB on that.
There are TSBs on all of these. See TSBs; 2044640/5, 2040644/3, 2046724/7, 2041097, 2041097, 2041097, 2048411/3

The 3.0T gas mileage varied, depending on how I drove it, but no worse MPG than the stage 1 S6.

There were times when the 3.0T gas mileage dropped to 8.9 mpg, being aggressive on the throttle, but typical in town was 13 mpg, best in town was 16mpg. On a flat freeway, 72 mph and cruise control, it would reach 28mpg.

On the S6, in town gas mileage is around 13 mpg, but sometimes 11 mpg, best in town around 16mpg. On a flat freeway, 72mph and cruise control, it would reach 28 mpg.

The newer model years should have less problems on the 3.0T & 4.0T.

If you look up the TSBs on the year models you are considering you can see most of the possible issues, by looking here https://www.nhtsa.gov/recalls under Manufactures Communications, the engines section

[wwhan]

Thanks! What is the best VCDS tool I could buy to support doing this?

https://store.ross-tech.com/shop/vchv2_ent/

[agent47]

It was game over for me when I test drove the 4.0TT. The engine growl in itself was one of the reasons. Add to it the subtle interior upgrades, the sport differential and the exclusivity.
Yeah you can make the 3.0T as fast, but how often are you going to take it to the track or street race other sub-11s cars to prove you are quicker? At the end you will have spent a good amount of cash on the mods. Even in stock form the 4.0TT is plenty quick. I have done a few friendly pulls with some cars and my S6 didn't cease to amaze. Yeah the fuel economy sucks a donkey's dick on the S6 but pedal to the metal justifies it for me [emoji1787]
I bought mine CPO based off of the turbo failure reports. 5k mi oil changes and the turbos are still looking good. A few people have actually cut out the oil screens completely and have had no issues. If your wallet agrees, then go for the 4.0TT.


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[digdah]

The 4.0TT can be surprisingly efficient if you do lots of highway miles and/or you drive like a grandma

[bknewtype]

The 4.0TT can be surprisingly efficient if you do lots of highway miles and/or you drive like a grandma

This 100%. Im used to driving all my cars in manual mode only so when i first got the s7 it was no different. Averaged around 10-14 mpg even on highways. My buddy said the v8 4.0 is actually pretty fuel efficient do i decided to put it in D for some of my highway drives and i get around 24mpg with mostly cruising and some hard accelerations. Ill take it

https://uploads.tapatalk-cdn.com/20190717/19b8d919eeb21b4b413baa6ffd08cf6c.jpg


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[teknikk7]

While the 4.0 has known issues, many have zero issues. I just picked up a S6 and have zero regrets. It’s such a beast, and the sound is amazing. Oh that diamond stitching and flat bottom wheel....so sexy. And I just lowered it via VagCom, it looks so pretty. Add in the front blacked out grill and side mirrors from eBay, both for under $400. She’s a looker.

[Hofahome]

3.0t is likely more reliable than the 4.0t. The 3.0t is really a great little motor and I miss the immediate power delivery. BUT, I would not switch back to my S4. The 4.0T is a brute of a motor.


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[zx9eric]

While the 4.0 has known issues, many have zero issues. I just picked up a S6 and have zero regrets. It’s such a beast, and the sound is amazing. Oh that diamond stitching and flat bottom wheel....so sexy. And I just lowered it via VagCom, it looks so pretty. Add in the front blacked out grill and side mirrors from eBay, both for under $400. She’s a looker.

I, Like you, have 0 regrets purchasing a 4.0t even after having the "catastrophic turbo failure". I assumed the turbo failures were a bit blown (no pun intended) out of per-portion. But, it did happen to me as well. This is an amazing car with great comfort, performance and looks. If I were you, I would still have the check valve and oil screen replaced and the oil separator while you are there. Enjoy the car,!