Norman99

Greetings everyone. My wife and I drive a 2015 Q5 TDI and really like it. It has about 114,000 miles at the moment. Two questions.

First, I asked the service tech at our local Audi dealer when the rear differential oil should be changed. They basically said never and that once you open the rear diff up to even check the oil, the oil goes bad for some reason. Furthermore they claimed the rear differential is designed to be sealed for the lifetime of the car. This does not sound right, particularly since a diesel will typically last longer than a gas engine. Can anyone point me in the right direction here?

Second, I also asked when they recommend that the injectors be cleaned as it is typically at 80k on a gas car. They said they never clean them, they just replace them when they stop working. Perhaps the fuel filter for the diesel is better, I know CAT diesel filters are 3 micron where as gas fuel filters are typically 30 microns or larger. But still, I would like to ask here as it seems like cleaning the injectors would prolong the life and give you better fuel mileage.

Thank you for your help.

John

silver_tt

Hi John. I have a 2.0T but here's my input as it should apply to your car:

The diffs on these cars can be serviced. If you open it up you might as well change the fluid. There is no such thing as lifetime fluid. Audi is misleading in this regard as "lifetime" really just means until you are out of warranty and they don't need to worry about it anymore. My Audi dealer for example would have told you differently knowing that you want to keep the car out of warranty.

I would never, ever clean injectors on any car. If you suspect you have a bad injector -- leaking, not spraying properly, whatever, just replace it. Fortunately my 2.0T has a cast iron block and your TDI I would guess does too. But especially if you have an aluminum engine with cylinder liners like Alusil you should be extremely careful as a leaking injector can literally take out your engine. On cast iron it wouldn't necessarily be so great either though and could destroy your rings. In short: When in doubt on injectors..........replace do not clean!

S4'ed

Your Service Tech is full-of-sh_t.....

Timber91

Silver_tt, you do realize the OP is asking about Diesel injectors for their TDI? Octane boosters are worthless and may, potentially, be harmful. Running quality diesel with no water is critical to the fuel pump as well as injector life. High volume diesel dealers such as truck stops are helpful. If you can also get higher cetane diesel, you'll reap the rewards of increased power and mileage.

Norman_99, I also have a '15 Q5 TDI and have done the rear and front diff twice, as well as the trans and "transfer case". Currently stand at 144,000 miles and runs like new. As mentioned, though, lifetime for Audi is not necessarily lifetime of car in your eyes. ZF, the trans manufacturer, recommends 75,000 +/- for fluid and filter. Diffs can't be, realistically, all that different. My work trucks suggest every 50K for diffs. When you throw on how easy they are to do DIY on these cars, it's a no brainer for peace of mind.

Take a minute to search here for TDI info. Mythdoc, MurrayA4, and others have been invaluable with information and experience.

silver_tt

Correct. I was talking about the 2.0T and the additive is for gasoline only....the perils of responding from a phone.

edit: deleted as to not cause confusion

nordicb

At 120k miles I changed diff oil. It was very clean, even the distinct strong smell remained, as expected really, but I did it just as an inspection, level, internal damage, etc. I change all fluids in the car, regardless of what others say.
As for cleaning injectors, I think would first be looking if there are any signs that may indicate injectors problem, otherwise I would leave them alone perhaps. You can check how cylinders perform via diagnostics, leaky or bad injectors will most likely cause ECU to compensate for them more than others.
Front diff, gearbox, PAS, brakes will also benefit from oil changes.

silver_tt

Good observation. I would just point out that ATF is a very complex fluid. It can look clean, have the same smell as new, and basically seem the same as it was new when you drain it.... but it's not. Over time any fluid will start to break down and lose its properties that are protecting your transmission internals. So changing the fluid every 75K or whenever the manufacturer suggests is cheap insurance. We have a friend who had a diff go out in the last year or so and it was quite expensive I am told.........

Norman99

Thank you everyone! I have learned quite a bit from your posts and really appreciate the suggestions and advice. I will get the fluids changed in the rear diff, front diff, and transfer case at the next oil change, which will be at about 120,000 miles. I did have the transmission fluid changed at about 75,000, so I will do that again in due course. And yes, using a high quality injector cleaner makes a lot more sense since the dealer is not set up to clean them. Best to you all, John