Audi Q7

[Sully]

We have towed out Elite II now for about 30k with our Audi Q7, so I wanted to give an update.  98% of the time the Audi does a nice job, the issue I have had is on long steep, curvy down grades.  Coming into Death Valley from the west there is a 6% 15 mile downhill, using 3rd gear and only applying the breaks for short intervals, I still over heated the car breaks to the point that we were seeing smoke.  The breaks never faded but it was a very concerning situation.  We have crossed the Rockies multiple times without incident but the steep down grades were limited to a max of 6 or 7 miles.  The long 15 mile downgrade with lots of turns required keeping the speed under control using a lot of braking.

[rich.dev]

Dave, nice hearing from you and glad your Q7 is performing well. Sounds like you and Kris are really putting on the miles! I retired end of September 😊 and Thea and I are now full timers, left Guelph end October to escape the Canadian winter enr to Arizona, currently in Texas and should be in the Quartzsite area in a week or so. I traded my Touareg TDI in on a Silverado 2500HD, loved my Touareg, it towed like a champ, but with us going full time it lacked cargo capacity. So far liking the Chevy but also missing the Touareg’s fuel efficiency and turning radius. Take care and happy camping, say hi to Kris. 

[jd1923]

1 hour ago, Sully said:

I still over heated the car breaks to the point that we were seeing smoke.  The breaks never faded but it was a very concerning situation.

Over-heating is cause for brake fade. Given you actually saw smoke, you likely had some brake fade, or cheap pads which would not be OEM on an Audi. Wow not safe, pull onto the shoulder and park 20-30 minutes (longer if hot outside) to lower temps.

Another thing. If brake fluid is anything but clear liquid in a vehicle over 3-years-old, dark yellow or worse brown in color it should be replaced, pump and bleed until new clear fluid is showing at the bleed screw. Yellowing fluid shows there is moisture in the fluid.

Dot 4 brake fluid when dry (new) has a boiling point of 440F. When wet 310F and in worse condition gets even lower, as the boiling point of water is 212F. The water in brake fluids will turn to steam when these temps are exceeded creating brake fade or worse brake failure. It is standard maintenance in street motorcycles to replace brake fluid annually. I do it every 2-3 years living in the SW and only riding occasionally around town. I replace brake fluid in cars & trucks every 5 years and if I lived on the coast or anywhere east, or anywhere cold, I would replace the fluid every 3 years, especially in a tow vehicle.

You likely also need to increase the gain on your trailer controller. See this post:

 

[Sully]

Hi Rich, congratulations on retiring.  We stopped in Vegas to get an Audi tech opinion on what was going on.  We saw the smoke when I pressed the accelerator after the long downhill.  Audi shuts off fuel and ignition when you take your foot off the accelerator.  He believes that our rings are a little worn and with the engine at 4 to 5k rpm downhill for an extended time that some oil is building up in the cylinders, then pressing the accelerator ignites the oil causing the smoke. We are heading up to Cheyenne to visit family then will be heading for Texas.  From there we are going to Florida and then back thru Arizona on the way home.  Kris says hi to both of you.  We will touch base when we get to Arizona to see if you are still around.

[rich.dev]

3 hours ago, Sully said:

We will touch base when we get to Arizona to see if you are still around

Sounds good, we will be in the Quartzsite/Yuma/Lake Havasu area until end Feb, then down to Magnolia Beach (Texas) for a week or so before we start the trek up to Nova Scotia. 

[Geronimo John]

On 11/9/2024 at 4:56 AM, Sully said:

over heated the car breaks to the point that we were seeing smoke.  The breaks never faded but it was a very concerning situation.

What did you smell when you circled the Audi after overheating the brakes?  If is was an oil smell, then Audi Tech is likely right.  Did he inspect the tail pipe for black oily soot?  Another easy test to narrow down the culprit.

But if you smelled burnt brake dust, then the brake pads have glazed and the brake peddle force increases substantially to get any more braking.  If you brake peddle force was significantly higher than normal, then most likely your brake pads should be replaced.  Did the Audi Tech inspect the brake calipers?  Were they crazed, cracked or burnt?

The Audi Q7 can have a 4, 6 or 8 cylinder engine.   Also many different transmissions too.  What does your TV have?  Makes a huge difference when going up/down serious grades.

GJ

[jd1923]

On 11/10/2024 at 9:07 AM, Sully said:

Audi shuts off fuel and ignition when you take your foot off the accelerator.

In addition to @Geronimo John’s comments/questions…

There is no such thing as the above quoted statement. Any and all combustion engines need fuel and ignition even at idle let alone when “the engine at 4 to 5k rpm downhill for an extended time.”

This is not what a trained Audi tech would say. Something was lost in the translation.

Forcing your gas engine in gear to brake 12+ LBS is causing your engine oil leaks and you need to get your TV and TT brakes dialed in so not to further harm your Audi engine and drive train, worse if your Q7 is a Quattro (AWD) which can cause harm to CV axles, seals and more. Only diesel engines with engine brakes should be used for braking. Gas engines with manual transmissions can assist some, automatic transmissions not, unless you want to damage them too!

Lastly, smoke from the brakes in the front wheels is quite different from residue oil burning, coming out of the tailpipe behind the vehicle. One you would see from the windshield, the other would be noticed in the rear view mirror.

Not trying to be an a$$ here. This is the stuff that adds to frequent highway fatalities! Worry about your setup before your AZ trip. Read the post I linked above and dial in your brake controller, check your brake system down to the brake fluid.

[Mike and Carol]

On 11/10/2024 at 10:07 AM, Sully said:

Audi shuts off fuel and ignition when you take your foot off the accelerator. 

 

10 hours ago, jd1923 said:

There is no such thing as the above quoted statement. 

Agree.  If he added “when stopped” it would be accurate.  Our Audi SQ5 shuts off the engine whenever we stop.  I can override it, which I usually do because I find it annoying and don’t like the short lag when it starts back up after the traffic light turns green.

[jd1923]

3 hours ago, Mike and Carol said:

Agree.  If he added “when stopped” it would be accurate.  Our Audi SQ5 shuts off the engine whenever we stop.  I can override it, which I usually do because I find it annoying and don’t like the short lag when it starts back up after the traffic light turns green.

It's good there is an option to turn off. I've rented cars that do that and cannot stand that at lights and other intersections. I would tap the gas to get the engine ready.

[katanapilot]

Modern fuel injected gas engines absolutely shut off fuel when the throttle is lifted and the vehicle is coasting.  With the torque converter locked up (on an automatic) the engine is driven by the wheels.  Do a little homework and you will find this to be true on many vehicles.

Here is an article from 2014 - https://newatlas.com/bosch-start-stop-coasting/30380/

Edited November 13 by katanapilot

[Geronimo John]

On 11/12/2024 at 7:01 AM, jd1923 said:

It's good there is an option to turn off. I've rented cars that do that and cannot stand that at lights and other intersections. I would tap the gas to get the engine ready.

Warning:  This post boarders on becoming a rabbit hole discussion!

OIL PRESSURE:

Most modern engines are designed with the crank shaft providing the power to pump oil.  This can be by direct connection, a belt or by gears.  So generally speaking if the motor is turning it's getting oil from the sump.  However, some 1.0, 2.7 and 5.0 Fords are among exceptions, so check out yours to be sure.

My 3.5 EB oil pump is crank driven.  So my concern is not with long down-hill runs and the engine not getting lube oil.  It is with the auto start stop system, especially when towing.  Powering up mountains with Ollie puts a LOT of heat into the engine block and especially the turbo's.  If you shut off cooling water and oil, you will "bake your turbo's" and other parts as well.  It is nearly always wise when towing, or off roading, or any other high power activities to let your vehicle engine run for a period of time before shutting it off.  This is necessary to allow that latent heat to be transferred to the atmosphere.  

Some say that the period of time is when the aux fans turn off.  This may be the right answer for their vehicles.  I try to let mine run at least 7 - 10 minute after a long hot run.  And don't ask what I think about the auto on/off systems.........

ENGINE SMOKE WHEN DE-ACCELERATING:  Carbureted Engines

Not knowing which Audi engine is in play limit's my thoughts to "glitter generalities":

Carbureted engines when cycled between high power and coast settings OFTEN cause the crankcase pressure to spike downward.  If you have an ole fashioned crankcase manifold gauge you would see it go to a very high vacuum setting.  True statement that confuses many.  Said in simpler English the air pressure in the engine at full throttle for a non-turbo/super charged engines is just a bit lower that STP conditions.  But when those big 4-bbl carburetors slam closed (Coasting), the air moving through the intake system gets sucked into the intakes. and it can't get much from the intake system to replace it as the carbs are closed down.  So your vacuum gauge reading goes down in PSI towards zero.  

(For the Pro's:  I'm not even going to try to discuss absolute vacuum concepts here.)  

So if the intake head is approaching a near perfect vacuum (Like not much air there because it is all sucked out with no intake air, THEN the crankcase below the pistons gets oil vapor sucked up past the pistons and into the combustion chamber... where it gets pushed out the tail pipe.  This problem was generally ameliorated by a simple throttle return spring/cam.  If the carb can't slam shut quickly, the intake can't go way low pressure mode and little oil vapor gets sucked past the rings and out.

 

ENGINE SMOKE WHEN DE-ACCELERATING:  NPN-Carbureted Engines

For the Ford Ecoboost, and many other engines with turbo's, they pressurize the air intake system.  The air pressure is modulated by  a wastegate and throttle body.  Unlike most carbureted engines, they have a PCM that manages the process and a key element of that process is the fuel injection system.   For the Eco Boost with 10 speed transmissions, downhill pretty much is a walk in the park.  Virtually all of us use our tranny to spin up the Ecoboost vs. glazing our brakes going down hill.  I just ensure that the I keep the RPM's down to about 4500 or below.  Ford says 5,000.    

For more info on this here is a good thread:   

https://www.thehulltruth.com/trucks-trailers/964289-eco-boost-10-speed-iengine-brakingn-tow-mode.html

GJ

Edited November 14 by Geronimo John

[jd1923]

On 11/12/2024 at 7:04 PM, katanapilot said:

Modern fuel injected gas engines absolutely shut off fuel when the throttle is lifted and the vehicle is coasting.

Not on tow vehicles! Anybody with an F250/350 have this Bosch system? How about a new model Dodge Ram or those here with the GMC Duramax and 10-speed Allison.

If any Oliver Owners reply with a Yes, then I will do “a little homework.”

I would say, if the Audi Q7 has such ignition system it is NOT a proper tow vehicle. Not one I would use to tow in the mountains where we live! Bad enough a small car turns engine off at a stoplight (green deal cr@p). My truck, and any truck I will own, does not and will not cut fuel and ignition when I’m descending an 8% grade, no way!

Smoke, reburn of fuel forced by engine turning in gear downhill, due to no ignition current, wow bad situation. Towing with a car designed for suburban driving! I could tow better with our GX470 but prefer an old-school diesel for power, control and safety! 🤣

[Geronimo John]

It does save fuel!

Suspect that the 3.5 EB's have it as well.  

GJ

Edited November 14 by Geronimo John