Turbocharger information that was a bit alarming...

Montanaman

Montana/Arizona
:
2018.5 CX-9 AWD GT
So I've got my 2018 CX-9 GT AWD loaded up for the 1300 mile trip back to Montana and since I am towing a small trailer with a loaded top box (that should insure some good gas mileage...NOT). I thought I should crack out the owners manual to double check the GCWR and other load limits to be safe.

On the previous page something caught my attention (Page 3-55 in the US owners manual). It says: "Caution. After driving at freeway speeds or up a long hill, idle the engine for 30 seconds before stopping it. Otherwise, the turbocharger could be damaged" .

Wow. Did not know and that is a pretty serious sounding warning. We've only had the car for 3 months and have not done any long hot trips on the freeway but several short ones and I turn the engine off as soon as I stop (like most people). So I guess I better remember this little tidbit.

So again according to the owners manual you should leave the motor run for awhile after freeway driving or you could "damage the turbo" which I am sure would not be cheap to replace.

Thoughts? Anyone else doing this?
 
This sounds like a flashback from the 80s. Thought that was history. Maybe it's just CYA for Mazda.
 
Its a common practice for me to let the engine idle for a minute before shutting down (and I have the 3.7). Lets those hotspots normalize with the rest of the gang inside.

The turbocharger gets bombarded by hot exhaust and can get very hot (especially on higher RPMs or heavy load). Shutting them down suddenly when can cook the stagnant oil lubricating its bearings (compared to a flowing oil when engine is running). Coked oil fills bearing chamber, oil does not get to the bearings while the turbine is spooling down or next time you start the engine, the rest is history.

Trivia: Aircraft engines need at least 5 mins idle before you can shut them down.
 
Its a common practice for me to let the engine idle for a minute before shutting down (and I have the 3.7). Lets those hotspots normalize with the rest of the gang inside.

The turbocharger gets bombarded by hot exhaust and can get very hot (especially on higher RPMs or heavy load). Shutting them down suddenly when can cook the stagnant oil lubricating its bearings (compared to a flowing oil when engine is running). Coked oil fills bearing chamber, oil does not get to the bearings while the turbine is spooling down or next time you start the engine, the rest is history.

Trivia: Aircraft engines need at least 5 mins idle before you can shut them down.

This has been SOP for over 12 years with my CX-7; it was just sort of a common sense best practice.
 
Wow. I've owned 34 cars from Vega's to 911's and I've never heard of the practice. Many were turbo's. If it's true than that message needs t be a lot louder.
 
This has been SOP for over 12 years with my CX-7; it was just sort of a common sense best practice.

Yep, standard procedure. Some people install boost timers on their cars to help with this, as the boost timer keeps the ignition on for a set amount of time after you've keyed off the car.

Fair point to mention (and good on you Montanaman for reading the manual! You keep people like me in work :p). My dad bought a 2.0T Equinox last year, his first turbocharged car, and he didn't know about that tidbit until I mentioned it to him the other day.
 
274 nailed it. It's all about the heat. Think of a long, hot, hard climb on mountain freeways, then you pull into a rest stop. The oil needs to continue to flow for a short time to carry the high heat away.

A turbocharger is a gas turbine on the same shaft as a centrifugal air compressor. The gas turbine is powered by the heat in the exhaust gas. The hotter the exhaust gas, the better, faster, more powerfully the gas turbine runs, and the more air it can pump into the engine's induction system.

So, a brief idle period after a hot run is a very good idea. Synthetic oil handles high heat better, so that's a good idea. (Where space permits the turbo can have larger oil spaces to help it resist overheated oil. The VW engines of a few years ago were an example of doing it wrong--not enough room and coked turbos.)
 
On my wife's BMW there is are two heat-activated auxiliary pumps, one that keeps oil circulating through the turbos after the engine has been shut down, and the other that does the same with coolant. Plus the fan keeps running. In BMW's case it is partly because both turbos are on top of the engine in the V between the two cylinder banks, so there can be tremendous heat build-up right under the hood immediately after switching off.

But it has always been good practice with any turbocharged engine to allow the turbo a few seconds to cool down before switching off unless it has BMW-style auxiliary lubrication/cooling. 'Coking' of oil in the turbo's shaft can lead to premature failure. That is probably why Mazda recommends such frequent oil changes.
 
Does anyone have direct experience of anyone coking their turbo in this century? I wonder if it's more ancient anecdotes than a real issue with modern turbos. It surely did happen to some early ones, but with modern designs and oils, is it still a danger?

My own experience was 80K on a 2004 Forester turbo. I never let it idle before ignition off, and it held up fine. Maybe I was just lucky, but there are a lot of turbos out there, and I'd bet most owners don't take the time.
 
Does anyone have direct experience of anyone coking their turbo in this century? I wonder if it's more ancient anecdotes than a real issue with modern turbos. It surely did happen to some early ones, but with modern designs and oils, is it still a danger?

My own experience was 80K on a 2004 Forester turbo. I never let it idle before ignition off, and it held up fine. Maybe I was just lucky, but there are a lot of turbos out there, and I'd bet most owners don't take the time.

I think it depends on how you drive it too. This is my first turbocharged vehicle, and when I'm just going to the grocery store or out to eat or whatever, I always shut down as soon as I get there. If that's how you drive it, then I don't think there's any risk. But if you're operating the vehicle in specific conditions, the risk of damage is higher, which is why it's stated in the manual.
 
This came up a while ago. Often, when you drive slowly into your neighborhood and idle a little bit before shutting it off, that is good enough.
 
Thanks for the feedback. Color me naive on this one. Never heard of it and it sounds like its more of a possibility for damage that just a Mazda covering their ass. It also sounds like something that should have been improved to the point where it's a non -issue. And lastly it sounds like something that should be more than a foot-note in the owners manual. I'm glad I know as we do some heavy highway miles but the chances of my wife ( really her car) remembering to wait 30 seconds after she parks to shut the car off are slender.
 
I knew cool down periods used to be a thing with turbos back in the day, but today's turbo engines are designed with far better cooling systems. Still, I've been aware of the idea that if you were to really push your engine using a lot of boost, not to shut it down immediately following that.

What I try to do is to drive more leisurely the last couple of minutes up to my destination. What I find odd about the passage in the owners manual is where it states simply driving on the freeway. Driving normally on the highway rarely sees the turbo spooling up except for hard passing. I guess if your destination is immediately off the highway but even then the engine is at a normal operating temp.

Either way, I doubt this is a critical practice in modern cars. If it were, it wouldn't be buried deep in the owners manual that almost no one sees. Notice the first person has only now found this 3 years after Mazda's turbo came out. I also don't think Mazda would have sold me a 100K mile extended full coverage warranty if this practice was critical to engine life.
 
Thanks for the feedback. Color me naive on this one. Never heard of it and it sounds like its more of a possibility for damage that just a Mazda covering their ass. It also sounds like something that should have been improved to the point where it's a non -issue. And lastly it sounds like something that should be more than a foot-note in the owners manual. I'm glad I know as we do some heavy highway miles but the chances of my wife ( really her car) remembering to wait 30 seconds after she parks to shut the car off are slender.

This is most likely a non-issue and Mazda is just doing some CYA...

Almost all OEM turbos nowadays have water cooled center cartridges (where the bearings are). Back before this was a thing, the turbo bearings relied on the oil only for cooling. This is far from ideal, as oil has very poor cooling properties (specific heat) and the flow rate is usually pretty low (the bearings don't need a lot of oil). As a consequence, the oil in the turbo could get quite hot, particularly if you ran the engine hard then shut it off. In that circumstance, you would cook the oil that was stagnant in the turbo bearings.

A water cooled turbo has engine coolant circulating through the bearing housing. This keeps the bearings and oil a lot cooler during operation. Also, even in the case where you run the engine hard then turn it off, the water in the turbo will boil, which helps keep the temperatures down. I'd still recommend taking it easy on the engine in the minute or so before shutting it off to let things cool off, but this is nowhere near the issue it used to be.
 
Does anyone have direct experience of anyone coking their turbo in this century? I wonder if it's more ancient anecdotes than a real issue with modern turbos.
"According to court documents, the settlement affects 1997-2004 Audi A4 models and 1998-2004 VW Passat models with 1.8-liter turbocharged engines.

"The engines were prone to oil sludge from coking deposits even when maintained according to the automaker's recommended maintenance intervals and oil-quality specifications, court documents show."


Read more: https://autoweek.com/article/car-news/vw-cover-maintenance-costs-sludge-damaged-engines#ixzz5jebDkzpK
 
"According to court documents, the settlement affects 1997-2004 Audi A4 models and 1998-2004 VW Passat models with 1.8-liter turbocharged engines.

"The engines were prone to oil sludge from coking deposits even when maintained according to the automaker's recommended maintenance intervals and oil-quality specifications, court documents show."


Read more: https://autoweek.com/article/car-news/vw-cover-maintenance-costs-sludge-damaged-engines#ixzz5jebDkzpK

Sludging isn't isolated to turbo motors, though. Toyota had problems with some normally aspirated V6's a few years back.

The VW issue was certainly related to the turbocharger overheating the oil, but they also had small oil sumps. The "fix" was to use a bigger oil filter that held more oil. Solid German engineering...
 
This sounds like a flashback from the 80s. Thought that was history. Maybe it's just CYA for Mazda.

Total flashback... I remember my '79 Mustang Cobra with 2.3L turbo and racing my buddy in his Dodge Daytona Z. All sorts of parts were glowing red (no kidding) after such antics (including exhaust side of turbo, front rotors... ahhh, Chrysler).

In those days I did do a cool down as the turbo was oil-cooled only and I would do a cool-down run but I think @jal142 gets this right. Most likely CYA language in the manual, and really, only 30 seconds and not 5 min means as you coast off your exit ramp and turn into a motel or gas station, you've done your 30 seconds of cool down.

I wouldn't sweat it-- I saw that in the manual and had a flash of concern myself. When you think about it, these engines are not frying themselves left and right, so I think we're ok.

(Can anyone verify that our turbos are liquid-cooled? I'm less then a month in on ownership and haven't done my deep dive into the engine bay to check things out.)
 
It is true that any turbo that has been used in an effort reaches extreme temperatures, modern turbos will manage this a lot better than older ones but as anything that is heated up has to be cooled. Usually when ur arriving ur destination one slows down and the turbo has time to cool down. If this is not the case and u have been driving quite fast or towing , the recommended thing is to let ur turbo cool down while he engine is turned on for a little while
 
Yep, standard procedure. Some people install boost timers on their cars to help with this, as the boost timer keeps the ignition on for a set amount of time after you've keyed off the car.

Fair point to mention (and good on you Montanaman for reading the manual! You keep people like me in work :p). My dad bought a 2.0T Equinox last year, his first turbocharged car, and he didn't know about that tidbit until I mentioned it to him the other day.

"Turbo timers"- no such thing as a boost timer. I'm surprised this is still needed for modern turbos- even on my heavily modified Supra and EVO (years ago), turbo timers were useless with water cooled turbos.
 
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"Turbo timers"- no such thing as a boost timer. I'm surprised this is still needed for modern turbos- even on my heavily modified Supra and EVO (years ago), turbo timers were useless with water cooled turbos.

Right, minor oversight. Thanks for correcting.

I'm not so sure it's "needed".. probably more of a CYA thing for Mazda.
 
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