Turbocharger cool down time

[Rick7576]

I have a 252 with a TSIO 360 mb1 engine. Recently a Slick Mag. with only 170 hrs. (new not rebuilt) crapped out on me. I was on the ground doing a standard pre takeoff mag check. The right mag was totally dead.  I discovered while trouble shooting the bad SLICK mag. that with the eng.RPM around 1000-1200 that the TIT would drop about 50*F in the 2-3 seconds that the eng. was spinning down. (the bad SLICK mag was not sparking on any cylinder, so just cool air running through the eng. and turbo). after 2-3 checks on bad mag the TIT was well below 800*F. The CHT were all below 350*. Usually after a flight it takes          3-5 min for eng to cool down.

So here's the question?   If in the future after a flight what harm if any is there  to turn off both mags (at 1000-1200 RPM) for a couple of seconds 2 to 4 times to get the TIT below 800*. then shutting the eng down the normal way by pulling the mixture. I think this can save 3+ min of idle cooling. 

[DonMuncy]

The best information I have seen (from the highly instrumented data of the guys at GAMI) is that the turbo temperatures are actually lowest at landing. The taxi time and "supposed" cool down time actually warms it back up a bit. 

[Will.iam]

I agree with Don on this my lowest temp is on landing rollout. What is your idle rpm? Mine at 750 yields tit of less than 750 degrees and at 650 rpm the tit will go below 700 degrees eventually. If I do an engine ground run up whether checking max fuel flow or max RPM then I do a 5 min cool down to get the heat out of the turbo and the turbo rpm’s down to idle speed. I also after pushing the airplane into the hanger in warmer months put a industrial fan in front of the airplane to help wick away the heat so that there is less time of the components being higher than 250 degrees and heat stressing the oil. 

[RobertGary1]

I sometimes fly a t206H for an operator that insists on waiting for a certain tit before shutdown. Sitting there idle makes it warmer than landing. 

[Schllc]

I second both of these, I usually try to shut off as soon as possible after my taxi to the hangar.  Sitting there idling never seemed to lower the temp significantly.  
It makes sense that landing phase is the coolest because of low power, rich mixture and high airflow. 

[N201MKTurbo]

I have read the the RAJAY turbo doesn't need any cooldown because of its double spool bearing.

[kortopates]

Consider the cool down starting when you pull back the power to land and long over after you taxi away to parking. Also i would avoid running on one mag, the practice is more likely to foul one of the bottom plugs. But do aggressively lean as part of your after landing checklist.


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[jlunseth]

I second what Paul said. I have the TSIO-360-LB in a 231. I have never done anything to cool down the turbo except to taxi in after landing and shutdwon. The engine, which has a Conti TBO of 1800, currently has 2380 hours and since it is 20 years old, will be replaced with Factory New this Year. My turbo was last OH’d at about 700 hoiurs, so it is at roughly 1700 hours since OH  on the turbo. I don’t know, maybe mine was a better that average OH. Either that, or turbo cooldown is an OWT. You do need to lean aggressively on the ground but that has very little or nothing to do with the turbo.

Edited January 7, 2023 by jlunseth

[A64Pilot]

First EGT is what heats a turbo, but a turbo has significant mass and it takes time to cool down, a short interval doesn’t do anything. Quantity of heat also is relevant, by that I mean the same EGT at low RPM doesn’t have nearly the heat energy as much more gasses flowing through at the same temp, an example is that live steam at 100C will burn you much more severely than boiling water at 100C, so it’s not as simple as looking at egt and inferring turbo temp.

Unless your measuring the temp of the center section and the hot end of the turbo you don’t have any relevant data.

What we are trying to prevent primarily is coking in the center section when the heat from the hot side soaks the center section and gets it hot enough to break down and oxidize the oil. Ball bearing turbos can tolerate more coking before failure than sleeve bearings, but neither is immune.

This is another case where you can choose to believe someone who has no dog in the fight, or the actual manufacturer who has a reputation and warranty to uphold, but ask yourself why would any manufacturer be so adamant to recommend a procedure that’s not necessary or extends their products lifespan?

But finally is a few minutes so important that you can sit there for that time? It usually takes me that long to clean up the cockpit and put everything away anyway, so what are you saving by skipping the cool down?

 

[rbp]

In the Bravo, once I'm ready to shut down, I set the power to idle -- no reason to put *more* power into the engine. then I watch the engine temps -- EGT of #3 (the hottest cyl) and oil temp -- once the temps have stabilized, shouldn't the (entire) engine be as cool as it can get and not require any more time? note that this takes anywhere from 3-5 minutes depending on the taxi time and grade (my home airport has a slight grade up to the hangar and therefore more power). 

[Fly Boomer]

1 hour ago, A64Pilot said:

But finally is a few minutes so important that you can sit there for that time? It usually takes me that long to clean up the cockpit and put everything away anyway, so what are you saving by skipping the cool down?

It's not the time.  It's the fact that engineers instrumented a turbo, and demonstrated that the "cool down" actually makes it hotter.  As pointed out above, instrumentation shows that the turbo is coolest during the rollout after landing.

[DonMuncy]

I hate to belabor the point, especially as it is of little consequence to me how other people operate their engines. But I think the concept is fairly important. Ordinarily, I defer to the recommendations of manufacturers of equipment, as they are usually in the best position to have superior knowledge about the things they make. But sometimes new technology or just superior attention to details, can over-ride that belief. Anyone who has seen the equipment and instrumentation at GAMI would have a hard time ignoring the data they are capable of providing. 

My point is, that it is wise to critically examine information and recommendations presented to us, as aircraft owners, and consider other ideas and conclusions. Especially if the original information available has been in existence for a long period of time. After all, if we were to blindly follow the instructions we are given, we would still be operating our engines at 50 degrees rich of peak EGT; about the worst possible place for engine longevity.

[A64Pilot]

GAMI’s instrumentation is irrelevant, service history has shown for decades don’t cool down and you’ll eventually damage the center section bearings and it’s immediately apparent on tear down because of the coked oil. Turbos that have been properly cooled down show no coking at overhaul.

But I’m certain GÁMI has no new ground breaking instrumentation, but they market well.

I am also sure that Hartzell or Continental if shown evidence that the cool down wasn’t necessary would remove the requirement, I don’t think anyone particularly enjoys a 5 min cool down, and removing it it would make turbocharging even more attractive, they have no reason to require a cool down if it’s not necessary and every reason to remove it if they could. 

You cool down farm equipment, construction equipment, OTR trucks and until water cooled centersections were used in automotive applications, pickup trucks and cars too if you wanted them to last. Water jacket around the center section prevents the thermal bloom the centersection experiences on shut down with out a cooling period.

You also cool down turbine engines for similar reasons. Don’t cool down a Garrett and the shaft will warp and seize the engine for hours

Hartzell and or Continental may come out tomorrow and say cool downs are no longer necessary, but until they do, especially if there is any warranty I suggest you cool down, if nothing else it’s not doing ant harm. 

A turbo is like a cast iron skillet just because you took it off the red hot stove a couple of minutes ago doesn’t mean it’s not still hot

[Schllc]

I can only speak for myself, but I was not arguing the need to cool down the turbo.  What I was saying that from landing phase, to taxi is usually at least 15 min and when I have stopped to cool down, the tit usually only rises at a certain point. Leaning can reduce this, but even at that point it’s a diminishing return. 
What I was saying is that after that period of default cool down, I don’t see the value of running the engine for any additional time when it only seeks to elevate or keep the temp static. 

[A64Pilot]

If you meet the POH cool down requirements taxiing, then your fine, but it’s not just TIT, or TIT would be called out in the procedure, if yours is, then of course follow it.

It’s actually an engine power output and time. I don’t pretend to know every POH requirement so if yours says maintain a TIT below X number of minutes then of course that’s all you need to meet. But you need to comply with the POH.

But you guys are of course going to do whatever you want to, I don’t understand this belief that the manufacturers are fools.

Joe Brown owns Hartzell, his company didn’t design or build Hartzell Turbo’s he bought the company.

I know Joe Brown well, we aren’t hunting buddies and we don’t send each other Christmas cards, but I’ve done business with him for years.  I know him well enough that I’m certain if he didn’t need to cool his Turbos he would publish the alternate procedure and market the fact that Hartzell’s turbos are so superior they don’t need cool downs.

He has the secret sauce, he’s bought many companies that couldn’t make ends meet and made money from them, and he’s good to his employees too, so he’s doing it not by abusing them.

I don’t think I have ever taxied for 15 min myself, but if you can taxi that last however minutes at the spec RPM, then  you’re in. I don’t think the requirement is to not be moving.

For what these things cost, why would anyone not want to follow the directions?

[Bolter]

Does anyone have the link to GAMI cooldown data and tests?  @DonMuncy

[LANCECASPER]

16 hours ago, A64Pilot said:

For what these things cost, why would anyone not want to follow the directions?

Does that mean that M20M owners should follow the POH and run at 1750 TIT and go with the redline of high 400's on CHT? The POH clearly was wrong since owners were getting 200 hours on the cylinders.

I vote that we listen to Mooney owners who have actually owned Turbo Mooneys like @DonMuncy and @jlunseth and many more that have found that sitting there for 5 minutes actually raises TIT.  Since they've learned better information they use that and they've made it to and beyond TBO without cooking a turbo. 

There was a time when the world's experts believed that the earth was the center of the universe and that everything else revolved around it. A few people who doubted that and expressed their doubt were considered heretics. Better information came along and eventually the heretics were proven correct . . .  after they had been put to death. When I first heard around 1997 that sitting there at idle in my new M20M Mooney for 5 minutes was crazy since it was doing the opposite of what I was trying to do I thought that person was nuts, even though he had flown turbo charged airplanes almost as long as I had been alive. But I respected the person and started watching my TIT and sure enough there was something to what he was saying. I began asking around and at that time most people said you just had to do it that way (sit there) . . just because. Today informed people know better since there is much better instrumentation on most panels. On 4 turbo Mooneys and one turbo Piper in the past 25+ years since then I haven't sat there and let the temperatures rise. I do sit there and watch the TIT drop until it hits it lowest point after taxi and then as soon as it bottoms out and starts to go up a degree I shut down. That usually takes between 10-20 seconds depending on time of year. I have not replaced a turbo on any of those airplanes. 

[Schllc]

1 hour ago, A64Pilot said:

But you guys are of course going to do whatever you want to, I don’t understand this belief that the manufacturers are fools.

I have read my POH cover to cover no less than 12 times.  I actually read a lot, and I’m pretty sure I understand my aircraft about as well as anyone can, but I still don’t know everything and I am ok with that…

My POH says cooldown is 5min at 900rpm and taxi can be included.   

Is it necessary to suggest no one else reads the instructions or understands their aircraft?  
Condescension is a very ineffective means of persuasion. 

[Guest]

In almost 40 years of maintenance, I can count on one hand (with fingers to spare) the number of turbocharger failures across a wide variety of airframes and pilot techniques. I believe that as long as you don’t do a full power run and then immediately shut the engine off, a turbo will live a long life.

[Fly Boomer]

2 hours ago, Bolter said:

Does anyone have the link to GAMI cooldown data and tests?  @DonMuncy

For me, it was just spoken word in Ada -- no document.

[M20F]

14 hours ago, M20Doc said:

In almost 40 years of maintenance, I can count on one hand (with fingers to spare) the number of turbocharger failures across a wide variety of airframes and pilot techniques. I believe that as long as you don’t do a full power run and then immediately shut the engine off, a turbo will live a long life.

This would be the correct answer in my book.  The internet + engine monitors make people way over think things.  

[N201MKTurbo]

We do seem to spend a lot of time on this forum talking about the things that aren't problems and sometimes ignore the real problems.

[aviatoreb]

17 minutes ago, N201MKTurbo said:

We do seem to spend a lot of time on this forum talking about the things that aren't problems and sometimes ignore the real problems.

My father used to have a joke for that:  "Other than that Mrs Lincoln, how was the play?"

[Rick7576]

Well Boys & Girls 

Thanks for all the input. happy new year, be SAFE and healthy    Cheers Rick

[Fly Boomer]

7 minutes ago, Rick7576 said:

Thanks for all the input. happy new year, be SAFE and healthy    Cheers Rick

Rick,
Happy new year to you as well, but you didn't weigh in on the topic at hand.  I didn't look up your registration number, but it seems likely that you have a 252.  What do you do after you reach your destination on the airport after landing?  Do you do a turbo "cool down" (which likely adds heat), or do you shut down after taxi?

Also, how many hours are you getting on a turbo before overhaul?