Machines with turbos- do you let them idle before shutting down

[JerryMT]

I have a 7060 which has a turbo. I have always been told to let machines with turbo's idle for a while so the turbo can slow down and still get oil.

Is this still a big deal?

I have a guy that helps me and he just turns the machine off because that is what he has been doing for 60 years.

My NH TD95D has a turbo and the recommendation in the owners manual is to let it idle at 1200 rpm for one minute after full power operation to prevent turbine rubs since the outer case cools more quickly than the turbine wheel. I very seldom operate at full power but I let any engine idle, NA or turbocharged, before I shut down.

 

[JerryMT]

A. Venturi effect on the exhaust pipe produces NO measurable pressure at the turbo and certainly not enough to make it spin. This is a myth and complete misunderstanding of a turbo and the physics of pressure. If you think it does please provide a reference supporting your belief. Physics, its not just a good idea its the law. Next question: What operating condition allows you to go down the road without the engine running?

B. Synthetics do help, as the base stock cokes at higher temps than dino based oils. However according to mobil 1, there is still a risk that when the oil stops moving through the turbo, i.e. shutdown, that some of the friction modifiers and stabilizers can coke, causing deposits. Ultimately, according to most oil manufacturers and several academic papers, the best way to prevent coking issues is to let the turbo cool under engine idle, to less than about 300 degrees. No, bs, no myth, no strange voodoo. If you want to protect your turbo, it has to be shut down at a temp below the coking temp for the oil your using.

Going down the road without the engine running is the case of trailering a tractor.

New Holland's owners manual on my TD95D recommends taping or otherwise closing the exhaust pipe when trailering this tractor. When the engine stops invariably valves stay open allowing the pressure differential from the stagnation pressure caused by forward velocity and the lowered base flow pressure on the exhaust pipe exit to support flow through the engine and the turbo. In general, the higher the towing speed, the bigger the differential Most of these engines use the main engine oil pump to supply oil to the turbo bearings. With the engine not running there is no oil supply. If they windmill without a bearing oil supply long enough they can be damaged.

It's not a myth. It simple aerodynamics.

 

[adventure bob]

Um, its not aerodynamics...its gas law. And a couple of really old physicist, guys like Bernoulli figured this out way before tractors. While I don't doubt your manual has a statement as such, lets walk through your theory for discusion.

If I understand you correctly, when towing, there's an increase in pressure on the intake side that flows through the engine, through the open exhaust valves ultimately increasing pressure on the inductor side of the turbo. That air pressure, I'm assuming is coming through the air intake. At the same time there's a pressure drop on the exhaust side of the turbo by airflow over the exhaust tip. I'm assuming this is the venture effect you referred to earlier. This pressure differential is enough to cause the turbo to spin fast enough to potentially cause bearing damage over time.

Do I understand the logic correctly? I want to make sure were at the same starting point for discussion. And this should be a discussion that informs members of some factual arguments that allow them to make informed decisions. If I have that right and your willing to discuss openly post up.

 

[JerryMT]

Um, its not aerodynamics...its gas law. And a couple of really old physicist, guys like Bernoulli figured this out way before tractors. While I don't doubt your manual has a statement as such, lets walk through your theory for discusion.

If I understand you correctly, when towing, there's an increase in pressure on the intake side that flows through the engine, through the open exhaust valves ultimately increasing pressure on the inductor side of the turbo. That air pressure, I'm assuming is coming through the air intake. At the same time there's a pressure drop on the exhaust side of the turbo by airflow over the exhaust tip. I'm assuming this is the venture effect you referred to earlier. This pressure differential is enough to cause the turbo to spin fast enough to potentially cause bearing damage over time.

Do I understand the logic correctly? I want to make sure were at the same starting point for discussion. And this should be a discussion that informs members of some factual arguments that allow them to make informed decisions. If I have that right and your willing to discuss openly post up.

This is clearly a fluid dynamic issue not a gas law issue. When someone says "gas law" to me I think of the equation of state, Boyles Law, etc which deal with gases that are not in motion at the macro level. Bernoulli's Equation is a relationship based on fluid in motion and not a "gas law", per se. Further , I don't believe I used the term "venturi effect".

Your statement is essentially correct. The front of a the engine is a stagnation region i.e Po = ps + 1/2* rho *V^2 where Po is the stagnation pressure, ps is the static pressure or the ambient pressure in this case, rho is the sir density and V is the velocity. (At the speeds we are talking about, compressibility isn't a issue so we can consider the air to be incompressible.)

The static pressure at the exhaust tip might be as high as ambient or less due to the effects of the base area of the tube. Of course the orientation of the tube exist relative to the freestream velocity effects this local pressure but let's keep this simple. So worse case you have at least 1/2* rho*V^2 across the engine/ turbo that can windmill the turbo. The higher the velocity the higher the pressure differential.

The crucial point is that an intake and exhaust valve have to be open on the same cylinder which occurs during valve overlap. So windmilling of an unlubed turbo during trailering can not be ruled out.

 

[greenacresnorth]

This is clearly a fluid dynamic issue not a gas law issue. When someone says "gas law" to me I think of the equation of state, Boyles Law, etc which deal with gases that are not in motion at the macro level. Bernoulli's Law is a relationship based on fluid in motion and not a "gas law", per se. Further , I don't believe I used the term "venturi effect".

Your statement is essentially correct. The front of a the engine is a stagnation region i.e Po = ps + 1/2* rho *V^2 where Po is the stagnation pressure, ps is the static pressure or the ambient pressure in this case, rho is the sir density and V is the velocity. (At the speeds we are talking about, compressibility isn't a issue so we can consider the air to be incompressible.)

The static pressure at the exhaust tip might be as high as ambient or less due to the effects of the base area of the tube. Of course the orientation of the tube exist relative to the freestream velocity effects this local pressure but let's keep this simple. So worse case you have at least 1/2* rho*V^2 across the engine/ turbo that can windmill the turbo. The higher the velocity the higher the pressure differential.

The crucial point is that an intake and exhaust valve have to be open on the same cylinder which occurs during valve overlap.

Jerry if you where a chick and a red head I would totally buy you a drink after the maths throw down you just issued!!!! BAHAHAHAHA

 

[JerryMT]

Jerry if you where a chick and a red head I would totally buy you a drink after the maths throw down you just issued!!!! BAHAHAHAHA

Mike,

I was just trying to explain some thing technical that the other poster took issue with. I hope it came across as rational and informative and not as any type of put down. I certainly didn't mean it to be.
Since I'm neither a chick nor a redhead, your bar money is safe!(grin).

 

[greenacresnorth]

Mike,

I was just trying to explain some thing technical that the other poster took issue with. I hope it came across as rational and informative and not as any type of put down. I certainly didn't mean it to be.
Since I'm neither a chick nor a redhead, your bar money is safe!(grin).

I sent you and PM Jerry.

 

[JerryMT]

I sent you and PM Jerry.

Is there some secret to receiving a PM? I can't find your message, Mike.

 

[greenacresnorth]

didnt think so, it up in the top right where it says welcome (your user name)

 

[JerryMT]

didnt think so, it up in the top right where it says welcome (your user name)

Mike,
No sign of your message in my message folder. ????

 

[griffin800]

I have a 7060 which has a turbo. I have always been told to let machines with turbo's idle for a while so the turbo can slow down and still get oil.

Is this still a big deal?

I have a guy that helps me and he just turns the machine off because that is what he has been doing for 60 years.

We've got two Cat's and an MTU diesel at work and they all require a 5 minute cool down before shutting off. Not quite the same thing, these are big diesels but same deal on the turbo, they get really hot running under load, best to let them cool gently, they are quite expensive to fix.

Bill H.

 

[adventure bob]

Jerry, I take no offense by your post and look forward to a rebuttal; I didn't take it wrong or offensive. Its discussion, and discussion with math is even better. I've been a little slow in the thought process: Broke my ankle last sun and had surgery weds to pin all the pieces back in the right place. I thoroughly enjoy discussions like this; I'm a research engineer by trade. Give me a bit and Ill carry on the discussion.
Intelligent discussion, and thumbs, is what separates us from the animals.

 

[JerryMT]

Jerry, I take no offense by your post and look forward to a rebuttal; I didn't take it wrong or offensive. Its discussion, and discussion with math is even better. I've been a little slow in the thought process: Broke my ankle last sun and had surgery weds to pin all the pieces back in the right place. I thoroughly enjoy discussions like this; I'm a research engineer by trade. Give me a bit and Ill carry on the discussion.
Intelligent discussion, and thumbs, is what separates us from the animals.

Sorry to hear about your injury, Bob. Best wishes for a speedy recovery.

 

[adventure bob]

Now lets apply some basic reality to the situation to get some numbers and at least some Kentucky windage of the possibility of pressure in the intake rising enough when being towed to actually make a difference at the turbo. My argument is that there is NO pressure increase at the turbo under towing conditions.
At 60mph stagnation pressure is about 0.08 psi (p = .00002222 * v^2; p==psi; v==mph). Lets assume a 3in diameter intake pipe (on my L4060 its much smaller but Im being conservative). That puts the intake pressure at ~.43psi. Comparatively the maximum psi of exhalation by a male human (97th percentile, so optimistic) is, according to an NCBI study is about 1.3psi. If you pull your turbo off your vehicle and set up an experiment where you could blow into a tube directly attached to the inlet of the turbo I highly doubt you could spin it with this pressure, let alone .43psi. Lets talk about some assumptions that have to be agreed to before one could assume that the .43psi was actually being applied to the vanes on the turbo. 1. The intake is unrestricted and perpendicular to airflow 2 there are no losses due to friction in the intake pipe 3. that there’s no air filter in the pipe 4. The engine came to rest at perfect cam overlap and that the valves present no restriction to airflow 5. That there is no mechanical resistance at the turbo spindle to rotation 6 that the applied pressure is enough to overcome the pumping force required to spin the turbo.
If everything was perfect and all the assumptions above were true, then .43psi is actually being applied to the vanes of the turbo at 60mph on a trailer. The question I don’t have definitive answer to is: Is this enough to spin a turbo and if it is, will it spin fast enough to cause wear without oil flow? I have reached out to Holset and Garrett to see what minimum pressure is required to actually make a representative turbo spin.
We do know however that every one of the assumptions is NOT feasible and results in a drop in pressure. For example an air filter(a K&N e1460 as a conservative example, I think our tractor filters will have higher pressure drops) drops .029psi over the media when clean. Just with the air filter your now down to .40 psi. If we line up all the pressure drops over the entire intake track were looking at essentially 0 pressure at the turbine when being towed at 60mph.

 

[JerryMT]

Now lets apply some basic reality to the situation to get some numbers and at least some Kentucky windage of the possibility of pressure in the intake rising enough when being towed to actually make a difference at the turbo. My argument is that there is NO pressure increase at the turbo under towing conditions.
At 60mph stagnation pressure is about 0.08 psi (p = .00002222 * v^2; p==psi; v==mph). Lets assume a 3in diameter intake pipe (on my L4060 its much smaller but Im being conservative). That puts the intake pressure at ~.43psi. Comparatively the maximum psi of exhalation by a male human (97th percentile, so optimistic) is, according to an NCBI study is about 1.3psi. If you pull your turbo off your vehicle and set up an experiment where you could blow into a tube directly attached to the inlet of the turbo I highly doubt you could spin it with this pressure, let alone .43psi. Lets talk about some assumptions that have to be agreed to before one could assume that the .43psi was actually being applied to the vanes on the turbo. 1. The intake is unrestricted and perpendicular to airflow 2 there are no losses due to friction in the intake pipe 3. that there***8217;s no air filter in the pipe 4. The engine came to rest at perfect cam overlap and that the valves present no restriction to airflow 5. That there is no mechanical resistance at the turbo spindle to rotation 6 that the applied pressure is enough to overcome the pumping force required to spin the turbo.
If everything was perfect and all the assumptions above were true, then .43psi is actually being applied to the vanes of the turbo at 60mph on a trailer. The question I don***8217;t have definitive answer to is: Is this enough to spin a turbo and if it is, will it spin fast enough to cause wear without oil flow? I have reached out to Holset and Garrett to see what minimum pressure is required to actually make a representative turbo spin.
We do know however that every one of the assumptions is NOT feasible and results in a drop in pressure. For example an air filter(a K&N e1460 as a conservative example, I think our tractor filters will have higher pressure drops) drops .029psi over the media when clean. Just with the air filter your now down to .40 psi. If we line up all the pressure drops over the entire intake track were looking at essentially 0 pressure at the turbine when being towed at 60mph.

Perhaps you could make a system diagram to help me understand your analysis because so far it doesn't make much sense (no disrespect meant). It looks to me like your are trying to do an internal duct analysis and you really don't have enough info to make that kind of analysis.

One of the critical parameters is corrected compressor inlet airflow (W*sqrtTt/Po) through the turbo which is a function rpm/sqrtTt) that will determine the internal flow velocities which in turn determine the stagnation pressure losses. Making guesses as what these are does not guarantee a unique solution. You quote a pressure based on pipe area so it must be a static pressure. In order to determine a static pressure, you must know the airflow rate as well as the pipe area.Air filter pressure losses are generally quoted at some rated airflow and scale as deltap/q = constant ( i.e. a q = 0.5* rho*v^2). What airflow have you assumed to get this pressure drop.

My analysis showed that there was a pressure differential across the engine and turbo that was at least free stream dynamic pressure and it could be more depending on the configuration of the exhaust pipe exit. Since you cannot rule out the fact that the engine stopped with one cylinder having having overlapped valves, you could not rule out the turbo not windmilling.

Just an observation; I've see aircraft engines, large and small, windmilling with 5 mph winds. A turbo is just a small gas turbine without the restriction of a combustor. So it's easier to wind mill it.

 

[adventure bob]

why yes you have. Its the PSI over the area of object the force is being applied to. Our example 3in intake tube is considerably smaller than the aircraft engine. In a 5mph wind, if you had a 1sq foot plywood shield it wouldn't be that much of an effort (i can do the math if youd like) but a 4X8 sheet in the same wind becomes unmanageable.

 

[JerryMT]

why yes you have. Its the PSI over the area of object the force is being applied to. Our example 3in intake tube is considerably smaller than the aircraft engine. In a 5mph wind, if you had a 1sq foot plywood shield it wouldn't be that much of an effort (i can do the math if youd like) but a 4X8 sheet in the same wind becomes unmanageable.

In the case of a wind milling engine It is the flow through the engine that cause the blades to be subjected to an aerodynamic lift force that has a component in the tangential direction. if this tangential force component is greater than the internal mechanical friction (sometimes called windage) the engine will windmill. The pressure differential supports the through flow. In like manner, that's how a turbo will windmill IF there is throughflow from open valves on the same cylinder in the engine of a trailered machine.

 

[Kennyd4110]

Man...my head is spinning like a turbo...

I'll just follow the directions and guidance that's printed in my owners manual thanks...


Transporting Machine on Trailer
c CAUTION: Avoid injury! Use extra care when loading or unloading the machine into a trailer or truck.

Close fuel shut-off valve, if your machine is equipped.

IMPORTANT: Avoid damage! Transporting a machine on a trailer or on a truck bed at high speeds can result in hood or engine cover raising and possibly coming off machine if not secured.

***8226; Position machine on trailer so hood or engine cover opens from rear of trailer to prevent wind from blowing hood or cover open.

***8226; Secure hood or engine cover with existing machine locks or latches.

***8226; Secure hood or engine cover with tie down straps if no locks or latches exist.


NOTE: Use a heavy-duty trailer to transport your machine.

1. Raise implements, if installed, before driving onto trailer.

2. Back machine onto heavy duty trailer. Position machine so hood will not raise in wind while being transported.

3. Lower any implements to trailer deck.

4. Lock the park brake.

5. Stop the engine.

6. Remove the key.

7. Close the fuel shut-off valve.

8. Fasten machine to trailer with heavy-duty straps, chains, or cables. Both front and rear straps must be directed down and outward from machine. Trailer must have signs and lights as required by law.

9. Plug exhaust pipe to avoid unintended turbo spinning and damage.

 

[adventure bob]

Jerry, I think what you've stated is absolutely true, theoretically I wholeheartedly agree that theoretically it is possible. However I think I've showed mathematically that there simply isn't enough pressure at the turbo to make it spin. Even if we ignore all of the real things that are going to cause pressure drop from the intake to the turbo.
So for the sake of discussion,

1. Do you agree with the calculation of intake pressure at 60mph? if not lets discuss.
2. For simplicity, I have assumed out all of the physics that lower intake track pressure and still cannot get to enough pressure to spin a turbo. If we account for all of those the pressure will be way less than .43psi at the turbo
3. Do you agree that the tangential force is measured in psi or some other force i.e. mmH2O, inHG or whatever unit you prefer and that if there is not enough tangential force, psi, to turn the turbo then it will not turn?

 

[adventure bob]

Kenny, I realize the manual says that. no argument form me that it does. However the physics doesn't work. In the case you've listed you load the machine on the trailer backwards, implying that there's a direct airflow into the exhaust. The same math and assumptions apply except with less restrictions. So if you have a 3in straight exhaust pointing directly into the wind, your going to still get a mx of .43 psi at the turbo on the exhaust side. However you have a muffler and if you have a newer tractor more than likely a DPF between the exhaust tip and the turbo. If you go over to some of the discussions about DPF flow restriction the discussion is over cause some would have you believe that the DPF is a massive exhaust flow restriction, way more than .43psi.