Non Diesel Turbo

[Peteandsharon]

Hey guys, Just purchased a new explorer sport with the 3.5 L Ecoboost. Now that Ecoboost has dual turbos which raised a question in my mind. I asked the question on an Explorer forum and they seemed to be baffled by it. I've always accepted the line that you never turn off a hot diesel engine because of the issues of coking in the turbo. So I always waited for the EGT to get down around 300 before shutting down. My question is why you never seem to hear the same rule of thumb about these turbo'd gas engines. Nobody on the Explorer forum seemed to be familiar with the concept at all and of course my owners manual says nothing about that. Any thoughts about the difference? There seems to be some thought that water cooling the turbo gets around this issue and that's what these turbos do. If so, I'm not sure why the turbo diesels don't use the same technology.

 

[Bob&Patty]

Pete, it could the fact that diesel fuel has more oil in it than gas does that spins the turbo. The water temps normally run about 212* or a little higher on both engines. I do let my Duramax run a little if it has been running/pulling hard before I shut it down. To me it's what you think you should do....everyone has their own opinion.

 

[FiremanBill]

While not mentioned in the manuals I think it is prudent to let just about any engine idle down for a while before shutting it off. Especially if it has been working hard towing a trailer.

 

[Peteandsharon]

While not mentioned in the manuals I think it is prudent to let just about any engine idle down for a while before shutting it off. Especially if it has been working hard towing a trailer.

Yeah, with the Powerstroke I did it as a matter of course, regardless of whether I had been pulling. I used the EGT as my guide. But I tend to be old school and very conservative about those things. Better safe than sorry I believe.

 

[porthole]

The "coking" problem was a problem when most turbos did not have cooling water jackets around the bearing, gasoline or diesel.

Not unusual for a turbo to be spinning 125,000 - 200,000 RPM depending on the load.
Prior to water jackets, shutting down the engine after a heavy load could have the turbine spinning for a considerable time after shutdown. It is already hot, and the spinning turbine created additional heat without the benefit of the oil still pumped around the bearing. So, bearings overheat and the oil "cokes".

Basically the oil breaks down, forms solid deposits, blocks oil flow, bearing fails, turbo fails.

That is where the "let your turbo engine idle for a few minutes" came from.

When Chrysler first came out with the turbo charged 2.2L gasoline 4 cylinders, they were hot little engines, capable of quite a bit of power. The first versions had non water cooled turbos. It wasn't long before I was doing on average a turbo a month until the engines were updated to water cooled turbos.

Water cooling the oil helps quite a bit, even if you shutdown immediately. Although the oil is no longer being circulated, by convection the coolant around the bearing is, although nowhere near as much as with the engine running. There was at least one manufacturer that ran an electric water pump after shut down for this purpose, and those pumps were available on the aftermarket.

BTW, that convection circulation is exactly how your block heaters work. An element in the lower end of the engine heats the coolant and it slowly circulates.

Modern diesels are designed to be shut down after "normal" running. But that doesn't mean that any turbo'ed engine would not benefit from a "cool down" period.

I use a timer on my truck that allows for an approximate 2-2.5 minute run time after shutting down and removing the key.

Low grades of dino oil may "coke up" easier/sooner.
Synthetic oils tend not to coke because of the superior temperature capabilities, and the natural non coking properties.

 

[Jasonrs1319]

As Ford does not utilize an oil cooled center bearing in the turbos (they are coolant cooled) its not necessary to idle the engine to cool the turbos. There is limited possibility of coking. Not necessary to idle but I could never hurt.

 

[Peteandsharon]

The "coking" problem was a problem when most turbos did not have cooling water jackets around the bearing, gasoline or diesel.

Not unusual for a turbo to be spinning 125,000 - 200,000 RPM depending on the load.
Prior to water jackets, shutting down the engine after a heavy load could have the turbine spinning for a considerable time after shutdown. It is already hot, and the spinning turbine created additional heat without the benefit of the oil still pumped around the bearing. So, bearings overheat and the oil "cokes".

Basically the oil breaks down, forms solid deposits, blocks oil flow, bearing fails, turbo fails.

That is where the "let your turbo engine idle for a few minutes" came from.

When Chrysler first came out with the turbo charged 2.2L gasoline 4 cylinders, they were hot little engines, capable of quite a bit of power. The first versions had non water cooled turbos. It wasn't long before I was doing on average a turbo a month until the engines were updated to water cooled turbos.

Water cooling the oil helps quite a bit, even if you shutdown immediately. Although the oil is no longer being circulated, by convection the coolant around the bearing is, although nowhere near as much as with the engine running. There was at least one manufacturer that ran an electric water pump after shut down for this purpose, and those pumps were available on the aftermarket.

BTW, that convection circulation is exactly how your block heaters work. An element in the lower end of the engine heats the coolant and it slowly circulates.

Modern diesels are designed to be shut down after "normal" running. But that doesn't mean that any turbo'ed engine would not benefit from a "cool down" period.

I use a timer on my truck that allows for an approximate 2-2.5 minute run time after shutting down and removing the key.

Low grades of dino oil may "coke up" easier/sooner.
Synthetic oils tend not to coke because of the superior temperature capabilities, and the natural non coking properties.

Thanks Duane. Good information. So if I can paraphrase, with the Ecoboost gas engine it wouldn't hurt and may be a good idea to let it idle a bit but it's not mission critical and you really shouldn't hurt anything if you don't. Did I get that right?

 

[porthole]

As Ford does not utilize an oil cooled center bearing in the turbos (they are coolant cooled) its not necessary to idle the engine to cool the turbos. There is limited possibility of coking. Not necessary to idle but I could never hurt.

Not sure what you saying here.
The purpose of the bearing is to support the turbine
The purpose of oil is to lube the bearing
The purpose of the coolant is to cool the oil and turbo assembly through conduction.

Generation 1 6.7L

From the 6.7 Ford "Coffee Table Book"

Lubrication System Oil Flow

• Oil is drawn from the oil pan through the pickup tube. The oil is then routed through a passage cast into the upper oil pan then to the oil pump inlet.
  
• From the oil pump, oil is directed to the oil cooler and then to the oil filter.
  
• The main oil passage in the rear of the engine block feeds the right, left and the camshaft galleries.
  
• Right oil gallery feeds the:
  
  • – rocker arm oiling manifold for the right cylinder head.
    
  • – cam followers and hydraulic lifters on the right side.
    
  • – piston cooling jets on the right side.
    
  • – crankshaft main bearings,
    • a separate oil passage for each main bearing.
    • also used to lubricate the connecting rod bearings.
    
  • – turbocharger.
    
• Left oil gallery feeds the:

– rocker arm oiling manifold for the left cylinder head.
• An oil passage connected to the gallery going up to the left cylinder head also provides engine oil to the:
– vacuum pump.
– meshed gears of the crankshaft, camshaft and high pressure fuel pump.

– cam followers and hydraulic lifters on the left side.
– piston cooling jets on the left side.
• Camshaft oil gallery feeds the camshaft bearings.


Primary Cooling System Flow
• The primary cooling system coolsthe following components:

• – engine block
  
• – cylinder heads
  
• – engine oil cooler
  
• – turbocharger
  
• 
  – EGR cooler
  

• Coolant is drawn into the pump inletlocated in the front cover from thebottom radiator port and flows fromthe coolant pump through the frontcover to the crankcase.
  
• From the crankcase the coolant
  is routed to the cylinder heads,turbocharger, engine oil cooler andthe heater core.
  
• The coolant enters the turbocharger from a passageway in the engineblock. The coolant exits by a tubemounted on the left side of theturbocharger and goes into thewater crossover at the front of theengine.

Generation 2 6.7L


From Fords media announcement page:

• Redesigned turbo oil and cooling lines to improve sealing

https://media.ford.com/content/ford...-duty-features-improved-power-stroke-die.html

 

[porthole]

Thanks Duane. Good information. So if I can paraphrase, with the Ecoboost gas engine it wouldn't hurt and may be a good idea to let it idle a bit but it's not mission critical and you really shouldn't hurt anything if you don't.

Did I get that right?

Yes


I test drove the 2015 F150's last week, 2.7 and 3.5 Ecoboost. Impressive performance.
If I was to buy one I would do the same as I do now.
If I had worked the engine before stopping I would let it run for a minute or so.
Normal driving I would most likely just shut it off.

For me, normal means my last 10-15 seconds for the most part is a coast mode, no real load on the engine.

Now, if you are going to floor the vehicle and spool up the turbo pulling into your parking space - doesn't matter what the application, that turbo is going to spool up and would benefit from a cool down period. Even if only 10-15 seconds.

 

[porthole]

As Ford does not utilize an oil cooled center bearing in the turbos (they are coolant cooled) its not necessary to idle the engine to cool the turbos. There is limited possibility of coking. Not necessary to idle but I could never hurt.

Now that I re-read this, and the title to the thread is "non diesel", I'm guessing you are referring to the Eco boost engines???
I now nothing about the Eco's, but still think they have bearings and the bearings need to be cooled somehow.

 

[porthole]

And now since my curiosity is piqued........

Found this article on the 3.5 Ecoboost with the following comment.

The EcoBoost approach eliminates several customer worries from previous turbocharger applications. Designed for long-life reliability, EcoBoost’s turbochargers feature water-cooled bearing jackets. This architecture is designed to prevent oil “coking” that could occur in previous-generation turbochargers. The new design means that EcoBoost drivers don’t need to observe special operating precautions, such as idling the engine before switching it off. The turbochargers are designed for a life cycle of at least 150,000 miles or 10 years.

And this article on the 2015's

And like the 3.5-liter EcoBoost, the 2.7-liter’s design also incorporates reverse-flow engine cooling so the heads and turbos get cooled before the block, allowing for quicker warm-up time, better fuel and power efficiency, and overall better durability than would be afforded by conventional cooling. (The twin turbos are also oil-cooled.)

 

[Peteandsharon]

And now since my curiosity is piqued........

Found this article on the 3.5 Ecoboost with the following comment.

The EcoBoost approach eliminates several customer worries from previous turbocharger applications. Designed for long-life reliability, EcoBoost’s turbochargers feature water-cooled bearing jackets. This architecture is designed to prevent oil “coking” that could occur in previous-generation turbochargers. The new design means that EcoBoost drivers don’t need to observe special operating precautions, such as idling the engine before switching it off. The turbochargers are designed for a life cycle of at least 150,000 miles or 10 years.

And this article on the 2015's

And like the 3.5-liter EcoBoost, the 2.7-liter’s design also incorporates reverse-flow engine cooling so the heads and turbos get cooled before the block, allowing for quicker warm-up time, better fuel and power efficiency, and overall better durability than would be afforded by conventional cooling. (The twin turbos are also oil-cooled.)

Beautiful! That answers my question exactly. Thank you. So I can drive with peace of mind. But........ there is still the question of pre-Ecoboost turbo'd applications. If this was an evolutionary step to solve that concern then you would still think that it would be common knowledge among earlier turbo'd automobile applications that they needed to observe the same idling protocol. The fact that this requirement is practically unknown seems strange to me.

 

[Jasonrs1319]

Potholes I'm saying the same thing as you. The center bearing is lubricated with oil but cooling does not rely on oil flow. Coking affects the center bearing so idle turbo cooling is not necessary.

 

[JohnD]

While not mentioned in the manuals I think it is prudent to let just about any engine idle down for a while before shutting it off. Especially if it has been working hard towing a trailer.

My grandpappy told me that you should never start the vehicle and immediately take off!

He taught me to start the engine and let it run no less than 30 seconds before you take off.

I believe that this practice is why I generally get well over 100,000 miles on just about every vehicle I've ever owned without any major mechanical issues with them!

I watch people every day just jump in their cars and turn the key, and immediately take off!

And I know that a lot of them (people I know) seem to have their cars and trucks in the shop a lot . . .

 

[caissiel]

I get well over 200k miles on my vehicles and never idle any vehicles. Be at stops or before I take off. Been doing it for 45 years. An automatic transmission is different as its programer to shift at special times before heating up. It's very important to allow proper heating allowance before running hard. Remember that it takes less time to heat while applying proper power while driving then while idling. I could idle my truck for 1/2 hr and not get any hotter then driving 1/2 mile.

 

[FiremanBill]

My grandpappy told me that you should never start the vehicle and immediately take off!

He taught me to start the engine and let it run no less than 30 seconds before you take off.

I believe that this practice is why I generally get well over 100,000 miles on just about every vehicle I've ever owned without any major mechanical issues with them!

I watch people every day just jump in their cars and turn the key, and immediately take off!

And I know that a lot of them (people I know) seem to have their cars and trucks in the shop a lot . . .

Agreed John, I do the same, I always wait just a few seconds after starting anything up before yanking into gear and pulling out.

I am a runner, actually training for a 31 mile ultra marathon next month. I run just about every morning but I don't wake up, jump out of bed and run down the road either... The older I get the longer it takes me to be ready to go. lol

 

[porthole]

This is getting a bit off track with this comment, but, since I'm sure there is D'max owner or two viewing, warmup is a bit more critical when cold.
This is assuming the programming and mechanicals have not changed in the last several years.

The D'max Allison combo, as great as it is has one flaw. Transmission fluid flow when cold. High pressures with cold fluid is one of the reason the aluminum - rubber - aluminum trans hoses leak.
Those models can benefit with a short idle speed warmup.