Alright everyone, i think the time has come to make a single thread to cover everything 6.4 Powerstroke. This will cover all the basic and commonly asked questions, diagnostics, maintenance, and tips to get the new 6.4 owners up to speed on what its like to own one of these trucks and maybe even get veteran members to learn a thing or two as well 
I have gone somewhat in depth and because of that i will have three posts to fit it all in. Although i tried to keep everything as relative and as accurate as possible, i am not perfect. That being said, if you see anything wrong or should be added please comment and i will add/change if it is a good fit. Also realize (especially in the modification chapter) that I can’t cover every aspect of every item. This is just to point you, the reader, in the right direction. Admins if you think this is a good thread please add it as a sticky so all the new guys and visitors can find it easily. Lets get right into it!
Chapters:
Chapter 1: Intro
Chapter 2: Caring for your 6.4/ driving habits
Chapter 3: “Bulletproofing” fixing the time bombs
Chapter 4: General performance modifications
Chapter 5: Common problems and how to fix them
Chapter 6: Buying a 6.4 and what to look for
Summary:
Chapter 1: Introduction to the 6.4
In response to the plagued 6.0 Powerstroke engine, Ford once again called on Navistar to build a new engine to address the previous issues and even improve on the old design to stay on top of the market. Navistar answered the call with the 6.4l Powerstroke engine.
With the company promising the new power plant to be one of the best and most resilient to hit the market , Ford put the new engine into the second generation body style of Super Duty trucks. On December 18th 2006, the first 6.4l Powerstroke was produced.
The new engine was a 390.5 cubic inch v8, featuring sequential variable geometry turbos, piezo injectors, and a high pressure fuel pump (hpfp) capable of producing in excess of 30,000 psi of pressure. It was one of the strongest engines in its class producing 350 horsepower and 650 foot pounds of torque at the crank. It also was the first diesel engine ford sold that featured a full emissions system, including dual exhaust gas recirculation (egr) coolers, catalytic converter (cat), and a diesel particulate filter (dpf).
With Ford promoting the new trucks as the answer every ford fan was waiting for, it was a big initial success, however it was short lived. After seasons started passing, the quality of Navistar started to rear its head once again....
With flashbacks of the 6.0 Powerstroke engine on the minds of Ford and the market showing the dissatisfaction toward the blue oval, Ford decided to sell the final 6.4l engine equipped Super Duty by March of 2010.
Even though many 6.4’s have been in the shops one time or another, the engine still continues to prove that even though it has demons, they are soon woo’ed by the excellent responsiveness and drivability it has to offer. And the aftermarket community has dawned a soft side for the 6.4 due to the fact that it can make the most power of any light vehicle diesel engine to this day with simple bolt-ons, surpassing 1200 foot pound of torque with ecu tuning alone.
The 6.4l Powerstroke engine certainly isn’t the best diesel ever made, but it does reward those who don’t give up on it with excellent drivability and power.
Chapter 2: Caring for your 6.4/driving habits
*Everything covered in this chapter is said having the stock 6.4 powerplant in mind. Information may vary if your engine has aftermarket modifications and/or parts.
Your 6.4 is an amazing tool which is always there when you need it. Whether you are in -20 degree weather offroading to get to your cabin, towing 20,000 pounds worth of backhoe, or simply taking your significant other out to dinner, your 6.4 can do some amazing things. But those things don’t come free. The 6.4 Powerstroke is one of, if not the most picky engine when it comes to maintainence and driving habits
-Maintenance
If you do not keep up on the maintenance you will have problems.
Lets start with simple maintenance etiquette. Consider your owner’s manual the holy book, it is how you live when dealing with your truck. When in doubt refer to your manual! It has your maintenance schedule, fuse diagrams, and everything else important to know and keep your 6.4 working well.
Speaking of maintainence intervals, your manual has normal duty and severe duty schedules. It is a good idea to default to the severe schedule due to the 6.4 engine problems (which is covered in the next chapter). The severe schedule recommends changing the oil and filter at 5,000 miles and fuel filters at 15,000 miles. Do these things on time with oem Motorcraft brand filters and you will be one step ahead of the rest on fighting future problems.
When changing your oil, the default is Motorcraft brand oil with the weight and viscosity your manual recommends. You can put different brands of oil in your 6.4 but be sure it is a well trusted and proven brand and it be at least a synthetic blend, no conventional oil is allowed. When changing the oil remove the filter first. This will make any loose foreign material not captured fall into the oil that will later be drained. Replace the filter with a oem filter with o ring and then fill with new oil which is 15 quarts with filter unless otherwise stated.
Fuel filters are next and just as important. These are your first and last line of defense before the fuel gets to the hpfp. The hpfp is complex and advanced part that needs extremely tight tolerances in order to work properly. Any foreign material can compromise the pump and cause it to fail, costing thousands to repair. That is why the fuel filters are so important to stay on top of. There are two filters, one located on the fuel conditioning unit mounted to the frame rail under the cab and the other in the engine bay located next to the oil filter. Start by draining the water separator by opening the valve on the fuel conditioning unit until water is purged and diesel starts to come out. Close the valve and remove the frame rail filter and replace with an oem filter and o ring. Next remove the engine fuel filter and replace the filter with a new oem as well. Now this is an important step, you need to purge the air from the fuel system BEFORE attempting to start. To purge the system, turn the key to acc (notch before starting) and keep it there for 30 seconds. Once the 30 seconds has passed, return the key to off for 3 seconds. Repeat a total of 6 times. Once you have completed the step, attempt to start the engine. If starts then dies, repurge 3 times instead of 10 and then attempt to start. It isn’t uncommon for it to stall once so don’t worry.
Oil and fuel are the most important in terms of maintenance, if you are going to neglect on certain maintenance items please do not do it with the fuel or oil filters. Those protect the lifeblood of these engines and if you don’t give them the attention they deserve your engine will suffer. I cannot stress that enough!
The most simple will probably be the air filter. It is only recommended to change the filter when the air filter minder throws a check engine light. It will come on when the restriction in the air intake becomes too great. When changing the filter you will get the most filtration out of an oem. If you want a little more flow, AFE makes a drop-in filter that will do the trick. AFE is the only stock airbox aftermarket filter I can recommend for the 6.4’s. Other brands either don’t provide enough flow or filtration to do the job adequately.
Next is coolant. Gold Motorcraft coolant is the go to for 6.4. Some 6.4 owners use Caterpillar brand extended life coolant (ELC) instead of Motorcraft which is acceptable to do. Always keep your coolant between the cold fill lines and change the coolant at 100,000 miles, simple enough.The coolant capacity is 29.6 quarts which includes the heater core and coolant recovery tank. Don’t forget to check your fuel coolant reservoir regularly as well. It is the small black steel tank to the left of the power steering, it uses the same coolant and is completely independent of the main coolant system. So if you drain one for new coolant don’t forget to drain the other. There is a lengthy procedure to purge the coolant system and refill to prevent cavitation. You can find that procedure online. And to end the coolant paragraph, it is a good idea to replace the thermostats and coolant pressure cap when replacing the coolant as those items have a limited life before they they become a liability.
Transmissions have a hard life. They take the tremendous amount of torque diesels make and harness it for efficient use. To do the demanding job they need a good oil that can not only lubricate it but cool it as well. If you have a 5r100 (auto) you should replace the fluid at 60,000 miles and if you have a ZF S6-750 (manual) you can go between 70,000 and 100,000 miles depending on your driving characteristics. When changing the automatic transmission fluid, most 6.4 owners drop the oil pan and replace the fluid that was removed rather than doing a “heated flush service”. *This is due to the belief that the heated service puts excess pressure and stress on the system when purging all the old oil out of the transmission, however there is limited evidence on this matter to say conclusively. If you decide to change the fluid yourself, use Mercon Lv (previously sp) and replace whatever you took out of the system. If you decide to do a heated service or another way that completely drains the transmission, the quantity is 17.5 quarts with the filter change. Dont forget to change the transmission filter as well. Depending on the year your truck was built you either have an external filter for early years or an internal filter for later years.
*For the ZF manual transmission is simple. Just drain and replace with 5.8 quarts of Mercon V. You should fill until the fluid reaches the top fill hole. You will need a pump to get the fluid into the manual transmission
Transfer cases are simple. There is a fill and drain bolt on the rear side of the case. Remove both and drain the old fluid, replace the drain plug with new teflon tape, and fill the case to the oil fill hole which should be about two quarts. Once filled replace the fill plug with new teflon tape. The fluid called for is Motorcraft transfer case fluid (xl-12). Be aware, you will need a pump to get the fluid into the case due to limited access.
The last maintainence items are the differentials. For the sterling 10.5 (srw) axles they are quoted as a “sealed” unit meaning that the fluid does not need to be changed for the life of the vehicle. However it is common practice to change the fluid at 100,000 miles. The front differential is 2.8 liters of 80w-90 on all Super Duty’s and the rear is 3.3 liters of 75w-140. For the dana (drw) axles it is recommended to change at 50,000 miles and it is not a sealed unit. The oil for the Dana m80 is 4 liters of 75w-90 and the Dana s110/130 likes 6.6 liters of 75w-140.
One more thing i want to touch on even though its not necessary is fuel additives. Contrary to popular believe, you don’t need to be in below freezing temps to have a reason to run them nowadays. Ford actually recommends running their brand of Motorcraft additive in every tank of diesel to boost the lubrication numbers. Since modern diesel is ultra low sulfur and doesn’t possess the lubrication that it used to in older diesel fuel it is smart to run them, especially since 6.4’s have a hpfp. It could save you thousands down the road. The most popular brand is Opti-lube which provides a full line of additives so you can pick the one thats right for you. Other good brands to look at are Rev-x and Archoil. Whatever you choose is better than running nothing at all, some even run pure two-stroke oil although i cant personally condone using it. Also it is good practice to fill up at stations that go through a decent amount of fuel, that way there is limited condensation in the fuel and it limits the chances of water contamination.
⁃ Daily driving habits
Even though diesel engines are famous for being able to take abuse and pass a million miles doing it, the 6.4 isn’t one of them. It is a somewhat fragile engine when compared to similar diesel engines due to the last minute nature of the design coupled with band aid fixes to pass emissions before being sold. With that being said, following these daily driving tips will minimize wear and tear and keep your 6.4 happy.
When starting up your 6.4 from cold always let the glow plug light turn off before starting. This will make the engine start quicker and get oil flowing faster to the nozzles reducing start up wear. Even a couple extra seconds after wouldn’t hurt. *Once started, don’t start driving immediately. Give the engine 15 or so seconds to get the fluids moving, oil to the surfaces that need it, and pistons heated up. After that and you start moving, don’t mash the gas. You should let it get up to operating temperature or at least 150 degrees oil temperature before asking for significant power or high rpm.
When your 6.4 is all warmed up and you are driving always remember it is a truck, not a racecar. If you want to go fast and race, buy a mustang or have alot of cash on standby because 6.4’s cant handle continuous abuse. They need to be driven practically and efficiently. *If you don’t heed this warning you will kill your engine sooner than later.
From the factory your 6.4 is equipped with a diesel particulate filter (dpf). The filter captures diesel soot that is later burned off by either passive or active regeneration. Passive regeneration is done while you drive normally. When passive regeneration isn’t enough, active regeneration is activated to clean the filter. It is activated when the back pressure threshold is exceeded. When that happens, a message will appear on your dash screen stating “drive to clean exhaust filter”. After the message is stated you need to drive your 6.4 above 30 miles an hour to initiate the cleaning. The productivity screen will notify you when the cleaning is completed. The less you stop, the more fuel, the quicker it cleans, and you save some wear and tear on your engine.
Whenever you are carrying/towing a load, tow haul is recommended. Placing your 6.4 into tow haul will stop it from “hunting’ for the right gear, keep it in the torque band longer, and cut down on shifts reducing fluid temperature and clutch wear. It will also allow you to take advantage of engine braking when slowing down. While you are engine braking turning on your a/c will further increase the total engine braking provided, even though it won’t be a significant increase. If you are in tow haul and are taking advantage of engine braking, it will also help cool down your engine. This is due to the fact that no fuel is being burned and the engine is only circulating non heated air, transporting heat out of the engine. This is the most critical time if you wish to lower engine temperature as no other method cools the engine as quickly or efficiently.
Long or frequent idling is not condoned in 6.4 engines as it could lead to increased carbon and soot buildup down the road. To determine if your 6.4 has a lot of idle time, divide the total miles by the engine hours. Anything over 35 is considered high idling and you have an increased risk of carbon/soot related problems.
Driving your 6.4 with the a/c or defroster on increases load on the engine, this in turn increases engine temperature, fuel consumption, and power loss. If you don’t need the systems on go ahead and shut them off. When towing a heavy load uphill this is also a good time to shut them down to help keep engine temperatures in check.
After you are done driving you 6.4 it is recommended you let you it idle before shutting down, this gives the turbos a chance to cool down. Not cooling down the turbos after extended driving or moving heavy loads could cause turbo problems down the road. Cool down time varies depending on your circumstances but the manual recommends 3-5 minutes for heavy loads, high ambient temperature, or high rpm.
If you are driving a manual transmission, a good skill to learn is rev matching. Rev matching is a downshifting technique in which you shift out of one gear, tap the gas to bring the rpms up, and shift into the lower gear and release the clutch. If you do it right you will have a smooth transition from one gear to the other increasing clutch life and providing a smoother driving experience.
I have gone somewhat in depth and because of that i will have three posts to fit it all in. Although i tried to keep everything as relative and as accurate as possible, i am not perfect. That being said, if you see anything wrong or should be added please comment and i will add/change if it is a good fit. Also realize (especially in the modification chapter) that I can’t cover every aspect of every item. This is just to point you, the reader, in the right direction. Admins if you think this is a good thread please add it as a sticky so all the new guys and visitors can find it easily. Lets get right into it! Chapters:
Chapter 1: Intro
Chapter 2: Caring for your 6.4/ driving habits
Chapter 3: “Bulletproofing” fixing the time bombs
Chapter 4: General performance modifications
Chapter 5: Common problems and how to fix them
Chapter 6: Buying a 6.4 and what to look for
Summary:
Chapter 1: Introduction to the 6.4
In response to the plagued 6.0 Powerstroke engine, Ford once again called on Navistar to build a new engine to address the previous issues and even improve on the old design to stay on top of the market. Navistar answered the call with the 6.4l Powerstroke engine.
With the company promising the new power plant to be one of the best and most resilient to hit the market , Ford put the new engine into the second generation body style of Super Duty trucks. On December 18th 2006, the first 6.4l Powerstroke was produced.
The new engine was a 390.5 cubic inch v8, featuring sequential variable geometry turbos, piezo injectors, and a high pressure fuel pump (hpfp) capable of producing in excess of 30,000 psi of pressure. It was one of the strongest engines in its class producing 350 horsepower and 650 foot pounds of torque at the crank. It also was the first diesel engine ford sold that featured a full emissions system, including dual exhaust gas recirculation (egr) coolers, catalytic converter (cat), and a diesel particulate filter (dpf).
With Ford promoting the new trucks as the answer every ford fan was waiting for, it was a big initial success, however it was short lived. After seasons started passing, the quality of Navistar started to rear its head once again....
With flashbacks of the 6.0 Powerstroke engine on the minds of Ford and the market showing the dissatisfaction toward the blue oval, Ford decided to sell the final 6.4l engine equipped Super Duty by March of 2010.
Even though many 6.4’s have been in the shops one time or another, the engine still continues to prove that even though it has demons, they are soon woo’ed by the excellent responsiveness and drivability it has to offer. And the aftermarket community has dawned a soft side for the 6.4 due to the fact that it can make the most power of any light vehicle diesel engine to this day with simple bolt-ons, surpassing 1200 foot pound of torque with ecu tuning alone.
The 6.4l Powerstroke engine certainly isn’t the best diesel ever made, but it does reward those who don’t give up on it with excellent drivability and power.
Chapter 2: Caring for your 6.4/driving habits
*Everything covered in this chapter is said having the stock 6.4 powerplant in mind. Information may vary if your engine has aftermarket modifications and/or parts.
Your 6.4 is an amazing tool which is always there when you need it. Whether you are in -20 degree weather offroading to get to your cabin, towing 20,000 pounds worth of backhoe, or simply taking your significant other out to dinner, your 6.4 can do some amazing things. But those things don’t come free. The 6.4 Powerstroke is one of, if not the most picky engine when it comes to maintainence and driving habits
-Maintenance
If you do not keep up on the maintenance you will have problems.
Lets start with simple maintenance etiquette. Consider your owner’s manual the holy book, it is how you live when dealing with your truck. When in doubt refer to your manual! It has your maintenance schedule, fuse diagrams, and everything else important to know and keep your 6.4 working well.
Speaking of maintainence intervals, your manual has normal duty and severe duty schedules. It is a good idea to default to the severe schedule due to the 6.4 engine problems (which is covered in the next chapter). The severe schedule recommends changing the oil and filter at 5,000 miles and fuel filters at 15,000 miles. Do these things on time with oem Motorcraft brand filters and you will be one step ahead of the rest on fighting future problems.
When changing your oil, the default is Motorcraft brand oil with the weight and viscosity your manual recommends. You can put different brands of oil in your 6.4 but be sure it is a well trusted and proven brand and it be at least a synthetic blend, no conventional oil is allowed. When changing the oil remove the filter first. This will make any loose foreign material not captured fall into the oil that will later be drained. Replace the filter with a oem filter with o ring and then fill with new oil which is 15 quarts with filter unless otherwise stated.
Fuel filters are next and just as important. These are your first and last line of defense before the fuel gets to the hpfp. The hpfp is complex and advanced part that needs extremely tight tolerances in order to work properly. Any foreign material can compromise the pump and cause it to fail, costing thousands to repair. That is why the fuel filters are so important to stay on top of. There are two filters, one located on the fuel conditioning unit mounted to the frame rail under the cab and the other in the engine bay located next to the oil filter. Start by draining the water separator by opening the valve on the fuel conditioning unit until water is purged and diesel starts to come out. Close the valve and remove the frame rail filter and replace with an oem filter and o ring. Next remove the engine fuel filter and replace the filter with a new oem as well. Now this is an important step, you need to purge the air from the fuel system BEFORE attempting to start. To purge the system, turn the key to acc (notch before starting) and keep it there for 30 seconds. Once the 30 seconds has passed, return the key to off for 3 seconds. Repeat a total of 6 times. Once you have completed the step, attempt to start the engine. If starts then dies, repurge 3 times instead of 10 and then attempt to start. It isn’t uncommon for it to stall once so don’t worry.
Oil and fuel are the most important in terms of maintenance, if you are going to neglect on certain maintenance items please do not do it with the fuel or oil filters. Those protect the lifeblood of these engines and if you don’t give them the attention they deserve your engine will suffer. I cannot stress that enough!
The most simple will probably be the air filter. It is only recommended to change the filter when the air filter minder throws a check engine light. It will come on when the restriction in the air intake becomes too great. When changing the filter you will get the most filtration out of an oem. If you want a little more flow, AFE makes a drop-in filter that will do the trick. AFE is the only stock airbox aftermarket filter I can recommend for the 6.4’s. Other brands either don’t provide enough flow or filtration to do the job adequately.
Next is coolant. Gold Motorcraft coolant is the go to for 6.4. Some 6.4 owners use Caterpillar brand extended life coolant (ELC) instead of Motorcraft which is acceptable to do. Always keep your coolant between the cold fill lines and change the coolant at 100,000 miles, simple enough.The coolant capacity is 29.6 quarts which includes the heater core and coolant recovery tank. Don’t forget to check your fuel coolant reservoir regularly as well. It is the small black steel tank to the left of the power steering, it uses the same coolant and is completely independent of the main coolant system. So if you drain one for new coolant don’t forget to drain the other. There is a lengthy procedure to purge the coolant system and refill to prevent cavitation. You can find that procedure online. And to end the coolant paragraph, it is a good idea to replace the thermostats and coolant pressure cap when replacing the coolant as those items have a limited life before they they become a liability.
Transmissions have a hard life. They take the tremendous amount of torque diesels make and harness it for efficient use. To do the demanding job they need a good oil that can not only lubricate it but cool it as well. If you have a 5r100 (auto) you should replace the fluid at 60,000 miles and if you have a ZF S6-750 (manual) you can go between 70,000 and 100,000 miles depending on your driving characteristics. When changing the automatic transmission fluid, most 6.4 owners drop the oil pan and replace the fluid that was removed rather than doing a “heated flush service”. *This is due to the belief that the heated service puts excess pressure and stress on the system when purging all the old oil out of the transmission, however there is limited evidence on this matter to say conclusively. If you decide to change the fluid yourself, use Mercon Lv (previously sp) and replace whatever you took out of the system. If you decide to do a heated service or another way that completely drains the transmission, the quantity is 17.5 quarts with the filter change. Dont forget to change the transmission filter as well. Depending on the year your truck was built you either have an external filter for early years or an internal filter for later years.
*For the ZF manual transmission is simple. Just drain and replace with 5.8 quarts of Mercon V. You should fill until the fluid reaches the top fill hole. You will need a pump to get the fluid into the manual transmission
Transfer cases are simple. There is a fill and drain bolt on the rear side of the case. Remove both and drain the old fluid, replace the drain plug with new teflon tape, and fill the case to the oil fill hole which should be about two quarts. Once filled replace the fill plug with new teflon tape. The fluid called for is Motorcraft transfer case fluid (xl-12). Be aware, you will need a pump to get the fluid into the case due to limited access.
The last maintainence items are the differentials. For the sterling 10.5 (srw) axles they are quoted as a “sealed” unit meaning that the fluid does not need to be changed for the life of the vehicle. However it is common practice to change the fluid at 100,000 miles. The front differential is 2.8 liters of 80w-90 on all Super Duty’s and the rear is 3.3 liters of 75w-140. For the dana (drw) axles it is recommended to change at 50,000 miles and it is not a sealed unit. The oil for the Dana m80 is 4 liters of 75w-90 and the Dana s110/130 likes 6.6 liters of 75w-140.
One more thing i want to touch on even though its not necessary is fuel additives. Contrary to popular believe, you don’t need to be in below freezing temps to have a reason to run them nowadays. Ford actually recommends running their brand of Motorcraft additive in every tank of diesel to boost the lubrication numbers. Since modern diesel is ultra low sulfur and doesn’t possess the lubrication that it used to in older diesel fuel it is smart to run them, especially since 6.4’s have a hpfp. It could save you thousands down the road. The most popular brand is Opti-lube which provides a full line of additives so you can pick the one thats right for you. Other good brands to look at are Rev-x and Archoil. Whatever you choose is better than running nothing at all, some even run pure two-stroke oil although i cant personally condone using it. Also it is good practice to fill up at stations that go through a decent amount of fuel, that way there is limited condensation in the fuel and it limits the chances of water contamination.
⁃ Daily driving habits
Even though diesel engines are famous for being able to take abuse and pass a million miles doing it, the 6.4 isn’t one of them. It is a somewhat fragile engine when compared to similar diesel engines due to the last minute nature of the design coupled with band aid fixes to pass emissions before being sold. With that being said, following these daily driving tips will minimize wear and tear and keep your 6.4 happy.
When starting up your 6.4 from cold always let the glow plug light turn off before starting. This will make the engine start quicker and get oil flowing faster to the nozzles reducing start up wear. Even a couple extra seconds after wouldn’t hurt. *Once started, don’t start driving immediately. Give the engine 15 or so seconds to get the fluids moving, oil to the surfaces that need it, and pistons heated up. After that and you start moving, don’t mash the gas. You should let it get up to operating temperature or at least 150 degrees oil temperature before asking for significant power or high rpm.
When your 6.4 is all warmed up and you are driving always remember it is a truck, not a racecar. If you want to go fast and race, buy a mustang or have alot of cash on standby because 6.4’s cant handle continuous abuse. They need to be driven practically and efficiently. *If you don’t heed this warning you will kill your engine sooner than later.
From the factory your 6.4 is equipped with a diesel particulate filter (dpf). The filter captures diesel soot that is later burned off by either passive or active regeneration. Passive regeneration is done while you drive normally. When passive regeneration isn’t enough, active regeneration is activated to clean the filter. It is activated when the back pressure threshold is exceeded. When that happens, a message will appear on your dash screen stating “drive to clean exhaust filter”. After the message is stated you need to drive your 6.4 above 30 miles an hour to initiate the cleaning. The productivity screen will notify you when the cleaning is completed. The less you stop, the more fuel, the quicker it cleans, and you save some wear and tear on your engine.
Whenever you are carrying/towing a load, tow haul is recommended. Placing your 6.4 into tow haul will stop it from “hunting’ for the right gear, keep it in the torque band longer, and cut down on shifts reducing fluid temperature and clutch wear. It will also allow you to take advantage of engine braking when slowing down. While you are engine braking turning on your a/c will further increase the total engine braking provided, even though it won’t be a significant increase. If you are in tow haul and are taking advantage of engine braking, it will also help cool down your engine. This is due to the fact that no fuel is being burned and the engine is only circulating non heated air, transporting heat out of the engine. This is the most critical time if you wish to lower engine temperature as no other method cools the engine as quickly or efficiently.
Long or frequent idling is not condoned in 6.4 engines as it could lead to increased carbon and soot buildup down the road. To determine if your 6.4 has a lot of idle time, divide the total miles by the engine hours. Anything over 35 is considered high idling and you have an increased risk of carbon/soot related problems.
Driving your 6.4 with the a/c or defroster on increases load on the engine, this in turn increases engine temperature, fuel consumption, and power loss. If you don’t need the systems on go ahead and shut them off. When towing a heavy load uphill this is also a good time to shut them down to help keep engine temperatures in check.
After you are done driving you 6.4 it is recommended you let you it idle before shutting down, this gives the turbos a chance to cool down. Not cooling down the turbos after extended driving or moving heavy loads could cause turbo problems down the road. Cool down time varies depending on your circumstances but the manual recommends 3-5 minutes for heavy loads, high ambient temperature, or high rpm.
If you are driving a manual transmission, a good skill to learn is rev matching. Rev matching is a downshifting technique in which you shift out of one gear, tap the gas to bring the rpms up, and shift into the lower gear and release the clutch. If you do it right you will have a smooth transition from one gear to the other increasing clutch life and providing a smoother driving experience.
