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Discussion Starter · #1 ·
Hi all; sure hope I'm posting this in the right forum. Please LMK if I should move it elsewhere.

First, about the truck: It's a 2015 3500 LT w/ ~295k miles. It has an EFI tow tune and EGR delete (done by previous owner) and a lift pump (done by me), otherwise its stock. Spent its previous life (up to about 280k miles) as a show horse hauler in the Midwest, but now unfortunately has a blown head gasket.

I've ordered everything I need to replace the gaskets (inc. ARP studs) as well as a few wear items that I plan to replace while I'm at it (water pump, glow plugs).

So my question for the brain trust here: What other components would you replace while you're in there? I'm thinking along the lines of: turbo, injectors, fuel pump, etc..

I really don't care for more power; it's got more than enough pep for me, and I'm mainly looking for another 300k out of her if possible. I have an AD165 LP installed currently and run a lubricity additive, so IDK if I need to replace the CP4, but I'm open to suggestion there. As far as the injectors, I really don't know... Would it just be best practice to replace them with the engine out? Same with turbo. I'm assuming its gathered a bit of play in the components over time, but should I hold off, or be proactive and address it now?

That's really all that came to my mind, but I'm interested to hear what you all think. Thanks in advance!

EDIT: As soon as I hit "Post" another thought occurred: I'm debating ordering new heads vs. taking the existing to a shop. Thoughts on that are much appreciated as well. Thanks!
 

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If it were mine...if i'm in there i'd do the CP3 conversion. As you said it made it 280k on the CP4 but...if going to keep it that extra 300k at least...its a good piece of mind in my opinion. And they make no tune cp3 swap kits i've seen.

Turbo check and see if any visible chipping, feel for end play. Turbo is up top and replaceable in the truck if that ever went. Same with injectors. Have them bench tested and if they are good, run em.

Why are you pulling the engine for a HG though? I know its more accessible but overall more time i'd guess?
 

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2015 Duramax LTZ Z71
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If it were mine...if i'm in there i'd do the CP3 conversion. As you said it made it 280k on the CP4 but...if going to keep it that extra 300k at least...its a good piece of mind in my opinion. And they make no tune cp3 swap kits i've seen.

....
No tune and 50-state compliant CP3 kits

ssdiesel.com/product/lml-cp3-conversions/

industrialinjection.com/product/lml-duramax-cp4-to-cp3-conversion-kit-with-pump-factory-fit/

https://www.injectorsdirect.com/pro...version-kit-50-state-carb-compliant-with-dpf/

xtremediesel.com/industrial-injection-436401-cp4-to-cp3-conversion-kit-with-pump
 

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Discussion Starter · #4 ·
If it were mine...if i'm in there i'd do the CP3 conversion. As you said it made it 280k on the CP4 but...if going to keep it that extra 300k at least...its a good piece of mind in my opinion. And they make no tune cp3 swap kits i've seen.

Turbo check and see if any visible chipping, feel for end play. Turbo is up top and replaceable in the truck if that ever went. Same with injectors. Have them bench tested and if they are good, run em.

Why are you pulling the engine for a HG though? I know its more accessible but overall more time i'd guess?
Thanks for the suggestion! So, I think I will be going with the CP3 swap. And about pulling the engine: It's about to start getting cold where I live and unfortunately, my truck wont fit all the way in my garage, so I'm pulling the engine and putting it in my garage so I can work on it when I have time, regardless of the weather.
 

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I’d also do both main seals and reseal upper and lower oil pans (the LMLs like to leak). Doing the rear main seal requires removing the flywheel and them bolts are TY so get ARP flywheel bolts to replace. Also get a ARP balancer bolt. If you feel ambitious you could change all other seals and gaskets on the engine which is what i did when i had mine out for HGs.
 
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Discussion Starter · #7 ·
Thanks Dune my lack of punctuation wasnt clear. I mean there are existing 'no tune' kits available haha.
Thanks, Goat! After a little digging at xtremediesel, I think I'm going to go with this kit: Fleece FPE-LML-CP3-FF-3K LML CP3 Conversion Kit with CP3K Pump
I’d also do both main seals and reseal upper and lower oil pans (the LMLs like to leak). Doing the rear main seal requires removing the flywheel and them bolts are TY so get ARP flywheel bolts to replace. Also get a ARP balancer bolt. If you feel ambitious you could change all other seals and gaskets on the engine which is what i did when i had mine out for HGs.
Sorry what does "TY" mean? Is it like a stretch bolt that is one-time use or something?
 

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Yes. TY is short for torque to yield.
 
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You don't need to replace the damper or flywheel bolts. No one will argue if you do though.
Make sure to check each piston for cracking. That is the next item of concern after the good ole head gaskets. The OE piston is a $50 paperweight. (Cheap).
And since you will have the engine removed, replace your factory oil cooler with a 17-19 L5P oil cooler.

Sent from my SM-G960U1 using Tapatalk
 
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Discussion Starter · #11 ·
You don't need to replace the damper or flywheel bolts. No one will argue if you do though.
Make sure to check each piston for cracking. That is the next item of concern after the good ole head gaskets. The OE piston is a $50 paperweight. (Cheap).
And since you will have the engine removed, replace your factory oil cooler with a 17-19 L5P oil cooler.

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Hey, thanks for the response. So yeah, definitely going to take a close look at the pistons and cylinder walls. Didn't even have the oil cooler on my radar, looking into that now. Thanks again!
 

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If you are going for another 300,000 miles then you should look at this as restoring the engine to like new condition. While I had the pan off to reseal it I would surely plastigage the bearings. They will probably be good to go but now is the time to find out.


I'd strongly consider an new oil pump. It's $78 on Rock Auto. With the engine out it would be simple to replace. With the engine in it would be (explicative deleted) difficult.

Something to consider would be an additional block heater on the other side of the engine from the factory heater. Makes warming the engine much faster if that is a consideration.


I think head studs for a nearly stock engine are a waste of money. The latest head bolts are plenty good enough. If you are set on studs then have a look at this video:


I would have your stock heads checked carefully by a shop and keep them if they have no problems. The valves should be examined at the same time. It probably wouldn't need a valve job but now is the time to find out.

Plan on removing a lot of carbon from various places. This stuff works:


I'd have to be really strapped for cash not to replace the CP4 with a CP3 at this time. I don't think I would do injectors now though, unless they have problems. It isn't that difficult to do them later in the truck and they aren't cheap.

I would look at providing a bridge between the CP inlet to the fuel return line to the tank. This would allow fuel to circulate more freely. Your lift pump is capable of delivering about 7 times as much fuel as your engine can use under max power. Under normal power it is capable of about 30 times the fuel needed. What happens is that the lift pump develops pressure until it opens it's own internal relief valve. Most of the fuel just circulates around through the lift pump getting heated in the process. That isn't usually a good thing. Your truck comes from the factory with a fuel cooler for a good reason.

By providing a return line from the CP inlet you will be allowing the fuel to circulate through the filters several times. This makes the system fully self priming. When you change the filters or run out of fuel it will start right up again if you let the lift pump run for a few seconds first.

All of that circulation through the filters doesn't mean the fuel will be 30 times cleaner but it does mean it will be a little cleaner/dryer. The cost of this mod is a bit of hose, a couple of fittings, a check valve and a little brazing. Then the grossly oversized lift pump would at least be doing something other than heat the fuel. People often overlook the fact that the stock fuel setup uses vacuum to suck fuel from the tank to the CP. That means there can be no where for a lift pump to send excess fuel because if there were the CP would also draw from there without a lift pump.

Here are some ideas on what it would take:

check valve:
Amazon.com : 1/2" check valve A check valve takes a little pressure to open so having it in the bridge hose would not only prevent the CP from drawing from the unfiltered return line if the lift pump failed but it would also hold a small amount of pressure at the CP inlet, for what ever use that might be.

Hose:
https://www.amazon.com/ACDelco-32106-Professional-Bulk-Reel/dp/B0013FXWSI/ref=sr_1_3?crid=2F6VN2Y8JX6EO&dchild=1&keywords=1/2+fuel+hose+diesel&qid=1633589852&sprefix=1/2"+fuel+hose,aps,280&sr=8-3 You will only need a few inches but what the heck.

Hose barb fitting to braze onto CP inlet and return pipes:

1/2" Hose barb tee (if you don't want to mess with brazing):

When a bolt is torqued to yield a portion of the bolt stretches beyond it's elastic limit. That means it is permanently stretched. The result is a narrowing of the bolt where the stretch occurred. Some torque to yield bolts have a specification for how much that portion of the bolt can narrow before it is not useable. Another way to tell if a torque to yield bolt is still good is that a specification can be given for the minimum torque of the bolt. As the bolt stretches it becomes weaker. If it stretches too much it will be too weak to do the job and will never reach the specified torque. If it will reach the minimum specified torque then you can still use it. Mostly they don't trust us so they just say that the bolt isn't reusable. If you can see any narrowing of the bolt by using a straight edge against the side of the bolt then it is probably done for.

A torque to yield specification typically goes like this:

Install all bolts in the assembly finger tight. This ensures that all of the bolts will go in and that nothing is misaligned.
Torque each bolt in the assembly to some low figure. Typically something like 15-25 ft-lb. This ensures that the part is fully seated and ready to have pressure applied.
Torque each bolt to some high figure. This is typically 60-75 ft-lb. This sets the initial condition for torque to yield. All of the bolts are loaded fairly equally.
Turn each bolt a specific angle. This is typically 60, 90 or 180 degrees. This may be the end of the sequence. If it is you should feel the bolt yield near the end of the turn.
Turn each bolt an additional angle. This is typically the same as the previous angle but not always. You should definitely feel the bolt yield during this turn.

The feel of a yield is that there will be more and more resistance until a certain point. At that point the resistance will stop increasing and may even drop off a little.

Torque to yield produces more consistent results than a non-yielding torqueing. Not to be confused with non-yielding twerking.
 

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Hey mizterwizard i have yet to see a LML with a fuel cooler.
 

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Discussion Starter · #15 ·
If you are going for another 300,000 miles then you should look at this as restoring the engine to like new condition. While I had the pan off to reseal it I would surely plastigage the bearings. They will probably be good to go but now is the time to find out.


I'd strongly consider an new oil pump. It's $78 on Rock Auto. With the engine out it would be simple to replace. With the engine in it would be (explicative deleted) difficult.

Something to consider would be an additional block heater on the other side of the engine from the factory heater. Makes warming the engine much faster if that is a consideration.


I think head studs for a nearly stock engine are a waste of money. The latest head bolts are plenty good enough. If you are set on studs then have a look at this video:


I would have your stock heads checked carefully by a shop and keep them if they have no problems. The valves should be examined at the same time. It probably wouldn't need a valve job but now is the time to find out.

Plan on removing a lot of carbon from various places. This stuff works:


I'd have to be really strapped for cash not to replace the CP4 with a CP3 at this time. I don't think I would do injectors now though, unless they have problems. It isn't that difficult to do them later in the truck and they aren't cheap.

I would look at providing a bridge between the CP inlet to the fuel return line to the tank. This would allow fuel to circulate more freely. Your lift pump is capable of delivering about 7 times as much fuel as your engine can use under max power. Under normal power it is capable of about 30 times the fuel needed. What happens is that the lift pump develops pressure until it opens it's own internal relief valve. Most of the fuel just circulates around through the lift pump getting heated in the process. That isn't usually a good thing. Your truck comes from the factory with a fuel cooler for a good reason.

By providing a return line from the CP inlet you will be allowing the fuel to circulate through the filters several times. This makes the system fully self priming. When you change the filters or run out of fuel it will start right up again if you let the lift pump run for a few seconds first.

All of that circulation through the filters doesn't mean the fuel will be 30 times cleaner but it does mean it will be a little cleaner/dryer. The cost of this mod is a bit of hose, a couple of fittings, a check valve and a little brazing. Then the grossly oversized lift pump would at least be doing something other than heat the fuel. People often overlook the fact that the stock fuel setup uses vacuum to suck fuel from the tank to the CP. That means there can be no where for a lift pump to send excess fuel because if there were the CP would also draw from there without a lift pump.

Here are some ideas on what it would take:

check valve:
Amazon.com : 1/2" check valve A check valve takes a little pressure to open so having it in the bridge hose would not only prevent the CP from drawing from the unfiltered return line if the lift pump failed but it would also hold a small amount of pressure at the CP inlet, for what ever use that might be.

Hose:
https://www.amazon.com/ACDelco-32106-Professional-Bulk-Reel/dp/B0013FXWSI/ref=sr_1_3?crid=2F6VN2Y8JX6EO&dchild=1&keywords=1/2+fuel+hose+diesel&qid=1633589852&sprefix=1/2"+fuel+hose,aps,280&sr=8-3 You will only need a few inches but what the heck.

Hose barb fitting to braze onto CP inlet and return pipes:

1/2" Hose barb tee (if you don't want to mess with brazing):

When a bolt is torqued to yield a portion of the bolt stretches beyond it's elastic limit. That means it is permanently stretched. The result is a narrowing of the bolt where the stretch occurred. Some torque to yield bolts have a specification for how much that portion of the bolt can narrow before it is not useable. Another way to tell if a torque to yield bolt is still good is that a specification can be given for the minimum torque of the bolt. As the bolt stretches it becomes weaker. If it stretches too much it will be too weak to do the job and will never reach the specified torque. If it will reach the minimum specified torque then you can still use it. Mostly they don't trust us so they just say that the bolt isn't reusable. If you can see any narrowing of the bolt by using a straight edge against the side of the bolt then it is probably done for.

A torque to yield specification typically goes like this:

Install all bolts in the assembly finger tight. This ensures that all of the bolts will go in and that nothing is misaligned.
Torque each bolt in the assembly to some low figure. Typically something like 15-25 ft-lb. This ensures that the part is fully seated and ready to have pressure applied.
Torque each bolt to some high figure. This is typically 60-75 ft-lb. This sets the initial condition for torque to yield. All of the bolts are loaded fairly equally.
Turn each bolt a specific angle. This is typically 60, 90 or 180 degrees. This may be the end of the sequence. If it is you should feel the bolt yield near the end of the turn.
Turn each bolt an additional angle. This is typically the same as the previous angle but not always. You should definitely feel the bolt yield during this turn.

The feel of a yield is that there will be more and more resistance until a certain point. At that point the resistance will stop increasing and may even drop off a little.

Torque to yield produces more consistent results than a non-yielding torqueing. Not to be confused with non-yielding twerking.
Awesome amount of info, thank you! I went ahead and picked up the oil pump as suggested. Seems like a no-brainer considering the price and current level of access with the motor out. Luckily I have access to a bore gauge which I will be using to test clearances. And I use Hoppes for my guns anyway, so I happen to have a good amount of that on-hand for carbon removal.

I decided to go with slightly higher-flowing injectors (S&S TorqueMasters), and if the turbo ever gives me problems, I'll replace it with one with a bit more power ceiling, so I did go ahead and opt for studs. Wish I would have seen the video you linked before purchase, but I got an incredible deal on the ARPs, so I'm not going to complain too much. Also it looks like as of about a month ago, the IFG studs are no longer available. Either way, that extra clamp I'll get will put my mind at ease if I ever do want to chase extra power.

Thanks again for all the info!
 

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Lot of good suggestions here so I won't re-hash any of it except for the pistons. If I were tearing apart a 300k mile LML and shooting for another 300k, I'd drop a set of Mahle pistons in it. I wouldn't even mess with inspecting for cracks. The stockers are weak at best, I'll just leave it at that. Many have cracked even at stock HP. They won't take towing with power mods, not for long anyway.
 

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Discussion Starter · #17 ·
Lot of good suggestions here so I won't re-hash any of it except for the pistons. If I were tearing apart a 300k mile LML and shooting for another 300k, I'd drop a set of Mahle pistons in it. I wouldn't even mess with inspecting for cracks. The stockers are weak at best, I'll just leave it at that. Many have cracked even at stock HP. They won't take towing with power mods, not for long anyway.
Very good point...

Ugh, this is getting more and more expensive! Thanks for the suggestion though!
 

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Very good point...

Ugh, this is getting more and more expensive! Thanks for the suggestion though!
Ahh, cheer up. You think the LML is painful? I just went through a 6.0 Ford. I never officially added up all the receipts, but I have a pretty good idea. And I'm too ashamed to even publish the number!

You'll have a good solid motor when you're done.
 

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Discussion Starter · #20 ·
Ahh, cheer up. You think the LML is painful? I just went through a 6.0 Ford. I never officially added up all the receipts, but I have a pretty good idea. And I'm too ashamed to even publish the number!

You'll have a good solid motor when you're done.
I actually just sold my 6.0 off about a year ago because I didn't want to go to all the trouble of bulletproofing it. And now here I am... :ROFLMAO:😭
 
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