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Hi all! New member here. I have a 2015 with 415k on it. I’ve had super luck with the truck overall, but alas I figured it had a blown head gasket when I was putting a gallon of coolant in at every fuel stop…
I found a diesel performance shop where I live in Ocala, FL. As I suspected they told me the head gasket was blown. Compression test was good, one cylinder was a little low but they suspected that was due to the head gasket.
I told them I wanted ARP head studs, due to the high mileage they would have thy head machined, etc. On my quote for the head gasket was also: engine water pump, thermostat (there was 2 different ones listed on quote?), and glow plugs.
He asked me about a few things:
1. Replacing all injectors. Injectors have never been replaced, so he recommended I replace all 8. I asked about doing a slightly bigger injector (30%) vs stock. They chose the S&S Diesel 30% injectors or just replace with Bosch reman injectors.
2. converting the CP4 to a CP3. Good idea? My dad has a Ram with the failed CP4, so I assume yes and I know if the CP4 fails that is a whole new fuel system… $$$$$
They chose the Fleece Performance conversion kit. Is this a good idea because I have over 400k even with my FASS?

While they have the truck, they are also doing the AC Actuator, as I have lived in Florida with virtually no AC on the drivers side for 2 years…

Some background, the truck was deleted and tuned around 150k, with a FASS, EFI Live. Transmission is stock. First major problem with the truck was around 230k when my alternator blew up and shredded the serpentine belt. Other than that, the truck has been wonderful and I hope to get many more miles out of it. I transport horses for a living, so most of my miles are highway miles.

Anything else I should consider getting done? This is a beautiful truck and looks immaculate and drives fantastic, especially considering the miles.
 

· Former GM Tech and parts
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I would say yes on the water pump and thermostats, and there are two thermostats in the Duramax engines, glow plugs are a good idea too since they will be out for getting the heads machined anyway. For the injectors, thats kinda up to you on- if they are working fine and you don't have any problems, I don't see any reason to spend the money on them. BUT, on the other hand, they will be out so its prime time to replace them. Other than T&D, do you have any other mods done to the truck? Because if not, I don't see any need to go oversized with injectors. I would recommend doing the cp3 conversion. My cp3 conversion kit came from Fleece and worked great, I already had a cp3 to put in so I didn't get the kit with cp3.
 

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Discussion Starter · #3 ·
I would say yes on the water pump and thermostats, and there are two thermostats in the Duramax engines, glow plugs are a good idea too since they will be out for getting the heads machined anyway. For the injectors, thats kinda up to you on- if they are working fine and you don't have any problems, I don't see any reason to spend the money on them. BUT, on the other hand, they will be out so its prime time to replace them. Other than T&D, do you have any other mods done to the truck? Because if not, I don't see any need to go oversized with injectors. I would recommend doing the cp3 conversion. My cp3 conversion kit came from Fleece and worked great, I already had a cp3 to put in so I didn't get the kit with cp3.

No other mods done to truck. I don’t want to put too much stress on the trans either. Injectors have been working fine but I’m not sure is that’s a part that fails often. Does the FASS help with the integrity of the injectors?
 

· Former GM Tech and parts
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The fass helps, both by pushing the fuel up to the cp4 as well as the added filtration. If there are no other mods, I definitely would not recommend oversized injectors- stock size is all you will need
 

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2015 Duramax LTZ Z71
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Wow - 415,000on a CP4. Must be something to having a FASS... Original injectors, etc. Super luck is an understatement.

Do you run any fuel additive?
 

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2011 GMC Sierra 2500 HD
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136 Posts
I don’t k ow what your budget is… my philosophy is replace all wear items you can afford and that are reasonable to replace . Example, thermostats, injectors, water pump, cp3 conversion FTW, etc. you don’t want to finish up all that work and have an injector go out and spend another 1500 or so to replace one when you could have done them all for a little more, or have a water pump go out, or anything that would cost you more than it should with overlapping work that’s about to get done. Take a look at my build when I did my headgaskets. This may give an idea.
 

· Former GM Tech and parts
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I would say you’ve been pretty lucky, but I know not all the cp4’s fail either. I made the cp3 swap at like 215k but I’m pretty sure it had been replaced prior to me owning the truck too, which I bought it at 187k. But you getting 415k and not having a problem and not using additives it pretty good I think
 

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2015.5 Chevy 2500HD LML Duramax LTZ Z71
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Id look into the warranties of the parts you're thinking about buying. I replaced my CP4 with the fleece cp3 kit and it has leaked horribly. Paid around $1200 for 3 trips to the shop to fix the leaks. fleece parts come with a pound sand warranty
 

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About to start getting estimates on my 2011 LML head gasket replacement.
What all did you decide to do? Any issues? What did it run ya?
I'm still running my CP4 with 239k, but I see so many post with issues after conversions and that's the luck I'd have.
 

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2011 Silverado 2500 LT2 CCSB, 1 Owner, Deleted @12k, h&s tune, 5” exhaust and a CP3
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550 Posts
I am doing head gaskets right now, I am not doing injectors, water pump, head work on both, both thermostats(even though I had them done about 50k ago but it was cheap) a coolant block off plate on the rear of the block, (it was suggested by the shop) and an S&S cp3
 

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Nice. Keep us posted how it worked out, especially with the conversion. I'm still figuring out which CP3 the look into... Also, considering a lift pump. I love my truck, but like all of us, I only have so much $ to throw at it, so I need to be smart about what and when.
Thanks for the quick reply, too.
 

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2011 Silverado 2500 LT2 CCSB, 1 Owner, Deleted @12k, h&s tune, 5” exhaust and a CP3
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550 Posts
When I talked to my shop it was the better choice for me I don’t have he money really but 2700$ for the S&S CP3 installed vs a FASS and not have the cp4 at all any more was a no brainer deal. I always kept up on filters and usually ran oil of some kind in it’s fuel.

I figured while they had the motor apart it’s now or never. Even with a lift pump it can still fail. A CP3 can fail too though.
 
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