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Hey guys I’m new to the duramax world anyways had the truck for about 3-4 months no issues really it’s an 05. Anyways I’m scared of the fact that my truck might need HG’s. here’s what I have so far: last night and the day before I noticed a puddle of anti-freeze under the truck. Upon further investigation looks like it’s coming out of the overflow in the resivoir, but anyways I let the truck sit overnight and the upper rad hose is like a tennis ball now I tried to take the resivoir cap off and it just wanted to push antifreeze out so it’s got pressure in the bottle, I tried to bleed the system at the thermostats and no air came out. So I’ve got my fingers crossed on a bad cap on the resivoir but I need some more insight from someone who’s more experienced with this, any help would be great, thanks


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Hey guys I’m new to the duramax world anyways had the truck for about 3-4 months no issues really it’s an 05. Anyways I’m scared of the fact that my truck might need HG’s. here’s what I have so far: last night and the day before I noticed a puddle of anti-freeze under the truck. Upon further investigation looks like it’s coming out of the overflow in the resivoir, but anyways I let the truck sit overnight and the upper rad hose is like a tennis ball now I tried to take the resivoir cap off and it just wanted to push antifreeze out so it’s got pressure in the bottle, I tried to bleed the system at the thermostats and no air came out. So I’ve got my fingers crossed on a bad cap on the resivoir but I need some more insight from someone who’s more experienced with this, any help would be great, thanks


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Also I was just sitting in the truck at idle for about 20 minutes or so last night and wouldn’t get warmer then 155 then all of a sudden started to loose engine temp right away and came back up right away after driving the truck home


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If you still have pressure in the system after driven, and sitting over night-- you have classic signs of a bad head gasket. I doubt it is a bad cap. Most are in denial when they have the signs of a bad head gasket. The coolant dye test, or a compression usually do not show early signs of a bad gasket, nor does the Duramax dump coolant in the crankcase.
 

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If you still have pressure in the system after driven, and sitting over night-- you have classic signs of a bad head gasket. I doubt it is a bad cap. Most are in denial when they have the signs of a bad head gasket. The coolant dye test, or a compression usually do not show early signs of a bad gasket, nor does the Duramax dump coolant in the crankcase.


Okay thanks for the reply, what’s the best route to go with parts or kits or other mods to do while I’ve got the thing apart


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Xxx

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When I did mine I did factory c-grade gaskets, arp headstuds, water pump, fuel pressure relief valve race plug, fuel pressure regulator, glow plugs, and belt. If you want to do manifolds, up-pipes, or downpipe, now would be the time.
 

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Okay thanks for the reply, what’s the best route to go with parts or kits or other mods to do while I’ve got the thing apart


We can help you out here at LDS with everything you need to complete the job correctly and at an affordable price! Let me know, but sounds like your having HG issues to me.
 

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When I did mine I did factory c-grade gaskets, arp headstuds, water pump, fuel pressure relief valve race plug, fuel pressure regulator, glow plugs, and belt. If you want to do manifolds, up-pipes, or downpipe, now would be the time.


Okay and did you do the work in truck or pull the engine because I was thinking of just taking the grille and the rest behind it to do the job but I’ve heard doing in truck is a pain in the ass


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Nope. That's just oil vapor residue from the crankcase vent system.

Another HG clue is, a flaky heater. No heat, no rise in ECT, then a spike, gush coolant, and then the heater kicks in.

Make for easier access; remove both front wheels and lower frame to ground as much as possible. There's also a 2nd hole in the hood hinge, allowing you to kick the hood up vertical and out of the way, vs removing it entirely.

Edit; is that still the OEM turbo inlet duct I see in the pic?
If it is, need to update that too.
 

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Nope. That's just oil vapor residue from the crankcase vent system.

Another HG clue is, a flaky heater. No heat, no rise in ECT, then a spike, gush coolant, and then the heater kicks in.

Make for easier access; remove both front wheels and lower frame to ground as much as possible. There's also a 2nd hole in the hood hinge, allowing you to kick the hood up vertical and out of the way, vs removing it entirely.

Edit; is that still the OEM turbo inlet duct I see in the pic?
If it is, need to update that too.


Is it worth taking the fenders off? And if you’re talking about the thing that 6.6 duramax yeah I just plugged that hole with a 2”cap just now was waiting for a chance to take it off now was that chance lol


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Turbo Inlet Duct (a.k.a. Mouthpiece), it's what that venting hose attaches to.

In trying to squeeze in the new EPA required EGR on the LLY motor, they made a big design mistake with the 3rd section of the intake.
It's flawed, with a ridge from the casting protruding up and into the air flow.

Highly restrictive, under load it causes a domino effect on a myriad of things (one theory is HG failure/overheating). GM (probably with some insight from Garrett) quickly redesigned that intake the following year with the next generation (LBZ) DMAX.

In the pic below, the OEM duct is on the right, the new design LBZ's on the left, with the duct for the Topkick/Kodiak version in the center (it doesn't have the 2nd inlet on it for the turbo noise cancelling plastic piece with the 6.6 on it).

Big difference between the two....and you're truck will luv ya once it's updated.

Note also in how you 'capped' that inlet off. There's suction on that inlet, Using the wrong setup can decay over time and be sucked into the Turbo. :surprise:



You can easily see the difference between the two when you pop the hood.

LBZ intake


Modified LLY intake, with the new inlet duct
 

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Discussion Starter #15
Turbo Inlet Duct (a.k.a. Mouthpiece), it's what that venting hose attaches to.

In trying to squeeze in the new EPA required EGR on the LLY motor, they made a big design mistake with the 3rd section of the intake.
It's flawed, with a ridge from the casting protruding up and into the air flow.

Highly restrictive, under load it causes a domino effect on a myriad of things (one theory is HG failure/overheating). GM (probably with some insight from Garrett) quickly redesigned that intake the following year with the next generation (LBZ) DMAX.

In the pic below, the OEM duct is on the right, the new design LBZ's on the left, with the duct for the Topkick/Kodiak version in the center (it doesn't have the 2nd inlet on it for the turbo noise cancelling plastic piece with the 6.6 on it).

Big difference between the two....and you're truck will luv ya once it's updated.

Note also in how you 'capped' that inlet off. There's suction on that inlet, Using the wrong setup can decay over time and be sucked into the Turbo. :surprise:



You can easily see the difference between the two when you pop the hood.

LBZ intake


Modified LLY intake, with the new inlet duct


Okay thank you for the helpful tips!


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I pulled the hood of and the fender liners. I then just removed the fan clutch and shroud. After that there was plenty of room around the front and sides of the motor to work. I did mine with the motor in and the cab still on. The biggest pain is getting the down pipe, up-pipes, and manifolds unbolted. There is room, just cant see what your doing. I believe the up-pipes are a 12 point 12 mm. So shallow and deep sockets to fit different situations and i used a swivel 3/8 ratchet. Then the driver side valve cover has an allen head bolt that is really close to the cab. I had to use a swivel ratchet to reach it. Then when you pull the head on the driver side the rear head studs have to be left in the head because they wont clear the cab to come out. Then just make sure to put in head before putting back on motor. The valves will need to be adjusted so search the forms for a how to and make sure to have a good feeler gauge. I would recommend replacing the injector return lines even if they look good. Upon first start up, i had one leaking. Pain to do after all assembled for a 50 dollar part. Keep track of everything and what position it was in. Once the electrical and intake tubes are removed it looks a lot simpler. took about 50 hrs after all said and done by myself. I work at a body shop so i just sourced most of the parts from gm due to having an account.
 

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I pulled the hood of and the fender liners. I then just removed the fan clutch and shroud. After that there was plenty of room around the front and sides of the motor to work. I did mine with the motor in and the cab still on. The biggest pain is getting the down pipe, up-pipes, and manifolds unbolted. There is room, just cant see what your doing. I believe the up-pipes are a 12 point 12 mm. So shallow and deep sockets to fit different situations and i used a swivel 3/8 ratchet. Then the driver side valve cover has an allen head bolt that is really close to the cab. I had to use a swivel ratchet to reach it. Then when you pull the head on the driver side the rear head studs have to be left in the head because they wont clear the cab to come out. Then just make sure to put in head before putting back on motor. The valves will need to be adjusted so search the forms for a how to and make sure to have a good feeler gauge. I would recommend replacing the injector return lines even if they look good. Upon first start up, i had one leaking. Pain to do after all assembled for a 50 dollar part. Keep track of everything and what position it was in. Once the electrical and intake tubes are removed it looks a lot simpler. took about 50 hrs after all said and done by myself. I work at a body shop so i just sourced most of the parts from gm due to having an account.
Also take the wheels off and drop the front down.

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