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Duramax Fifth Generation: 2011-2016 (LML) Discuss the fifth generation (2011-2016) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 12-18-2018, 01:27 AM   #11 (permalink)
Dmax Dually
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Quote:
Originally Posted by theZman View Post
Picked up a set of thermostats today, gonna change em out tomorrow


Sent from my iPhone using Tapatalk
Our trucks have 2 thermostats?? Do all diesels have 2 or just the DuraMaxes?? Why 2 thermostats?

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Old 12-18-2018, 09:25 AM   #12 (permalink)
G2GBY
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Quote:
Originally Posted by Dmax Dually View Post
Our trucks have 2 thermostats?? Do all diesels have 2 or just the DuraMaxes?? Why 2 thermostats?
How our Thermostates work together.
Here is the official GM explanation of how the different components work.

Basically they are trying to keep the engine within the optimal operating temp range by manipulating flow via specific temperatures. This should explain why the 2 different range t-stats

Cooling Cycle (6.6L Diesel Engine)

Coolant is drawn from the radiator outlet and into the water pump inlet by the water pump. The coolant flows to the heater core while the engine is running. This provides the passenger compartment with heat and defrost.
Coolant is then pumped through the water pump outlet and through the coolant pipe to the engine oil cooler. The coolant flows around the oil cooler element and to the rear engine cover. The rear engine cover distributes the coolant flow to both banks of the engine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.
The coolant is then forced through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.
Coolant is also directed to the turbocharger. There it circulates through passages in the center housing. During engine warm-up cycle the bypass valve located in the turbocharger inlet hose at the outlet pipe prevents coolant flow. During normal operating temperatures, the coolant assists in keeping the turbocharger cool.
From the cylinder heads, the coolant flows to the thermostats. The coolant flows from the thermostat housing to the water pump through the bypass pipe until the enginereaches 85C (185F).
Operation of the cooling system requires proper functioning of all cooling system components. The cooling system consists of the following components:

Thermostats (6.6L Diesel Engine)

The thermostats are coolant flow control components. The purpose of the thermostats are to regulate the correct operating temperature of the engine. The thermostats utilizes a temperature sensitive wax-pellet element. The element connects to a valve through a piston. When the element is heated, it expands and exerts pressure against a rubber piston. This pressure forces the valve to open. As the element is cooled, it contracts. This contraction allows a spring to push the valve closed.
The 6.6L diesel engine requires two thermostats for correct coolant flow. The front thermostat is a dual purpose thermostat. The front thermostat controls the coolant flow to the bypass port and to the water outlet. The rear thermostat only controls the coolant flow to the water outlet.
When the coolant temperature is below the rated thermostat opening temperature, the front thermostat valve remains closed to the water outlet and is opened to the bypass port. The bottom portion of the thermostat is raised off of the bypass port while at the same time the top portion closes the coolant flow to the water outlet. The rear thermostat also is closed to the water outlet during engine warm-up. This prevents circulation of the coolant to the radiator and allows the engine to warm up quickly. After the coolant temperature reaches 82C (180F) the front thermostat primary valve opening temperature, the front thermostat primary valve will start to open. The coolant is then allowed to circulate through the thermostat to the radiator where the engine heat is dissipated to the atmosphere. As the engine coolant reaches 85C (185F) and more coolant demand is required the front thermostat secondary valve begins to close the bypass port and the rear thermostat begins to open coolant flow to the water outlet. The thermostats will continue to control the coolant flow by opening and closing. The front thermostat will be fully open when the coolant temperature reaches 95C (203F) the rear thermostat will be fully open when the coolant temperature reaches 100C (212F). The thermostat also provides a restriction in the cooling system, even after the it has opened. This restriction creates a pressure difference which prevents cavitation at the water pump and forces coolant to circulate through the engine block

Engine Oil Cooler (6.6L Diesel Engine)

The engine oil cooler is a heat exchanger. The engine oil cooler is mounted to the left lower corner of the engine. The oil filter is attached to the oil cooler housing. The engine coolant flows around the oil cooler element. The oil cooler element is a series of plates. The engine oil temperature is regulated by the temperature of the engine coolant that surrounds the oil cooler as the engine oil passes through the cooler.
The engine oil pump, pumps the oil through the engine oil feed line to the oil cooler. The oil then flows down through the cooler while the engine coolant absorbs heat from the oil. The oil is then pumped through the oil return line, to the oil filter, then to the main engine oil passage.

Turbocharger Bypass Valve (6.6L Diesel Engine)

The turbocharger bypass valve is a temperature control valve. The valve is located in the turbocharger coolant inlet hose at the water outlet tube.
The purpose of the valve is to close the coolant flow through the turbocharger. Closing off the coolant flow through the turbocharger avoids turbocharger overcooling.

You can buy aftermarket Thermostates higher or lower to suite your needs. Most people use these (Mishimoto)

Do all Diesels have two Thermostates
https://www.agriculture.com/machiner...wo-thermostats


Last edited by G2GBY; 12-18-2018 at 09:48 AM.
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Old 12-18-2018, 09:51 AM   #13 (permalink)
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Great, thanks for the info. Being my first diesel I never knew. As a kid I grew up on plugs, points, condenser & carburetors. Thanks
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Old 12-18-2018, 12:22 PM   #14 (permalink)
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Just dealt with this on my 2012 right at 100k mi. New thermostats and coolant flush and temps are back where they should be.
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Old 12-19-2018, 10:06 PM   #15 (permalink)
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Had this about 3 months ago on my '12 with about 150k miles. Easy fix though and less than $100.
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Old 12-23-2018, 12:00 AM   #16 (permalink)
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Hello. New member here. Did not find info on this issue so I want to share. I have a 2011 LML built before October 2011. Over a 3 week period I learned that should a radiator hose fail resulting in a large coolant loss there is a TSB that requires a new hose assembly to be installed. TSB 11-06-02-002A is the solution. Without these changes to the coolant reservior, heater hose, and the hose from the coolant reservoir to the radiator the coolant reservoir will blow coolant from the low pressure side. The fix, at the dealer was under $400. They did not know about the TSB. The internet is a wonderful thing.
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Old 12-23-2018, 01:24 AM   #17 (permalink)
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Unless you live in a rural farming or agriculteral area where diesel pickups are widely used and sold it is very hard to find a dealership with knowledgeable experience diesel tech to work on our trucks. The majority of them are just auto techs with a diesel rating that rarely work on diesels. Many times I had to show them TSB's and explain things on my truck.
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Old 12-23-2018, 01:28 PM   #18 (permalink)
dmax3500
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in 30-40deg weather my 2013 unloaded will run 185,but idling thru traffic or sitting still it runs 150-160,these trucks have huge rads,and just don't make the heat


truck runs fine and im just going to leave it alone
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Last edited by dmax3500; 12-23-2018 at 01:29 PM.
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Old 03-08-2019, 12:54 PM   #19 (permalink)
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I just threw a P0128 code, but My gauge in Looks like it is running about 200 F. Can I still have a bad thermostat?

Also I see on youtube lots of LLY videos but none for the LML is it the same??
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Old 03-08-2019, 01:52 PM   #20 (permalink)
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Quote:
Originally Posted by mastercraftka View Post
I just threw a P0128 code, but My gauge in Looks like it is running about 200 F. Can I still have a bad thermostat?
Also I see on youtube lots of LLY videos but none for the LML is it the same??
Basically all the same.
P0128
https://www.dieselplace.com/forum/63...074-p0128.html
Most likely your truck doesn’t meet the calibrated target temperatures. Do you have the capability to freeze frame when code is set?


Last edited by Rvn4me; 03-08-2019 at 01:55 PM.
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