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I have a 2006 gmc 2500hd with the LBZ duramax my truck warms

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up to 56°C (132°F)...
I have a 2006 gmc 2500hd with the LBZ duramax my truck warms up to 56°C (132°F) then the temp drops to 28°C (82°F) then after driving for a bit it will shoot up to normal operating temperature it will level out at around 85°C and then it will fluctuate between 85 (185°F) and 88°C (190°F) this morning I got an engine light the trouble code is PO128 coolant thermostat ( coolant temperature below thermostat regulating temperature) the thermostats are both new and it has a new recovery tank cap. This morning it hasn't gone above 31°C (87°F) I'm stumped maybe possible air l9ck?
Submitted: 1 year ago.Category: GMC
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Answered in 2 hours by:
11/4/2016
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago
david craig
david craig, Owner/[email protected] 3D Atuomotive
Category: GMC
Satisfied Customers: 4,034
Experience: owner/mechanic at 3D Automotive
Verified

Hi Im David, yes possible air in the system, possible intermittent temp sensor or temp sensor wiring

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Customer reply replied 1 year ago
that would cause me to lose heat in the cab as well I also heard it could be a head gasket but it isn't displaying any of the major symptoms of a head gasket I'm a journeyman Millwright so I know my way around a diesel this is just a little more complicated then the diesels I'm used to working on
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

you didnt say it was losing heat in the cab. and if it was a head gasket, you would be overheating and not fluctuating. were the thermostats replaced due to this issue or was it due to something else?

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Customer reply replied 1 year ago
this started last week this is why I changed them out and recovery tank cap as well
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

so basically you have a temp gauge that has no ides where its at. make sure the system is full of coolant, bleed the air out of it if any, then while someone is inside the cab do a wiggle test on the wiring to the temp sensor to see if it jumps around.

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Customer reply replied 1 year ago
I'm getting the same reading from my bully dog gauge GT the digital read out is the same as my gauge not sure if that has any bearing on it
Customer reply replied 1 year ago
Does that temperature sensor affect my climate control it all?
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

usually the coolant temp sensor affects all kinds of inputs and outputs to the computer to compensate for different readings whether its climate control or mass airflow and a few others, so yes, indirectly it will affect it.

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

and on some vehicles, theres no affect at all.

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Customer reply replied 1 year ago
I just pulled up to my house and noticed antifreeze coming out of my overflow this just keeps getting stranger
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

not good. overheating?

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

you sure you installed the t stats correctly?

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Customer reply replied 1 year ago
Temp still reads cold
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

like at the cold mark?

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Customer reply replied 1 year ago
Unless I have a massive air lock this is cause for concern now
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

did you put the t stat in backwards?

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

i gotta get home. catch you in an hour

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Customer reply replied 1 year ago
87F
Customer reply replied 1 year ago
No I didn't I orientated them the same as the stock ones
Customer reply replied 1 year ago
Kk talk to you in a bit
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

87??? WOW. take the temp sensor out and put aa heat gun to it. see what the gauge does.

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

any news? update?

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Customer reply replied 1 year ago
Haven't had time I'm out hunting today
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

okey dokey

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

checking in to see how its going

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

hello????

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

do you still need assistance or not????????????

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Customer reply replied 1 year ago
No I've determined it's a bad head gasket
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

how did you determine that? block test?

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Customer reply replied 1 year ago
Because I'm getting pressure huge pressure build up in my cooling system I used a snap on bleed tool to removed any air in the system. My coolant temperature keeps dropping after driving for 5 minutes and that makes sense the only thing I couldn't get a sucessful test for hydrocarbons in my coolant everything seems to point to a bad head gasket
Customer reply replied 1 year ago
I really didn't want to change it out as it is a 32 hour job according to the flat rate book but if that's the issue then new gaskets and ARP stud kit it is
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

i disagree. your temp would be rising.

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

white exhaust smoke?, coolant in oil? rising temps?

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GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

do a compression test. or a cylinder leak down

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Customer reply replied 1 year ago
Well I'm lost then I was told about a legendary duramax mechanic that lives in a town not far from me I may go visit. Unless you can give a definitive answer I mean this has to be tough for you not having the vehicle in front of you
Customer reply replied 1 year ago
I put new thermostats in maybe a faulty thermostat?
Customer reply replied 1 year ago
Besides where would you do a compression test on this there's no spark plugs.
GMC Mechanic: david craig, Owner/[email protected] 3D Atuomotive replied 1 year ago

ill opt out cause we aint seeing eye to eye on this so take it to your diesel guy. lets just agree to disagree my friend. good luck to you.

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Customer reply replied 1 year ago
Lmao! Ok thanks I think we are locking horns is I'm a industrial mechanic and I keep drawing my own conclusions because I'm used to troubleshooting and brainstorming and I'm also stubborn as I'm sure it shows I'll try that guy I hope your right that it isn't a head gasket have a good day.
GMC Mechanic: Jake Cheek,
 replied 1 year ago
Jake Cheek
Category: GMC
Satisfied Customers: 26
Experience: Automotive Technician at Hendrick Chevrolet
Verified

Hi my name is***** you still requiring assistance?

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Customer reply replied 1 year ago
Not sure if you can help
GMC Mechanic: Jake Cheek,
 replied 1 year ago

I can try. The truck doesn't come to operating temperature and no heat?

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GMC Mechanic: Jake Cheek,
 replied 1 year ago

If the radiator was replaced for a cooling system concern, or replaced during a front end body shop repair, it may be missing the radiator surge tank restriction orifice. Remove the surge tank hose from the radiator and visually inspect the radiator tank nipple that feeds the surge tank. If the radiator is missing the surge tank restriction orifice there will be an increased amount of coolant flow to the surge tank. Excessive coolant flow may induce DTC P0128.

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GMC Mechanic: Jake Cheek,
 replied 1 year ago

If the radiator surge tank restriction is missing, the radiator needs to be replaced with the proper replacement radiator.

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Customer reply replied 1 year ago
Yep that's the problem some of the time it has new thermostats the rad is original the surge tank has never been removed this just started after parking my truck for a few weeks my truck will also come up to temp and then drop off and then I lose heat
Customer reply replied 1 year ago
Or it will hold operating temperature and run flawless then I'll shut it off and it will act up after a few hours of sitting
GMC Mechanic: Jake Cheek,
 replied 1 year ago

Okay. And did you replace the thermostat for this issue? Or has this happened after the fact?

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Customer reply replied 1 year ago
Ya that was my reason for changing them
GMC Mechanic: Jake Cheek,
 replied 1 year ago

Okay let me do some digging and I will get back with you in a moment!

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Customer reply replied 1 year ago
I know it's not an airlock of any sort because I use the snap on bleeding tool to pull the coolant into the system and then attach the funnel filled it with antifreeze and ran it
GMC Mechanic: Jake Cheek,
 replied 1 year ago

The truck needs head gaskets. You can confirm with a block test and let it run for an hour to an hour and a half. Sorry to be the barer of bad news!

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Customer reply replied 1 year ago
Well ARP studs and new gaskets I tried to tell the other mechanic I talked I suspected gaskets and he argued that it wasn't
Customer reply replied 1 year ago
I did do I hydrocarbon test on the coolant and it was negative as well
GMC Mechanic: Jake Cheek,
 replied 1 year ago

I have a feeling this may be in the early stages. You may need to run the hydrocarbon test again. If that doesn't show anything an extended block test (1 - 1.5 hrs) will show exhaust gases in the cooling system. Is there anything else I can help you with?

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Jake Cheek
Jake Cheek
Jake Cheek
Category: GMC
Satisfied Customers: 26
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Experience: Automotive Technician at Hendrick Chevrolet

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