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Ask Jake Cheek Your Own Question
Jake Cheek
Jake Cheek,
Category: GMC
Satisfied Customers: 24
Experience:  Automotive Technician at Hendrick Chevrolet
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I have a 2006 gmc 2500hd with the LBZ duramax my truck warms

Customer Question

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: 3 months ago.
Category: GMC
Expert:  david craig replied 3 months ago.

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

Expert:  david craig replied 3 months ago.

heres a couple prints

Customer: replied 3 months 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
Expert:  david craig replied 3 months 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?

Customer: replied 3 months ago.
this started last week this is why I changed them out and recovery tank cap as well
Expert:  david craig replied 3 months 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.

Customer: replied 3 months 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: replied 3 months ago.
Does that temperature sensor affect my climate control it all?
Expert:  david craig replied 3 months 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.

Expert:  david craig replied 3 months ago.

and on some vehicles, theres no affect at all.

Customer: replied 3 months ago.
I just pulled up to my house and noticed antifreeze coming out of my overflow this just keeps getting stranger
Expert:  david craig replied 3 months ago.

not good. overheating?

Expert:  david craig replied 3 months ago.

you sure you installed the t stats correctly?

Customer: replied 3 months ago.
Temp still reads cold
Expert:  david craig replied 3 months ago.

like at the cold mark?

Customer: replied 3 months ago.
Unless I have a massive air lock this is cause for concern now
Expert:  david craig replied 3 months ago.

did you put the t stat in backwards?

Expert:  david craig replied 3 months ago.

i gotta get home. catch you in an hour

Customer: replied 3 months ago.
87F
Customer: replied 3 months ago.
No I didn't I orientated them the same as the stock ones
Customer: replied 3 months ago.
Kk talk to you in a bit
Expert:  david craig replied 3 months ago.

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

Expert:  david craig replied 3 months ago.

any news? update?

Customer: replied 3 months ago.
Haven't had time I'm out hunting today
Expert:  david craig replied 3 months ago.

okey dokey

Expert:  david craig replied 3 months ago.

checking in to see how its going

Expert:  david craig replied 3 months ago.

hello????

Expert:  david craig replied 3 months ago.

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

Customer: replied 3 months ago.
No I've determined it's a bad head gasket
Expert:  david craig replied 3 months ago.

how did you determine that? block test?

Customer: replied 3 months 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: replied 3 months 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
Expert:  david craig replied 3 months ago.

i disagree. your temp would be rising.

Expert:  david craig replied 3 months ago.

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

Expert:  david craig replied 3 months ago.

do a compression test. or a cylinder leak down

Customer: replied 3 months 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: replied 3 months ago.
I put new thermostats in maybe a faulty thermostat?
Customer: replied 3 months ago.
Besides where would you do a compression test on this there's no spark plugs.
Expert:  david craig replied 3 months 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.

Customer: replied 3 months 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.
Expert:  Jake Cheek replied 3 months ago.

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

Customer: replied 3 months ago.
Not sure if you can help
Expert:  Jake Cheek replied 3 months ago.

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

Expert:  Jake Cheek replied 3 months 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.

Expert:  Jake Cheek replied 3 months ago.

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

Customer: replied 3 months 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: replied 3 months 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
Expert:  Jake Cheek replied 3 months ago.

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

Customer: replied 3 months ago.
Ya that was my reason for changing them
Expert:  Jake Cheek replied 3 months ago.

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

Customer: replied 3 months 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
Expert:  Jake Cheek replied 3 months 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!

Customer: replied 3 months 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: replied 3 months ago.
I did do I hydrocarbon test on the coolant and it was negative as well
Expert:  Jake Cheek replied 3 months 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?