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P0128 Code 2006 4.0

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Old 11-23-2013, 09:02 AM
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SLVRSTNG06
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Default P0128 Code 2006 4.0

Car threw a check engine light yesterday on a long drive.. scanned it and got p0128. Noticed the engine temp gauge would not fully go to normal operating temperature. Do I need to change my thermostat?
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Old 11-23-2013, 02:10 PM
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Art161
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It couldn't hurt to change the thermostat. If you are still using a plastic housing, you might want to take this opportunity to replace it with a metal one.

Edit: There's also the possibility that the cooling fan is running when the coolant temperature is not hot enough to warrant that.

Last edited by Art161; 11-23-2013 at 02:22 PM. Reason: Additional thought.
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Old 11-23-2013, 09:11 PM
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SLVRSTNG06
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changed the thermostat today.. very easy took me all of 20 minutes and the car is running at normal temperature again. my only concern was before i changed the thermostat this morning my coolant reservoir tank was dead empty with the engine cold. I filled it up before the thermostat change and it didn't solve the problem so i then changed the thermostat and everything seems alright. Just wondering where my old coolant went, i have zero leaks but did drive the car 300 miles yesterday with this thermostat issue, did the coolant get evaporated due to the engine being in fail safe mode??
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Old 11-23-2013, 10:48 PM
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I don't think the coolant would have evaporated due to a faulty thermostat that was causing a low temperature. Keep an eye on the level in the reservoir (degas bottle).
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Old 11-24-2013, 01:40 AM
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p0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

Check out http://www.obd-codes.com/p0128 for more info.
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Old 11-24-2013, 09:51 AM
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If your bottle is empty then you are losing coolant somewhere, it doesn't just evaporate.

Take another look at the thermostat housing - and look for signs of leakage toward the back. The split usually happens on the back of the housing and the coolant goes into the valley under your intake manifold.
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Old 11-24-2013, 04:45 PM
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Just looked under the hood again today when the engine was cold, tank was empty again no coolant.. looked around the thermostat housing seems like it must be cracked as i can see some coolant underneath by the intake manifold- looks like i need to change the housing, wish i could wait for a metal one as i see a group buy thread but i need my car running asap so I'm headed to the dealership parts dept tomorrow.
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