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Hi all,
I recently had a reputable shop replace my radiator with a new Mopar radiator. A day later I was driving to work and I got a check engine light. The code is for a P0128. The most common cause is a faulty thermostat.

I have a couple of questions about this. First, could this have been caused by the shop using two different brands of coolant? They used two coolants that I
provided (Prestone 50/50 and Super Tech 50/50). Would these two coolants being mixed cause an issue?

I know that you are not supposed to mix Prestone with the Mopar coolant, but since it was a new radiator, I'm assuming they flushed the system. Besides, I had been topping off my radiator with Prestone for months, as I have been dealing with a leak, which is why I ultimately had the radiator replaced).

I plan on replacing the thermostat, but I just want to make sure that the coolant that is currently in the system isn't going to continue to cause an issue after the work is done.
 

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Never assume anything. They would not have flushed the system to change the radiator unless you specifically paid to have the system flushed. They would poor back in whatever came out during the rad swap and top it off. Check your work order.
 

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Why did you downgrade coolants? Did you do a complete flush?

Hi all,
I recently had a reputable shop replace my radiator with a new Mopar radiator. A day later I was driving to work and I got a check engine light. The code is for a P0128. The most common cause is a faulty thermostat.

I have a couple of questions about this. First, could this have been caused by the shop using two different brands of coolant? They used two coolants that I
provided (Prestone 50/50 and Super Tech 50/50). Would these two coola being mixed cause an issue?

I know that you are not supposed to mix Prestone with the Mopar coolant, but since it was a new radiator, I'm assuming they flushed the system. Besides, I had been topping off my radiator with Prestone for months, as I have been dealing with a leak, which is why I ultimately had the radiator replaced).

I plan on replacing the thermostat, but I just want to make sure that the coolant that is currently in the system isn't going to continue to cause an issue after the work is done.
 

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Cut the guy some slack. He only has 2 posts.
I would check to see if all of the air has been purged out.

Good luck.
 

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Alldatadiy for P0128...

P0128

P0128-THERMOSTAT RATIONALITY

For a complete wiring diagram,refer to the Wiring Information .

When Monitored and Set Conditions

When Monitored: This diagnostic runs when the following conditions are met:

- With the engine running.

- Start up coolant temperature less than 65°C (149°F).

- Ambient temperature between -8°C (17.6°F) and 50°C (122°F).

- Average vehicle speed greater than 16 km/h (10 mph) until coolant temperature reaches 85°C.

- Engine speed does not go above 5400 rpm for more than 32 seconds.

- The pass/fail determination point is reached when the coolant temp model reaches 88°C (190.4°F).

Set Conditions:

- The predicted coolant temperature reaches the target threshold before the actual coolant temperature and the PCM detects that the actual engine coolant temperature is too far below the what is acceptable for a good thermostat.

Default Actions:

- MIL light will illuminate.




Always perform the PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE before proceeding. See: Testing and Inspection (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

1.LOW COOLANT LEVEL

NOTE:If any ECT or AAT DTCs are present, diagnose and repair those DTCs before continuing with this test procedure.

WARNING:
Never open the cooling system when the engine is hot. The system is under pressure. Failure to follow these instructions can result in personal injury including extreme burns, scalding, or fatal injury. Allow the engine to cool before opening the cooling system.

Check the cooling system to make sure that the coolant is in good condition and at the proper level. See: Engine, Cooling and Exhaust\Cooling System\Testing and Inspection (Refer to 07 - Cooling - Diagnosis and Testing).
Is the coolant level and condition OK?

Yes

- Go To2

No

- Inspect the vehicle for a coolant leak and add the necessary amount of coolant. See: Engine, Cooling and Exhaust\Cooling System\Specifications (Refer to 07 - Cooling - Specifications).

- Perform the POWERTRAIN VERIFICATION TEST. See: Testing and Inspection (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

2.CHECK THE COOLING SYSTEM OPERATION

NOTE:If engine coolant temperature is above 65°C (149°F), allow the engine to cool until it is below 65°C (149°F).

Start the engine.
Check for proper operation of the cooling system while the engine warms up toward operating temperature. Be certain to check the Radiator Cap, flow through the Radiator and anything that can cause a lack of system pressure or lack of coolant flow in the system.
Were any issues found with the cooling system?

Yes

- Perform the appropriate repair in accordance with the Service Information.

- Perform the POWERTRAIN VERIFICATION TEST. See: Testing and Inspection (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).

No

- Replace the thermostat in accordance with the Service Information. See: Engine, Cooling and Exhaust\Cooling System\Thermostat\Service and Repair (Refer to 07 - Cooling/Engine/THERMOSTAT - Removal).

- Perform the POWERTRAIN VERIFICATION TEST. See: Testing and Inspection (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
 

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O.K., This Thread is going nowhere fast.

Based on what info you have given us, which I agree isn't enough for anyone to give you a accurate recommendation of help. Take it in, preferable to your Jeep Dealer, who will install the correct Mopar parts needed. Have them flush your cooling system, and then install a new Mopar thermostat, Radiator cap, and the correct antifreeze. 2012 and back takes HOAT ANTIFREEZE, 2013 and forward JK's takes OAT ANTIFREEZE. One does not ever want to mix these two antifreeze's, because they are not compatible.

When asking for help in the future, its always best to start out with year, and model of your wrangler. Mileage would also be helpful.

Welcome to the Forum, and good luck with your issue.
 
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