P0128 Coolant code on the Forte 2.4L

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🤔 :LOL: So follow up to the oem T-stat replacement thread on the Kia Forte 2.4L. ( https://bobistheoilguy.com/forums/threads/hyundai-kia-2-4l-thermostat-replacement-on-forte.360076/ )
I was greeted with a check engine light (P0128) This am. I replaced the perfectly fine oem working T-stat because it has a few years and some miles on it with a new oem genuine 82C t-stat. also wanted to replace coolant and keep the oem coolant type.. Long story short I had to do the job twice. The first time I put the gasket on the t-stat housing (It did not come off like that, I don't know what I was thinking....) and not the engine block. Then it started to leak under pressure. Drained coolant again disassembled the t-stat housing put the gasket in the correct location on engine block and reassembled.. Filled up coolant bleed the system of air for over a hour then drove it for a day and repeat just to make sure all air was out of system. Triple checked for leaks none are present and it holds pressure perfectly the system.

I did not look at freeze frame data to see what conditions the light was set. But the first drive after the final coolant refil/ t-stat replacement and bleed. I gave it a couple gear wot pull and noticed the temp dropped to 1/4 and heat got cooler. Outside temps were 34F. That was a day or two ago.. I just assumed the T-stat opened and air was expelled. I let the car cool checked level after I started on cold engine and added maybe a cup to radiator. Currently no air bubbles are preset and the temp drop has not occurred again even after wot shifts in 34 degree air. But that's when the the check engine lit up. The engine will register heat within a min of starting and show full operating temperature in about seven minutes even in mid 30's temps. The heat output is really nice no fluctuating or anything like that and its very warm. Same for temperature gauge on the dash it will go to about half not fluctuate one single LCD pixel.

So that background. Could this just be a old code after the thermostat/coolant replacement and the one temp drop that happened? Give me your thoughts on this please. Thanks!.


🙏

IMG_1925.jpeg
 

JTK

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I would think the easiest way to start would be to use a scan tool that will allow you to graph real time data for coolant temp. South Main Auto just did a video on this for a Chrysler pentastar I believe. Very common code he said. Generally the T-stat.
 

1 SX

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A quick update on this. I cleared code yesterday, and it came back today. I did capture the freeze frame data this time.. Is it possible this new t-stat is opening up too soon and over cooling? The car warms up on temp gauge within 4 mins on a cold start, and it never goes down once its warm. Heat is strong, coolant is full with no air. This is FF data:
IMG_1927.jpeg
IMG_1928.jpeg


And here is live data info after a 20 min drive in 50 degree temps this AM. Does anything look off?

IMG_1929.jpeg

IMG_1930.jpeg
IMG_1931.jpeg
IMG_1932.jpeg
 

1 SX

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Did a graph - now im going to have to drive it now with laptop hooked up to see if the temps drop. But it reads about 190F currently.

IMG_1933.jpeg
 

1 SX

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Found the issue. Take a look at the graph and what the car reads.

Car reads this:
IMG_1939.jpeg


BUT, the live data reports this:
IMG_1936.jpeg

On the highway @ 2000 RPMS in 6th it does not go over 143F, even after a WOT accretion, and no heat on.... Let the car idle for a couple minuets and the live data reports 191F. Start driving after 2 miles it back to 143F.

So does this point Lazy/Defective T-stat?

Thanks.
 

twouvakind

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I can go get a new thermostat and give you my old one, I cannot recall when I replaced it but it is problem free at 148k. Never threw a code and my temp gauge is just like yours on my '11 SX.
 

1 SX

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So as a test I covered half the radiator with cardboard and jumped on highway for a few miles. These are the results. I'll order a new T-stat, Coolant, and gaskets and third times the charm haha.

IMG_1940.jpeg


Also after I did this cardboard test, no codes are pending or present.
Last edit, I said heat was strong before.... I was wrong, now its strong.
 
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Are you going to be able to return the defective new one?
Are you absolutely sure it's not a reboxed Motorad? Yes, I remember that you posed pictures of the box.
 
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Did you line the new OE thermostat pointer with the mark in the housing?
Did you clean the temp sensor plug and its harness? Even slightly loose will throw off a reading.

Are you sure that you have the coolant filled up all the way and burped?

I would install a new dealer sourced tested thermostat, with its gasket, with marks lined up correctly, a new temp sender, and verify temp sensors connection.

Some attention to detail is missing and causing your issues. And yes, am hoping that your ECU isn't defective. Might want to verify the software to make sure there weren't and updates.
 

1 SX

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Hey, to update this thread.

I went to the dealer and bought a new genuine OEM 82C thermostat with vin confirmation -$36, oem thermostat gasket - $9 and used kia 50-50 pre made long life coolant - $22 to eliminate most variables..

Drained coolant system for time number 3 via radiator drain plug, removed housing than the old broken t-stat and gasket, reinstalled new dealer t-stat in notch with bleeder facing up and then placed new gasket in grove on engine block, reattached the housing, tighten the 3 ten mm bolts to 9 lbs ft refill coolant via radiator cap opening while squeezing hoses, stated and let engine idle until the engine fans kicked on 5 times while adding coolant and verifying temperature on obd laptop, turned engine off, put cap on radiator start engine up let idle for 5 mins, then went on test drive while observing the thermostat cooling temperatures.

Results: heat output has never been better. Temp reading via obd coolant temp sensor is rock solid stable, no leaks nor air in system.

3rd time is the charm. 🙏
 
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Kia has a 50:50 coolant? Everything I've bought at Hyundai/Kia were full strength coolants. What part number did they sell you?


reinstalled new dealer t-stat in notch with bleeder facing up and then placed new gasket in grove on engine block, reattached the housing,

The thermostat o-ring wraps around the thermostat. Its not something that you place separately after installing a bare thermostat.


thermostat.jpg
 

1 SX

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Kia has a 50:50 coolant? Everything I've bought at Hyundai/Kia were full strength coolants. What part number did they sell you?




The thermostat o-ring wraps around the thermostat. Its not something that you place separately after installing a bare thermostat.


View attachment 121680
I believe on certain models, you are correct, on the forte 2.4L non-direct injected the gasket sits inside a groove on the thermostat housing / engine block.
F4D7DE5D-40C2-4B08-9922-B40AB7114C7D.jpeg


This is the coolant that I bought from Kia
DF88E6BA-7F82-4C86-9943-7FF15E289C53.jpeg
528CA32C-D2E8-424A-A093-61B99E60D479.jpeg


4FC4EE0B-1C46-43C9-9ED4-E8CB207C4203.jpeg

And this is the invoice with the part numbers
CCAE63C1-5BFD-4D97-883B-52A91CD2205A.jpeg
 
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A word of advice: there is a TSB floating around that covers various Hyundai/Kia vehicles regarding a P0128 code. Apparently, the ECU's cooling system logic gets easily confused if the system has anything more than a 50/50 antifreeze mix in the system. Past 50% straight coolant, and the computer can get confused.

I have personally run into this after doing a coolant flush on said vehicles. If the ratio isn't spot on, a code you shall see.
 

1 SX

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Are you going to be able to return the defective new one?
Are you absolutely sure it's not a reboxed Motorad? Yes, I remember that you posed pictures of the box.
I am going to return the defective t-stat. I'm not sure what I bought off amazon, it was listed as genuine OEM 82C H/K T-stat part number 25500 23010. This is the Amazon box t-stat.
IMG_1874.jpeg


and this is the dealer box t-stat.
IMG_2021.jpeg
 
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