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2018 Kia Optima — coolant is old by age but mileage is low

ProjectGeekCommunity StarterNov 15, 20252018 Kia Optima EXFlorida
2018 Kia Optima EX, about 119,500 miles. The vehicle has relatively few miles but the coolant is several years old. I am trying to prioritize maintenance by actual risk. Would you replace based on time alone? I am in Florida.
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11 replies

TruckPilot811Community StarterCommunity StarterNov 15, 2025permalink
Start with the test that can prove you wrong. Move a coil or plug on the 2018 Kia Optima if it's cylinder-specific and see whether the code follows. Save the big job until that test fails. A shop burned me once by skipping that step. Worth doing even if the car feels fine right now. Checking again after work.
QuietLearner245Community StarterCommunity StarterNov 15, 2025permalink
Quick add on that: Capture voltage while the 2018 Kia Optima is actually failing — after it restarts you've lost the clue. If the cheap test changes it, stop and reassess. When does it actually happen? Checking again after work.
ProjectGeekCommunity StarterCommunity StarterNov 16, 2025permalink
OP update: scanned the 2018 Kia Optima again and still only have the one pending code, no new lights. Happens in gear, not in park, for what that's worth.
NewCarMiles252Community StarterCommunity StarterNov 15, 2025permalink
That's a good start, but I wouldn't stop there. Write temp, speed, and in-gear vs coast when the 2018 Kia Optima does it — then decide on parts. If the cheap test changes it, stop and reassess. Post the numbers (or the code) and people can get more specific. Heat soak after errands is the other window.
ProjectGeekCommunity StarterCommunity StarterNov 15, 2025permalink
Tried a second charger / second scan and the story on the 2018 Kia Optima didn't change. I'll poke at it this weekend.
TowDriverCommunity StarterCommunity StarterNov 15, 2025permalink
I'd want a measurement, not a hunch. Swap the cheap/easy piece first on the 2018 Kia Optima and see if the fault moves. That's the branch I'd chase this week. Write the result down so the next test isn't a repeat of the last one. Parking it somewhere I can hear it better next time.
PistonRoadie235Community StarterCommunity StarterNov 15, 2025permalink
Ask what changed right before it started. If a shop can't duplicate it on the 2018 Kia Optima, bring a video plus freeze-frame data, not just a story. That's the branch I'd chase this week. This is from a 2018 Kia Optima in Florida with 119,500 miles. If it doesn't change the out-the-door or the repair estimate, it's noise. No warning lights, which is why I'm documenting it.
BoxerPilot91Community StarterCommunity StarterNov 15, 2025permalink
Log the conditions before you spend. Loaded-suspension checks on the 2018 Kia Optima catch play that a wheels-hanging inspection misses. Save the big job until that test fails. On “coolant is old by age but mileage,” that was the fork that mattered for me. Not gospel, but it saved me a headache. Doing the boring step first on purpose.
CityMom597Community StarterCommunity StarterNov 16, 2025permalink
If it were in my driveway, move a coil or plug on the 2018 Kia Optima if it's cylinder-specific and see whether the code follows. You'll know quickly if you're on the wrong tree. I'd want that in writing, not as a promise. I'd sleep better after that step, even if it finds nothing. This is the version I'd tell a friend.
CityMom597Community StarterCommunity StarterNov 16, 2025permalink
Ask what changed right before it started. Loaded-suspension checks on the 2018 Kia Optima catch play that a wheels-hanging inspection misses. That's the branch I'd chase this week. Verbal 'we'll take care of it' is not a plan. If the story changes I'll post the new data.
ProjectGeekCommunity StarterCommunity StarterNov 16, 2025permalink
OP update: scanned the 2018 Kia Optima again and still only have the one pending code, no new lights. Cold start is when I can actually reproduce it.
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