VOLUNTARY EMISSIONS SERVICE CAMPAIGN: THETA II 2.4L GDI EMISSIONS: ECM LOGIC IMPROVEMENT (SC340 REVISION 5) - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information to upgrade the Electronic Control Module ‘ECM’ system software for certain 2016-2020MY Optima, 2016-2020MY Sorento, 2017-2022MY Sportage vehicles equipped with 2.4L Theta II engines listed in the table below. Kia has become aware that certain 2016-2022MY vehicles equipped with 2.4L Theta II engines may have engine calibrations that were not optimized for emissions standards under certain specific co
full bulletin at NHTSA ↗2018 Kia Optima engine problems
severe Owners of the 2018 Kia Optima have filed 103 NHTSA complaints about the engine, typically surfacing around 77,200 miles at roughly $3,100 to repair (U.S. federal records, as of July 2026). Source: NHTSA Office of Defects Investigation. See engine across all vehicles →
Failure mileage
Complaints
103
Recalls
0
Avg fix
$3,100
| Model year | engine complaints |
|---|---|
| 2014 Optima | 215 |
| 2015 Optima | 451 |
| 2016 Optima | 313 |
| 2017 Optima | 125 |
| 2018 Optima (this page) | 103 |
| 2019 Optima | 60 |
| 2020 Optima | 66 |
1crash
6fires
When does it fail?
Of the 103 engine complaints filed for the 2018 Kia Optima, here's the actual mileage breakdown — failures cluster heaviest at 100,000-125,000 mi.
0-25k
25-50k
50-75k
75-100k
100-125k
125-150k
150k+
Each bar shows the share of total complaints filed at that mileage range. Peak failure window highlighted. Some owners report problems earlier; some make it well past 150,000 miles symptom-free. Maintenance habits and driving conditions shift the curve as much as mileage alone.
What stands out
Engine accounts for 45% of every owner complaint on file for this vehicle — the dominant problem area across 9 categories tracked.
Owners have filed 103 engine complaints with NHTSA against this vehicle, but no formal recall covers the issue — the federal record reflects what manufacturers have admitted, not everything owners are reporting.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering engine on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
VOLUNTARY EMISSIONS SERVICE CAMPAIGN: OWNER NOTIFICATION (SC340 FLIGHT 104 ) - This document is the owner notification advising that Kia is conducting a Voluntary Emissions Service Campaign to improve the emissions software logic in the Electronic Control Module (ECM) for certain 2016-2020 MY Optima vehicles equipped with 2.4L Gas Direct Injection (GDI) engines to ensure compliance with emissions regulations.
full bulletin at NHTSA ↗TECHNICAL SERVICE BULLETIN: VOLUNTARY EMISSIONS SERVICE CAMPAIGN: THETA II 2.4L GDI EMISSION SECM LOGIC IMPROVEMENT (SC340 REV 4) - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information to upgrade the Electronic Control Module ‘ECM’ system software for certain 2016-2022MY vehicles equipped with 2.4L Theta II engines listed in the table below. Kia has become aware that certain 2016-2022MY vehicles equipped with 2.4L Theta II engines may have engine calibrations that were not optimized for emissions standards under certain specific conditions. These calibrations
full bulletin at NHTSA ↗VOLUNTARY EMISSIONS SERVICE CAMPAIGN: OWNER NOTIFICATION (SC340 FLIGHT 103 / JF) - This document is the owner notification advising that Kia is conducting a Voluntary Emissions Service Campaign to improve the emissions software logic in the Electronic Control Module (ECM) for certain 2016-2020 MY Optima vehicles equipped with 2.4L Gas Direct Injection (GDI) engines to ensure compliance with emissions regulations.
full bulletin at NHTSA ↗TECHNICAL SERVICE BULLETIN: VOLUNTARY EMISSIONS SERVICE CAMPAIGN: THETA II 2.4L GDI EMISSIONS ECM LOGIC IMPROVEMENT (SC340) - This bulletin has been revised to include additional information. New/revised sections of this bulletin are indicated by a black bar in the margin area. This bulletin provides information to upgrade the Electronic Control Module ‘ECM’ system software for certain 2016-2022MY vehicles equipped with 2.4L Theta II engines listed in the table below. Kia has become aware that certain 2016-2022MY vehicles equipped with 2.4L Theta II engines may have engine calibrations that were not optimized for emissions standards under certain specific conditions. These calibrations may c
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
The 2018 Kia Optima 2.4L Theta II GDI engine exhibits a pattern of excessive oil consumption without external leaks, beginning as early as 10,000 miles but typically evident after 40,000–100,000 miles. Owners report adding 1–3+ quarts per 1,000 miles and having oil wells consume multiple quarts per week. No external leaks are found despite mechanic inspection, pointing to internal wear.
Secondary failures follow: oil fouls spark plugs, causing misfires in specific cylinders (cylinder #3 or #4 most common), which recur after plug replacement. Combustion cleaning provides temporary relief (3 months) but does not address the root cause. Many owners then experience engine stalling—sometimes with warning (check engine light, rough shaking) but often with no warning—leading to sudden loss of power during highway driving. Dealership diagnostics reveal internal compression loss, rod bearing wear, or fractured valves; permanent repair requires engine replacement ($6,000–$7,300).
Two owners report underhood fires at 22,000 miles. Kia's response includes recall campaigns (SC218Y3, 17V-224) addressing knock sensor codes and ECU software updates, yet these repairs do not resolve underlying oil consumption. Warranty and goodwill engine-replacement programs are frequently denied based on mileage, disputed maintenance claims, second-owner status, or lack of specific diagnostic codes. Owners report being directed between dealership and Kia consumer affairs without resolution, and parts availability (e.g., catalytic converters) can delay repairs 2+ years.
Same Kia Optima engine reports on nearby years: 2015 · 2016 · 2017 · 2019 · 2020
Failure modes owners describe
Excessive Oil Consumption / Internal Engine Wear
2.4L Theta II GDI engine consuming oil at rates of 1–3+ quarts per 1,000 miles without external leaks. Consumers report adding oil weekly to several times per week. Root cause attributed to bearing clearance defects and internal combustion issues. Multiple owners document consumption confirmed by dealership oil-consumption tests.
When: Typically begins 40,000–100,000 miles; some cases documented as early as 10,000–22,000 miles on used/CPO purchases.
Symptoms owners cite: Oil level dropping 1–3 quarts per 1,000 miles; No visible external leaks despite mechanic inspection; Check engine light and oil warning lights illuminating; Elevated oil consumption test results (1 qt/1,000 mi or higher); Oil visible in tailpipe upon acceleration
Codes mentioned: P1326 (knock sensor/rod bearing wear)
Repairs/costs cited: Dealership-recommended fixes include combustion chamber cleaning ($650+, temporary; repeat needed in 3 months). Permanent solution requires engine replacement ($6,000–$7,000+ estimated by owners). Many owners cite parts unavailability and long lead times (up to 2 years reported for catalytic converters).
Recalls/TSBs owners mention: Class-action lawsuit (mentioned in multiple complaints) covers rod bearing defects under KSDS campaign; however, coverage terms require engine seizure/compression loss or rod failure to qualify. Extended warranty mentioned but disputed scope (some dealers claim rod bearing coverage only, not compression). GDI recalls 17V-224, SC147, SC172, SC218 cited but many 2018 Optimas excluded despite matching symptoms. Goodwill engine replacement programs declined on grounds of mileage, maintenance records, or lack of specific diagnostic codes.
Oil Leaking onto Spark Plugs / Misfire / Fouling
Oil contamination of spark plugs and ignition coils, causing misfires in specific cylinders (most commonly cylinder #3 or #4 reported). Oil leaks into spark plug wells without visible external leakage. Misfire triggers limp mode or stalling; recurs after plug replacement.
When: Develops after excessive oil consumption established; misfires reported from ~70,000 miles onward but tied to underlying consumption issue that begins earlier.
Symptoms owners cite: Check engine light with P0300-series misfire codes; Rough idle or hesitation during acceleration; Car shaking or vibrating; Fouled spark plugs visible with oil residue; Misfire in same cylinder after prior repair (recurring issue within 1 year)
Codes mentioned: P0300 (Random/Multiple Cylinder Misfire), P0303, P0304 (Cylinder-specific misfire)
Repairs/costs cited: Immediate repair: spark plug and ignition coil replacement ($~150–400 per service). Temporary mitigation: upper engine combustion cleaning ($650+). Owners report misfires recurring 3–12 months after cleaning. Permanent fix requires addressing root cause (oil consumption/engine replacement).
Recalls/TSBs owners mention: Dealers perform spark plug and combustion cleaning per TSB ENG 222; however, fixes are temporary. Warranty typically does not cover this as secondary wear if engine is out of warranty. Some dealers have refused to perform recommended TSBs, citing mileage or maintenance records.
Engine Seizure / Catastrophic Internal Failure
Complete loss of engine compression, stalling, or mechanical seizure. Often preceded by prolonged excessive oil consumption. Results in total engine failure requiring replacement. Cylinder failure, rod bearing blow-through, and valve fracture reported.
When: Occurs after months to years of elevated oil consumption; mileage range 57,000–146,000 miles at time of failure.
Symptoms owners cite: Sudden stall without warning or with only brief hesitation preceding; Loud engine knock or noise immediately before failure; Complete loss of power/acceleration; Vehicle unable to restart; No oil in engine (confirmed during post-failure inspection); Shaking and jerking immediately before stall
Codes mentioned: P1326 (rod bearing/knock sensor), Compression loss (cylinder #1, #3, #4 noted in narratives)
Repairs/costs cited: Engine replacement required. Estimated cost $6,000–$7,300. Many owners report warranty denial or goodwill refusal. One owner reports dealership held vehicle 4+ months without resolution. Parts shortages (e.g., catalytic converter) can delay repair 2+ years.
Recalls/TSBs owners mention: Kia consumer affairs declines goodwill engine replacement citing: (1) high mileage despite warranty periods not explicitly expired, (2) inadequate maintenance records despite documented services, (3) lack of diagnostic code (compression loss not always generated), (4) class-action settlement terms requiring rod seizure/blow-through as proof (not just bearing wear). Extended warranty disputed; some dealers state rod bearing coverage does not include compression loss or internal wear damage.
Stalling / Loss of Power at Speed (Limp Mode, No Warning)
Sudden loss of engine power and stalling while driving—especially on highways or during acceleration—often with minimal or no warning. Check engine light may appear at moment of failure or post-failure. Limp mode (restricted acceleration) reported alongside stalling.
When: Can occur at any mileage but frequently 60,000–120,000 miles; some cases as low as ~22,000 miles.
Symptoms owners cite: Abrupt stall with loss of power during driving; Check engine light illuminating at time of failure (sometimes no prior warning); Hard-to-press brake pedal after stall; Vehicle enters limp mode with reduced acceleration; Engine jerks or shudders before stalling; Hesitation or loss of acceleration despite depressing pedal
Codes mentioned: P1326 (knock sensor/rod bearing), Multiple cylinder misfire codes, Knock sensor codes
Repairs/costs cited: Diagnosis typically reveals engine seizure, rod bearing failure, compression loss, or fuel pump failure. Tow required. Engine replacement or internal rebuild needed (cost $6,000+). Some repairs refused by dealers citing warranty exclusions.
Recalls/TSBs owners mention: Kia has created tech-line cases and opened investigations in some instances (e.g., case held 128 days without resolution per narrative #18). Limp mode sometimes attributed to knock sensor or software issue; knock sensor replacement + ECU update performed in some cases, but failures recurred. No consistent remedy offered; owners report being directed to dealership in circular customer-service loop.
Engine Fire / Underhood Fire
Flames or smoke emanating from engine bay. Two narratives report fire at low mileage (~22,000 miles). Fire suppressed by occupants or bystanders; no injuries reported but clear safety hazard.
When: Reported at 22,000 miles in both cases.
Symptoms owners cite: Flames visible under vehicle or from engine bay; Smoke under hood; No warning lights prior to fire (or unspecified)
Repairs/costs cited: Vehicle towed; fire and police departments responded. Not repaired; vehicle status unknown in narratives.
Recalls/TSBs owners mention: Manufacturer notified. NHTSA investigation PE19-004 referenced by owners as documenting fire hazard risk associated with Theta II rod bearing failure and oil leaks on hot engine surfaces. No specific remedy or recall expansion mentioned in narratives.
Catalytic Converter Damage / Clogging
Catalytic converter clogging with oil carbon and deteriorating or breaking apart internally. Oil-contaminated exhaust damages converter; owner reports converter came apart and took out turbo, requiring $6,000 repair. Converter parts unavailable nationwide.
When: Develops secondary to excessive oil consumption; failure reported around 100,000+ miles.
Symptoms owners cite: Check engine light (emissions-related); Failed emissions test; Converter physically clogged or fractured (internal failure); Loss of power / hesitation
Repairs/costs cited: Converter replacement cost ~$6,000. Owner reports parts unavailable in US or Canada; dealerships placed on waiting lists. Lead time up to 2 years cited by Kia.
Recalls/TSBs owners mention: Kia advised parts were hard to come by and lead time could be up to 2 years (narrative #19). No apparent remedy or warranty coverage for converter damage caused by oil consumption defect.
Knock Sensor Code / ECU Software Issue (Recurring Limp Mode)
Check engine light with P1326 (knock sensor) code; vehicle enters limp mode. Kia's initial remedy is knock sensor replacement and ECU software update; however, failures recur weeks or months later. Root cause appears to be underlying bearing wear/oil consumption, not sensor failure.
When: Limp mode incidents reported from ~60,000 miles onward.
Symptoms owners cite: Check engine light + P1326 code; Limp mode activation; Loss of power/acceleration restricted; Loud knock noise before limp mode; Rough shifting; engine vibration; Hesitation at highway speed
Codes mentioned: P1326 (Knock Sensor Detection System / rod bearing clearance)
Repairs/costs cited: Knock sensor replacement + ECU/KSDS software update performed. Cost varies; some instances appear to be covered under warranty or recall (SC218Y3 mentioned). However, repairs do not resolve underlying issue; limp mode recurs in weeks/months.
Recalls/TSBs owners mention: Kia and dealers attribute initial occurrence to knock sensor or software and perform KSDS update. Recall campaigns SC218Y3, SC218 cite DTC P1326 and ECU update as remedy. However, multiple owners report: (1) recurrence after repair, (2) denial of recall coverage based on ownership status (used-car dealer, second owner) despite federal recall mandate, (3) refusal to perform recall due to lack of prior service history, (4) contradiction by dealers regarding whether extended warranty covers rod bearing defects.
Oil Consumption Test Delays / Incomplete Diagnosis
Dealership initiates 1,000-mile oil consumption test per TSB but fails to complete or honor results. Test repeated due to mileage overages; owners report difficulty meeting test protocol (45+ miles to dealership). Diagnostic results disputed or not provided to owner.
When: When excessive consumption reported; timing varies.
Symptoms owners cite: Excessive oil consumption confirmed by test (≥1 qt/1,000 mi); Test stopped mid-procedure due to mileage overages; Dealer unable or unwilling to complete test; No further diagnosis or repair offered after test
Repairs/costs cited: No repair completed. Test results exist but not acted upon by dealership.
Recalls/TSBs owners mention: Kia's TSB ENG 222 calls for oil consumption test; however, dealers have not completed tests or honored results per narratives. Owners cite TSB requirement and class-action settlement guidelines but dealers cite inability to complete protocol (e.g., long distance to dealership, cylinder compression loss preventing BCT test). Extended warranty terms referenced but not enforced by dealers.
Warranty Denial / Goodwill Refusal (Mileage, Maintenance, Ownership Status)
Manufacturers and dealers deny warranty coverage or goodwill engine replacement based on: (1) vehicle mileage (despite mileage not exceeding manufacturer warranty), (2) disputed maintenance records or alleged lack of routine maintenance, (3) second-owner status, (4) vehicle purchased from auction or dealership inventory. Owners report circular customer-service loops and contradictory explanations from different dealers/Kia consumer affairs.
When: Denial occurs after engine failure reported; varies by owner.
Symptoms owners cite: Engine failure confirmed by diagnostic; Owner requests warranty or goodwill repair; Denial letter citing mileage or maintenance
Repairs/costs cited: No repair performed; vehicle left unrepaired.
Recalls/TSBs owners mention: Kia consumer affairs and dealers decline goodwill engine replacement citing: (1) 'high mileage' despite warranty periods overlapping, (2) 'inadequate routine maintenance' despite owners providing service records, (3) second-owner status or auction purchase, (4) lack of diagnostic code (e.g., compression test not performed). Some owners report goodwill case opened then declined via email. Extended warranty eligibility disputed; some dealers state warranty does not cover compression loss or wear. Dealers placed customers in loops: told to contact corporate, then told only dealership can help, then denied.
Synthesized from 103 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 9 most recent
The contact owns a 2018 Kia Optima. The contact stated that while driving at an undisclosed speed, the low-pressure engine oil warning light illuminated, and the vehicle stalled. The contact stated that the vehicle jerked and almost lost motive power however, the contact depressed the accelerator pedal and continued driving. The contact stated that the failure had occurred on two occasions. The…
My engine is under the Kia class action lawsuit for the KDS with the rod bearing clearance issues. I have done all my oil changes with paper work available. I got the update to the ECU several years ago as needed to be covered. Now my engine has failed and I took to the dealer to check but they said I didn't have a specific code and that they can't do any testing to verify it would be under the…
Increased oil consumption with needing oil added and or changed half way before date or milage stated, oil changes performed by Kia dealer. Car staling and engine knocking while driving. Burnt smell while driving.
The contact owns a 2018 Kia Optima. The contact stated that while his daughter was driving at an undisclosed speed, the check engine warning light illuminated, and the vehicle went into LIMP Mode. The vehicle was towed to an independent mechanic, who related the failure to NHTSA Campaign Number: 17V224000 (Engine and Engine Cooling); however, the VIN was not included in the recall. The vehicle…
I took my vehicle to jenkins kia-ocala back in march and may of this year for my check engine light lashing on and off and acceleration issues, car shaking, and excessive oil spilling into my spark plugs. The 1st time I took my vehicle to this location i was told to "drive my vehicle until it no longer had any motor oil to "allow the motor to lock up" to then be approved to have my vehicle engine…
While driving my 2018 Kia Optima S, the car suddenly jerked, lost power, and stalled in traffic. Multiple warning lights came on at the same time including the oil light, battery light, and check engine light. I had no acceleration and the brakes became very hard to press. The vehicle had to be towed for safety reasons. The Kia dealership inspected the vehicle and confirmed internal engine…
Excessive oil consumption will burn through around 4qts of oil before 1k miles
Tl* the contact owns a 2018 Kia optima. While driving 20 MPH, the contact was notified by other motorists that flames were present under the vehicle. The vehicle was pulled over to the side of the road and smoke appeared under the hood. The contact and a pedestrian extinguished the fire. The fire and police departments were at the scene, but the contact was unsure if reports were filed. There…
I drove the car to the park about 6 miles round trip with family. I came back home and started having lunch for about 25 minutes. I then attempt to start the engine to go to my appointment but then car didn't turn on. On third attempt I had a weird noise coming out of the hood and I went back inside the house to get my gloves. When i came outside of the house, the hood of the car was in flames. I…
Had engine trouble with your 2018 Kia Optima?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the engine problem on the 2018 Kia Optima?
It's a meaningful issue. 103 complaints have been filed and the failure mode causes operational problems for owners. Repairs average $3,100.
At what mileage does the engine typically fail?
Across the 30 complaints that reported odometer mileage, most engine failures cluster between 41,000 and 102,593 miles, with the median around 77,200. A quarter of owners report trouble before 41,000; a quarter make it past 102,593. Maintenance history matters more than the odometer alone — this is the reported failure window, not a guarantee.
What does it cost to fix?
Independent shops typically charge around $3,100 for engine repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to engine?
No active recalls currently cover engine issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2018/Kia/Optima.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.