Gas in oil - Kia Optima

My 2013 Optima (2.4L GDI) has recently started getting gas in the oil. I noticed it because my oil pressure light started flickering one day, I checked the oil and the level was way above the F mark and it smelled strongly of gas. It would only happen when the oil was up to temp and I was idling, it wouldn’t flicker when I was driving.

I changed the oil and the light stopped flickering. I assumed the gas was getting past the pistons/rings (can it get into the oil any other way?), so I soaked the pistons in Berryman B12 for ~5 days. I read this had fixed the problem for someone else. The B12 would leak past the pistons slowly, some quicker than others, and some eventually stopped draining (I think, it was hard to really tell how much B12 was in each cylinder). Gas is still getting into the oil unfortunately.

I tested the PCV by putting a balloon on the end and it wouldn’t let air out the wrong way, so I think it’s still good.

What else can I test myself before I bring it to a shop for them to start tearing it apart to try to figure out what’s wrong with it?

How many miles on it? Is the check engine light on? And what codes? P1234 format please. Does it take a longer crank time to get the engine started than it used to?

At first read I’d guess you have a leaking injector.

~63K, I bought it with ~29k on it. No codes currently, it did throw P0014 a month or two ago, replacing both VVT solenoids got rid of it. It starts right up and runs perfectly as far as I can tell.

Yeah I read it could be a leaking injector. I’m wondering if there are any other easy things to look at/try before taking it to a shop, I don’t want to deal with taking off the manifold haha.

If an injector were leaking, the engine would run rough when first started until the flooded condition cleared itself.

What you might try is connect a scanner to the vehicle, and monitor the signal from the coolant temp sensor for the computer.


Even if the leak is slow enough that it doesnt really pool in the cylinder and just seeps past the piston?

What do you mean monitor the signal from the coolant temp sensor? What would that tell me? Not trying to be rude or anything, I just really don’t know haha. I’ve watched the coolant temp using my bluetooth obd adapter and app and it stays in the acceptable temp range.

If the coolant temp sensor where sending an erroneous signal to the computer saying the coolant temperature never gets above -20 degrees, the computer would stay in the open loop mode, and run a very rich fuel mixture.


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Ah yeah, makes sense. Unfortunately I dont think it’s that, the temp reads correct in the app and on the dash.

The first reason on the list for this code is dirty oil. If you replaced the VVT solenoids you got rid of the area that may be clogged and fixed the code but you may have a sludged up engine. But that might be a secondary problem.

I’m still leaning to a leaky injector… pay attention to how it starts up both when warm after a short shutdown and when cold. Does it run rough during either startup?

Ah yeah I forgot to put this in the OP (though it doesnt have anything to do with the gas in the oil, I noticed the gas before I did this) but I ran a can of EPR BG109 through the engine after soaking the pistons in B12 to maybe help clean off the pistons/rings a bit more. I’ve changed the oil probably at least every 7k miles with full synthetic so I’d be surpsied if it has sludge in it. Though the old VVT solenoids did have some black crap on the little screens… I was thinking it could had been from the previous owner maybe not changing it often enough.

Anyway… I’ve never noticed it running rough at startup, neither hot nor cold. I can drive right off and it never sputters/surges or anything, I’ll pay more attention though.

Fuel can’t get into the oil from anywhere other than past the pistons/rings, can it?

I’m guessing I should start by seeing if the fuel pressure goes down over time? Or should i check something else first? Would this work?

Where would I connect this in my car? I tried looking it up but cant find anything right now.

Thanks for the help BTW!

You have direct injection meaning the fuel injectors shoot fuel directly into the cylinders at very high pressure. Mounted in the head, not the manifold. Too high for that gauge set. The tank mounter pump brings fuel to a high pressure pump usually run off the camshaft… not sure how yours is set up… not sure there is any way to measure pressure to the direct injectors.

Ah for some reason I had it in my head that it was under 100 psi in the fuel rail and then the injectors upped the psi for some reason. I wonder if my bluetooth obd reader can monitor the fuel rail pressure and let me see if it goes down over time… I would want to just pressurize the rail and then let it sit for a while and check the pressure later?

OK, looking at RockAuto for the 2013 Optima, It shows a fuel pressure sensor so you should be able to read the pressure off the OBD2 port IF you have a reader that can access the sensor. I’d guess it is the low pressure sensor, not the high pressure at-the-injector pressure. You may be able to read the pressure, ignition ON, engine OFF to see if it bleeds down.

This, BTW is your high pressure pump… and it costs $507

Replacement injectors cost $116 each. And look like this…

Does the exhaust smell like gasoline? On a correctly running engine this could occur during the first few minutes of idling, then should quickly dissipate as the engine warms up.

The DI in your car’s name means “direct injection”. There’s could be something wrong in that system, among the possibilities a leaking injector. If the computer is injecting too much gasoline for the operating condition b/c of a faulty sensor reading , that should show up in a fuel trim test. I’m unsure if a problem with the valve timing could cause something like this. I’d guess if that were the problem the engine would run poorly, and that doesn’t seem to be the case. If there’s a problem w/the piston rings it would show up in a compression test. If the oil and filter maintenance has been consistently done on schedule, piston rings as the cause seems unlikely. Suggest next step is a compression and fuel trim test.

Misfires could contribute to this, but then the CEL would be on. I don’t see anything about the CEL above, but I presume if it were on the OP would have said so.

It’s normal for the fuel pressure to bleed down over a certain period of time.

So don’t think there’s a problem if it does.


Yeah the CEL isn’t on, I forgot to mention it but I did a compression test and all of the clyinders were between 135-140. I’ll look into what a fuel trim test is haha

Those compression numbers are on the low side, but I doubt that points conclusively to the piston rings being the cause of the gas in the oil symptom. A fuel trim test will tell your shop if the amount of fuel required to make the o2 sensor read correctly (i.e. correct fuel/air mixture) is what it thinks would be required for that operating condition. If it needs to inject more fuel to meet the mixture requirement, that a +% fuel trim. If it needs to inject less, that’s a -% fuel trim.

Everything else being equal, engines need more fuel when the coolant temp is low, less when it is high. If the problem is that your coolant temp sensor is reading a temp that is below the actual coolant temp, the engine computer would find that to obtain the correct mixture based on the O2 sensor it would have to reduce the amount of fuel based on the coolant sensor reading. In other words, a negative fuel trim. Fuel trims usually are within +/- 10%. Anything over 10% is suspicious.

Ah sxxx, I just looked at my notes, the compression test #'s were all 145-150. Does that seem more normal?

I checked what fuel info my obd reader could pull earlier and unfortunately it doesn’t look like it can get the fuel rail pressure. It looks like it can read the fuel trim though. I took screenshots of all the things I can see. The fuel trim was between -5.5 and -6.25 when I took the screenshots. This was when the car was probably completely warmed up, the coolant was definitely up to temp. Do any of the other readings look like they could be helpful?

Pics of reader data: Imgur: The magic of the Internet

I figured, I was just hoping to see if there was an excessively quick drop or something.

As the saying goes, if you hear hoof steps galloping by, think horses before you think zebras. If excessive fuel is getting into the oil, I would look for a leaking fuel injector before I’d assume piston rings or other major engine problems–especially on a low-mileage engine which has not been overheated or run low on oil.


The low compression could be explained by wear on the cylinders, pistons and rings, after being washed down with gasoline, which is a poor lubricant.

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