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GDI Engine Question

Hi all!

I just purchased a 2015 KIA Sportage with the 2.4L GDI engine. Anyway, I have been dong some research on the this type of engine, and it appears that it suffers a lot from carbon deposits. Kia recommends their additive if top tier gasoline is not used. I have been using Shell, but I was wondering if this type of engine will be a real headache down the road? Is there anything in addition to the KIA manual that would help keep the carbon deposits low?

I have read that Audi and VW have had tons of issues with this engine, and some people were reporting their engines blowing up. I’m just wondering if any of you have GDI engines, and how reliable they’ve been?

Besides fuel, sure to use the exact oil Kia recommends. Certain oil additives can help prevent or at least reduce carbon deposits from forming.

It’s simple.

A Gasoline Direct Injection system doesn’t expose the intake valves to the detergents in the fuel to keep the valves clean.

And because the EGR/PCV gasses are introduced into the intake system for emission control, deposits can form on the intake valves.

It’s everywhere on the web if you want to look it up?


Your car has a really good warranty, just follow the service schedule and if you have any concerns just talk to the service department where you purchased the car. You are either worrying way to much or you have buyers remorse.

This vdo might be helpful

I questioned Tester on this same issue in another thread, and after spending some “thought time” digesting his response I agree with him. I had read that direct injection engines were prone to carbon buildup problems, but not exactly where. Tester’s explanation makes perfect sense.

IMHO unrealistic federal CAFE and emissions requirements are forcing manufacturers to take huge risks with unproven technologies, and direct injection engines and continuously variable transmissions are two for which buyers seem to be paying an awful price.

I’ve put these two “features” on my list of things that I’m not willing to accept on a new car I might buy. At least not until they evolve to being as reliable in the long term as are port injection and traditional automatic trannys.

You’ve already made your purchase, so all I can do is suggest that you follow the manufacturers recommendations fully. Sincere best.

@GeorgeSanJose: Great video. Thank you.

One (costly) solution would be a second set of fuel injectors.
Traditional port injectors aimed at the valves.
They’d inject only enough fuel to establish a lean baseline (say >20:1 AFR).
Hopefully that would be enough to keep the valves clean.
The direct injectors do the rest and still have most of their advantage from injection timing.
It would lose the possibility of fuel free scavenging during the valve overlap period.

Toyota/Subaru have dual injectors on the FR-S/BR-Z twins. One direct, the other in the intake manifold. Only one I know of that does it.

Seems like just about all makers are going to direct injection. Another problem with it is increased particulates emissions, similar to a diesel.

I read about the Toyota/Subie engine. Apparently the pulsewidth of each injector (port vs. direct) is balanced based on what will provide optimal performance. Personally, I’d rather wait a few years until the bugs are worked out.

Yup… @texases nailed with that comment. Subaru/Toy have that contingency handled.

Carbon buildup has been the least of my problems with my 2013 Equinox with a 2.4 Ecotec DI. The pistons, rings and timing chain were replaced at 42k miles. This engine had a issue with excessive piston ring wear leading to increase oil consumption.

I used Seafoam spray to clean the intake at 25 and 35k miles. The mechanic did not mention any carbon buildup after the rebuild. There is a risk of engine damage if not done carefully.

I wouldn’t worry about Volkswagen or Chevrolet, each manufacturer seems to be have teething problems with direct injection. I would search Kia forums to see if there are any known issues with your particular engine.

In my experience DI seem to be very hard on oil. I was doing 5k, then 4.5k oil change intervals after 20k when the oil consumption started on my Equinox. I’m going back to a 4k change interval from now on.

I would recommend:

  1. Check your oil level on a regular basis
  2. Don’t stretch out the oil change intervals, at least go by the “Severe Service” maintenance schedule.


Yes, that video was very instructive, and it mentioned the walnut shell scrub that some Mini owners have talked about in this forum. That leads me to a question which may–perhaps–be overly naïve or uninformed, but…Given the abrasive nature of ground walnut shells, what is going to happen to the cylinder walls if any bits of shells aren’t vacuumed out? Certainly nothing good is going to result from those abrasive particles.

Is something like a MotorVac used to remove the ground walnut shells from the cylinders after they have done their work on the valves, or…do they actually remove all of the valves in order to do the walnut shell scrub?
If it is the latter, the labor costs must be…high…for this cleaning procedure.

This article is very informative.


If I understand this correctly:

  1. The use of top tier gas or fuel cleaning additives has no effect on reducing the buildup of carbon on the intake valves in DI engines.

  2. The buildup of carbon on the exhaust valves in DI engines is no different than in the prior port injection engines.

Does anyone see it differently? If so, please explain.

It may all come down to temperature… In a DI engine…the intake valve is NOT wet with fuel prior to compression and ignition. In DI…the valve probably heats up to near exhaust valve temps as it is not “quenched” from behind with fuel and air charge from behind… This is just my theory however.

Also since this cooling down and washing off of the intake valve is not taking place…perhaps carbon adheres to it more readily? The airflow pattern may also play a part…the exhaust valves larges surface area is facing head on into the very high velocity of escaping exhaust gasses…something that in my mind would help it to stay cleaner…than that poor intake valve that has the reverse airflow occuring. Its difficult if not impossible to “blow Off” carbon deposits if they exist…when the airflow is from Behind the valve…that would do nothing to scour the intake valves surface facing the piston.

Just my thoughts…no research involved. Hold Water?


Well, the intake valve is cooled with air, just not with fuel. So you’re right, it’ll be hotter, but not nearly as hot as the exhaust valve.

True…definitely Hotter… How hot? The engineers know…but think about it…the intake is being skipped of that cooling and is now basically a heated surface for combustion… It wouldn’t surprise me too much to learn that it somehow got hotter than the exhaust. Might be one of those things you say to yourself…“Man I would have never thought” I would accept any logical assessment at this point…but this line of thought might be the key to it all.

But isnt hotter better for no carbon to build? Or is it worse…or is the actual temp rife for carbon to build. Some engine designer somewhere definitely knows the answer…thats for sure…but I am not one of those individuals and dont have their monitoring capabilities by a long shot…thats expensive stuff right there…

The world may never know. Kinda like the Tootsie Pop Question…


? but the intake valve has cool air flowing by it every intake stroke, never hot air/exhaust flowing by it, unlike the exhaust valve. The only difference is the absence of fuel.