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GDI engines - yes or no?

So, here’s the deal. I purchased a 2015 Kia Sportage with the GDI engine (non-turbo). I did some research and primarily found that as long as you use Top Tier fuel (which I always do) this will eliminate the carbon build-up. I also had KIA run their fuel additive through my system to clean up any carbon. I currently have 7,500 miles on the vehicle. I am not digging deeper and finding out that these DI engines are having issues down the road. Has anyone experienced with with a DI engine? At least I have the 10/10 warranty.

I just wasn’t sure how (if any) improvements have been made on the DI engines. I knew there was a potential issue with the motor, but it seems like almost ever manufacture is going with them, so I took a risk with the Kia.

Last, is there anything other than Top Tier fuel I can do to prevent future issues?

Nothing. The problem is that the fuel doesn’t wash the valves, since it enters directly into the cylinder and with the valves closed. Frankly, Top Tier fuel won’t wash the valves either, so IMHO it won’t help anything. Nor would any fuel additive.

The carbon problem comes from the system that allows a bit of spent exhaust fuel to be drawn into the induction system to prevent cylinder temps from getting too high. The oxygen in the exhaust is already bound to carbon or nitrogen, so it won’t contribute to the combustion process, so letting a little in to displace a bit of oxygen tends to cool the flames. BUT, since the valves are no longer being washed by the fuel, the carbon collects on the valves.

The theory behind using Top Tier is that it’ll burn cleaner, leaving less free carbon, but the fact is that carbon and carbon dioxide and monoxide are byproducts of combustion. Can’t be avoided. I’ve yet to see any study that shows that Top Tier helps direct injection engines stay cleaner. They simply have that inherent weakness.


This weeks Motor Week - Pat Gauss had a different theory. His theory is the piston rings being used. Says that the rings aren’t constantly applying pressure to the cylinder walls and thus causing blow by. Not too sure I bilieve or really understand his theory. Never really thought much of him anyways.

Last time we had this discussion somebody had a link to a Ford (I think) engineer’s comment that they solved the problem through some design tweaks. So it seems like some cars might be less liable to have the problem. I don’t know if Kia is one of those.

But these days it’ll be very hard to avoid, anyway. I’m resigned to my next car having GDI. I hope to avoid a turbo.

I’m at 61,500 miles in my GDI Mazda 6 without any issues.

@Mike That blow-by ends up going through the PCV system and into the intake manifold. So if you drive “vigorously” and as your engine wears you will have more and more blow-by depositing stuff in the intake system.

I agree that periodic cleaning is recommended, since the purging action of gasoline washing away these deposits is absent in a GDI engine.

“I’ve yet to see any study that shows that Top Tier helps direct injection engines stay cleaner.”

Shell claims that their “nitrogen-enriched” gas has the ability to keep GDI engines clean.
It’s probably just advertising hype, but…

I have 62,000 miles on my Hyundai GDI engine (with turbo) and have had no engine issues. I do use primarily top-tier gasoline but do not use fuel additives or cleaners. I haven’t heard of any problems related to carbon build-up in these engines.

There’s are Ford and GM youtubes showing how gas flows by the intake valves when they’re open on their GDI engines. So more detergents can make a difference, it seems.

I’m sorry for my ignorance (I’m not a gear head), but will keeping the RPM’s up say when merging onto the highway help with the carbon build-up or would I be better keeping them lower in the long run?

Most of my driving is a 45 minute highway commute, so I am definitely getting up to temp which is good.

Anyway, I’m just glad I have a warranty!

Just drive the vehicle like a normal person and find something important to worry about. If this is really something you lose sleep over just trade when the warranty is up.

I don’t think it’s going to matter. Get the revs up when you need to go faster, and keep them low when you’re just cruising, just like people do anyway.

This is kind of one of those “we didn’t used to have to do this, but it’s going to become routine maintenance” things. Kinda like “we didn’t used to have to change the oil every 6 months but then we started going places in cars instead of on horseback.” :wink: As technology changes, maintenance requirements will change.

I guess in summary these engines are still too new and the empirical data too sparse to really know. Toyota uses an interesting setup in the heads used on the Toyota FRS/Madza BRZ joint project. They use both port and direct injection together, the ECU controlling the bias depending on the engine demand. Time will tell how good direct injection is on a gas engine, I guess.

I understand that newer designs run a hotter intake system to burn the exhaust gases that are recirculated, reducing the intake valve carbon build-up.


Rude? I haven’t seen a single rude comment. It’s all been just technical discussions. Why exactly did you find us rude?

Ugh, wrong forum, sorry guys! I was actually copying and pasting that to respond to someone else’s post another forum.

I appreciate all of your advice! Thanks, guys!

LOL, you mean I’m not the only one who screws up?
No problem, my friend. If that’s the biggest mistake you make you’ll have a very, very lot of catching up (with me) to do! :smiley:


“GDI engines - yes or no?”


You asked for opinions, and that’s mine

If I have a choice next time I’m car shopping, I’d rather not go GDI

I may not have a choice, because I don’t anticipate car shopping for several years, and by that time perhaps all gasoline engines will be GDI

But if I were to go new car shopping today, I would try to find something that I like, was reliable, and was not GDI

By the time I go shopping for my next car I’ll be behind the Golden Gates. I expect the dealers will all be honest and the cars all operate perfectly. And it’ll be a convertible, because the weather will always be perfect. :smile:

However, Jman, you’ve already made your purchase, so my advice would be to enjoy your new ride and focus on giving it a good wax job and learning the fun stuff about the car rather than worrying about things that probably won’t happen.

Happy motoring.

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