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.... other than the rabbit's foot carried in the glove box in the hopes of avoiding the Theta II affliction.
Is it the OEM rabbit's foot that Hyundai/Kia gives free to all Theta owners, or did the original one get replaced under extended warranty after it went into limp mode?
 

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I have removed heads, soaked the inlet valves in situ (sometimes for a few days) in a variety of solvents, and nothing removed the deposits. The caveat is that all those heads had at least 70k miles on them and the deposits were well established and possibly 'baked' on by hundreds of hours of running time.

One of the chemicals used was CRC and it didn't touch a thing. I don't dispute their claims though, but believe the usage regimen must be initiated early in the engine life and implemented as recommended and consistently to affect deposits.

Mechanical removal of the valve deposits is problematic. I wouldn't be comfortable applying a rotary wire wheel/brush to valve stems and seats, though I can't state categorically that it would damage them. I've had valves out of a head but more to examine them for wear or erosion and have attempted to mechanically remove deposits from a few, to little avail. I'm not sure if Hyundai uses a coating on them or not ( I suppose I could always buy a new one to inspect :) ).

My final observation is that the impingement and adhesion is at most marginally affective to the valves, but recirculation of hardened particles thoughout the engine could have deleterious effects, which may be a rationale of the the catch-can.
About the best approach I've see is to do walnut blasting (properly!) with the intake valves in the closed position. You can get a special shop vac nozzle (BMW folks have used such a thing) to make this much less of a mess. HF sells many inexpensive items that could make a good "kit" for doing this manual method.
 

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About the best approach I've see is to do walnut blasting (properly!) with the intake valves in the closed position. You can get a special shop vac nozzle (BMW folks have used such a thing) to make this much less of a mess. HF sells many inexpensive items that could make a good "kit" for doing this manual method.
That's interesting since one might perform this without removing the head. The intake camshaft would have to be loosened off sufficiently to permit valve closure and intake manifold would have to be removed. Blasting media though would have to be guaranteed completely removed.
 

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That's interesting since one might perform this without removing the head. The intake camshaft would have to be loosened off sufficiently to permit valve closure and intake manifold would have to be removed. Blasting media though would have to be guaranteed completely removed.
Normally, one would just rotate the crankshaft with a big socket to get the cylinder you want to clean's intake valves to fully close. It does involve removing the intake manifold and covering up the exposed other intake ports cause even with a vac, the walnut dust does "go everywhere", at least lightly. There are various videos online that show the basics of doing this on various cars. Was considering doing this to mine until I got the "Rod knock of death" and got my long-block replacement under warranty at the Kia dealership.

This picture is showing the worst cylinder (#2) on my old engine after the swap:
443306
 

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Normally, one would just rotate the crankshaft with a big socket to get the cylinder you want to clean's intake valves to fully close. It does involve removing the intake manifold and covering up the exposed other intake ports cause even with a vac, the walnut dust does "go everywhere", at least lightly. There are various videos online that show the basics of doing this on various cars. Was considering doing this to mine until I got the "Rod knock of death" and got my long-block replacement under warranty at the Kia dealership.

This picture is showing the worst cylinder (#2) on my old engine after the swap:
View attachment 443306
Wow, never saw one that bad, not even close!
 

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You seem to take very good care of your car and yet the issue still occurs. Man, it's like a roll of the dice. Is Hyundai worth it?
Thats exactly what I been thinking with hyunfai its a roll of the dice. I too am facing very bad gas milage amoung other issues with a car I just bought with 90% loan left to pay. Will never buy another hyundai again. Back to Toyota and Honda.
 

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Will never buy another hyundai again. Back to Toyota and Honda.
I drove Honda's for years from the late 80's - 2000's they were very dependable vehicles literly bullet proof with there multiport fuel injection system. until Honda decided to go direct injection - GDI on the hole model line-up its proving to be troublesome.? it gets better they joyned GM to build electric vehicles. What.! ? not the brightest decision if you ask me. soory honda no more. i would look strongly at "Toyota" - there ahead of the game right now.

www.hondaproblems.com/oil-dilution/
 

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Will never buy another hyundai again
Well, Honda has struggled with turbo engines that dilute the oil with fuel; and Toyota still make engines that gunk up the oil control rings and consume excess oil.
All the car makers struggle to meet rising fuel efficiency standards as vehicle weight rises to meet rising safety standards.
It's similar to the struggles to meet emission standards in the '70s before there were computer controls and fuel injection.

My previous car was a Toyota and four Hondas before that.
 

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Agree... manufacturer name preferences should not apply here. One of the most troublesome engines is the Honda 1.5. Toyota makes GDIs also.

When searching new vehhicles, pay attention to the engine specs. I regretted buying my Santa Fe GDI months after purchase. So when the wife wanted a new ride, I chose South Korea-make again. But this time we bought the Kia Soul 2.0 MPI engine.
So we can have our cake and eat it too - by purchasing MPI over GDI / TGDI engines.

Or, we can just take care of our GDIs better and keep them.
Run top-tier fuels
Run non-ethanol fuels.
Run mid-grade 89 octane fuels
Use SP / Dexos 1 Gen2/3 oils in 5w30 grade and not 5w20.
Change your oil at severe service intervals of 3.75k.
Use CRC GDI Intake Valve Spray every 10k
Use 12-20oz Techron Fuel Cleaner in your gas tank right before every 3.75k oil change.

Do not baby that GDI engine Open it up / hammer the gas pedal a few times on freeway drives. If you only drive city, take it to the freeway for a 10 minute drive on Sundays. Blow the carbon / soot out of the exhaust once in a while.
 
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Do not baby that GDI engine Open it up / hammer the gas pedal a few times on freeway drives. If you only drive city, take it to the freeway for a 10 minute drive on Sundays. Blow the carbon / soot out of the exhaust once in a while.
Your absolutly right about that.! the S.F. makes a lot of carbon in a hurry. wife drives the S.F. very conservatively but when i get in it and drive it with the engine fully warmed up i stomp it & look back in my rear view mirror & notice light black mist of smoke coming out in the rear. 2nd stomp almost gone 3rd stomp all gone. highly recommend the italian tune-up be done to it every now and again. LOL (y)
 

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Your absolutly right about that.! the S.F. makes a lot of carbon in a hurry. wife drives the S.F. very conservatively but when i get in it and drive it with the engine fully warmed up i stomp it & look back in my rear view mirror & notice light black mist of smoke coming out in the rear. 2nd stomp almost gone 3rd stomp all gone. highly recommend the italian tune-up be done to it every now and again. LOL (y)
That's probably just releasing crud trapped in the combustion chamber or exhaust catalytic convertor? I doubt it's cleaning the valve chamber or piston heads.
 

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That's probably just releasing crud trapped in the combustion chamber or exhaust catalytic convertor? I doubt it's cleaning the valve chamber or piston heads.
Its doubtful that will remove any carbon from the intake valves which is the problem area.
Use an GDI intake cleaner as preventive maintenance . Unless you pull it apart and walnut blast or scope it you never really know if you have carbon buildup but it is a problem with all GDI and its cheap preventive maintenance and IMO worth the $ 10-15 every 20-30,000 miles
 

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That's probably just releasing crud trapped in the combustion chamber or exhaust catalytic convertor? I doubt it's cleaning the valve chamber or piston heads.
My original reply was not a cure. What I suggest lessens the buildup & carnage. It possibly doubles the delay-time of more thorough maintenance that's eventually needed.

If you are looking for a backyard, amateur mechanic cure, then don't buy TGDI / GDIs and invest in a MPI engine. That's what I did when we shopped a 2nd new vehicle for the wife.....ie.... Kia Soul X-Line 2.0MPI..
 

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Its doubtful that will remove any carbon from the intake valves which is the problem area.
Use an GDI intake cleaner as preventive maintenance . Unless you pull it apart and walnut blast or scope it you never really know if you have carbon buildup but it is a problem with all GDI and its cheap preventive maintenance and IMO worth the $ 10-15 every 20-30,000 miles
I feel like the intake cleaner defeats the purpose as you're releasing this built up carbon gunk and the chemical spray back into the environment, provided it makes it through the engine and exhaust which is also a concern. Walnut blasting is good since all the carbon can be hoovered up and safely disposed.

What I find odd is the manufacturers lack of transparancy about it, we owners need clear instructions from them on how to maintain our engines. The synical side of me thinks they only care the car works for up to 50k miles, after that they can just blame problems on previous owners/independant garages.
 

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That's probably just releasing crud trapped in the combustion chamber or exhaust catalytic convertor? I doubt it's cleaning the valve chamber or piston heads.
Your right about that, i rather see it going out the tail pipe than staying in the engine. lol i talked to a German mechanic before he said in his Country Frankfurt Germany to get rid of carbon on his VW he puts his vehicle up on a hoist and Taps all around his exhaust & manifold area using a ball peen hammer to loosen up carbon inside exhaust system then adds some liqui moly fuel cleaner to tank and does 20 minutes of high speed driving on the Autobhan. 🤔 gotta like those German's!! :)(y)
 
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