Has anyone had any carbon build up issues on the intake valves yet???

 

No, am I supposed to? I think there was one person who reported it a while back, but forget who.

 

This question as it pertains to Direct Injection engines has been bugging me recently. (I OBVIOUSLY have too much time on my hands, LOL)

In many manufacturer's engines, carbon buildup on valves has been an issue. (I'm talking about Audis and Hyundais...)

Often, the manufacturers recommend Top-Tier (extra detergent) gasoline for their DI engines. But I cannot understand how this would make a significant difference, as the fuel is squirted into the combustion chambers directly, AFTER the intake valves.

++++++++++++++++++++

Decades ago, I would squirt water into the intake of some of my cars to remove carbon deposits (and eliminate pinging). If I owned a DI equipped car, would this practice be beneficial?

 

I wonder if not enough miles have been put on these engines yet to see the problem. From what I'm hearing it's inevitable at some point and top tier gas only delays it.

I know Mazda says they put an oil/air separator in their EGR system to supposedly eliminate the problem.

 

Or... Maybe it's not a serious problem?

There's plenty of people who have a lot of miles on their GK's. I suspect most of the valve coking issues are related to the fuel source moreso than a design issue.

I know there's people who have posted up high mileage on their cars; have weighed in their experiences, or are you just focused on the few who have commented on their isolated valve problems?

 

As I understand it, the crankcase vents into the intake air box where oil mist from the crankcase then collects. That's been standard procedure on cars for a long time (aka PCV, or positive crankcase ventilation). If you have a drain hose or other system to get rid of that collected oil, the air drawn into the engine for combustion won't have any oil mist in it.

But if the oil that's collected in the air box is just sucked back into the engine during combustion, you will have an oil film collect on the back of the intake valves. With a conventional engine the incoming air/fuel mix will "rinse" that oil off the intake valves, but in a direct injection engine the fuel is injected after the intake valves so there's nothing to "rinse" the accumulated oil mist off the intake valves.

Thus the oil eventually becomes baked into the back of the intakes valves and that's how you end up with carbon deposits. Because no fuel hits the back of the intake valves in a DI engine, nothing in the fuel (additives, cleaners, etc.) can help clean the back of the intake valves.

The solution some people favor is to install a mod in the intake air box so that the oil is collected in a drain container and thus is not drawn into the engine during combustion. This obviously requires that the drain container be periodically emptied of the collected oil.

 

If there are lots of people with 50-75k miles without an issue that's good news, I just haven't heard from very many.

 

Wouldn't an issue like that be covered under the 80,000 mile emmissions warranty?

 

Only if it throws an emissions code. If it just runs crappy or gas mileage goes down, too bad . . .

And I'd sort of like the car to last beyond 80K miles. Or I would have bought something from GM or Fiat Chrysler.

 

I don't think it's an engine killer, it would just be costly to take the intake off and blast the carbon off with walnut shells which is what most people are doing.

 

The other issue that you have is that since the fuel is injected directly into the cylinder, there is no fuel at idle washing the oil from the valve guides off the valve.

 

No, not an engine killer. But the potential cost and annoyance of doing that is absurd, considering that I have never done that with any vehicle at much higher mileages.

I'll wait and see. My wife usually gives her cars away to relatives when they are several years old, with much less than 80K miles. So probably not an issue for me.

 

People on the Colorado forum are having problems with intake valve carbon / coking on the 3.5 DI engine at much lower mileages than you are asking about. Many of them are installing an oil separator which they call a "catch can". Ethanol diluted "top tier" fuel will not help in this situation because the fuel is injected into the system past the intake valves.

 

Valve "Coking" (SP?) is a long time issue with non turbo diesel engines as well.
I know we used to pop tractor heads off each season and clean them. But thats been
like 30 years ago..