Turbo and Direct Injection
 

My new WRX (which i absolutely love) has direct injection.

Apart from the well documented BMW and Audi (go figure :rolleyes:) direct injection issues with carboned up intake valves, what other cars do you have experience with that have had to have the intake valves cleaned regularly / periodically?

Most of my driving is at highway speed with the engine at 2700 RPM.

Will highway driving accelerate or alleviate this issue?

There are a few aftermarket 'fixes' available such as oil catch cans, water / meth injection, EGR delete but I don't want to interfere with my warranty to fix a problem that I may not encounter.

One item that reduces liquid oil in the intake tract / combustion chamber is an aftermarket oil liquid / vapor separator. It is installed in series with your vacuum side PCV. All modern engines have very low friction - tension piston rings, especially the oil rings which create the most drag.

The benefit is low rotational friction loss - improved power / mileage and performance. Down side is when you run them hard they will push liquid oil into the PCV system. Look into that for your specific application.

Also cheap / non branded / gasoline has less additives to prevent this. My experience - use a top tier brand like Shell gasoline. Take that part out of the equation.

Something I cant understand is how fuel brand could make a difference. With direct injection, the fuel is injected into the combustion chamber directly so it never sees the back of the intake valve like it would in a port injection engine.

I've seen comments like this elsewhere and don't understand the logic. I'm not saying its wrong.

I'm baffled by this too unclebilly (backside of valves never see the gas). I do know that Honda CR-V turbo's have been experiencing gas in the oil to a certain extent, with some reporting the oil is way over full when they check their level.

There are a lot of good oil separators on the market, as Asphaltgambler said above, google to find a good one for your application. For me, its cheap insurance.

Also, I'd thought the Subaru DI engines also used secondary port injection in part to wash the valves.
https://www.caranddriver.com/news/explained-why-some-engines-have-both-port-and-direct-injection
https://oppositelock.kinja.com/state-of-the-flat-4-us-my2017-1794660042

Maybe just the BRZ ??

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This came up on another forum. Some companies seem to have the bugs worked out on their DI engines. Many do not.

I think it is oil vapour from the PCV or oil separator that enters into the intake system and then ends up on the valves. I just removed the intake manifold from the BMW e60 (not direct inj) and was surprised how much oil film was in there, it uses a oil separator and they often fail. The intake valves looked fairly clean probably from the fuel constantly washing them.

Egr
exhaust gas recirculation

Just about all modern engines are now direct injected. Very few experience any sort of carbon buildup. This was super common on early DI engines but is mostly a non-issue by this point. If you have a nearly new WRX you should be fine.

Your highway driving with a properly warmed up engine will be a plus in many ways including the health of your intake. I have a 2009 BMW E61 that has the twin turbo N54 engine in it. I use a catch can and periodically run an FI cleaner/additive like BK or Motul. It seems to help.

There are by- products of combustion from fuel that will make its way to your oil. Cheap branded gas will over time leave by- products in your oil - which will make its way into the PCV system.

Also most production turbo's will seep small amounts of pressurized engine oil into the intake tract.