Consider a PCV catch can with a DI engine. Without fuel hitting the back of the valve, carbon build up can be more likely. It isn't necessarily an issue, but it's cheap insurance and helps all engines keep clean.
Great article bowtieguy and I sent it off to Miro at Synlube to see what he thinks will happen if instead of Dino oil in the engine we used his Synlube which should not form those deposits. This looks like the purpose for the nitrogen enriched shell gasoline, acetone may also play a role in this area and it may also explain why my xB engine still screams like a raped ape when I nail it at 48k miles . . . No valve deposits due to Synlube and acetone use.
Well that doesn't seem to be the issue as much as the direct injection gasoline is getting into the crankcase oil (Synlube) at as much as 2% contamination from the oil samples he has tested. I guess there is something to be said to letting it evaporate a little before it enters the cylinder.
Many automakers’ gasoline DI engines do not appear to exhibit any carbon build-up issues at all, however. (ed: note the brands with problems in the article)
Stephen Russ, technical leader for combustion for Ford’s 2-liter Duratec DI engine, said that similar to GM, engineers have determined the proper injection-timing calibration to help eliminate the carbon deposits. But Russ also said the technology of injection components – particularly the high-pressure solenoid injectors – has quickly matured, meaning excess valve deposits in most DI engines should become a thing of the past as these improved components are incorporated into production.
...the rapid adoption of DI has actually illuminated an issue, not caused one. A “dirty” intake or exhaust-recirculation design can easily go undetected in a conventional port-injected engine due to the cleaning effect of gasoline passing over the intake valves. When the same engine designs are adapted to direct-injection fueling, however, that cleaning effect is suddenly lost – and the carbon layers can build.
Along with getting the right valve timing down, manufacturers are also cleaning up the EGR and PCV emissions before they get into the intake. Toyota has a hybrid port/direct injection on some engines so fuel washes off the valves part of the time.
It appears they have done their home work or learned their lessons with DI engines, and carbon build up should be less of an issue. I wouldn't worry about getting a car with DI. I would prioritize installing a PCV catch can, but then the simple one on the Ranger, w/o DI, was catching about tablespoon of oil each week.
I know this is an oldish thread but I stopped posting here after I bought my Fit and didn't have to worry about FE anymore. I just traded mine off on a new Civic. I learned about a year after I bought my Fit in 2009 that the Civic is a much better car when I rented one on a trip. They just don't compare. The only thing the Fit has going for it is lower price (barely) and the cargo space (which I do love). But it was such a slow, buzzy little thing that I just couldn't take it. A rock took out my a/c condenser (frequent Fit occurrence) and I used it as an excuse to get a Civic Si. I don't care what anyone says about the 2012 Civic. Commute for 2+ hours a day and you will be crazy not to pick the Civic for any reason, including FE. After 2 years, I could barely keep my mileage in the mid 30s, even though I do 99% highway at or below the speed limit. So far in the civic (and this is w/ a 2.4l), I can make a few trips up to vtec happy land in a tank and still stay in the mid 30's without even trying.
Sorry, rant over...I just feel like I just got out of jail.
I have had 3 Civic Si's over the years. I could get as high as 39 mpg out of my 2008 with the 2.0L and short gearing. It was an excellent driver's car. Still, I prefer our 2010 Fit. Its engine is a little coarse at higher RPM, but we rarely drive it above 70 mph anyway. It is a great hauler, and I like the interior, dash, and gauges much better than the Civic's (that includes the 2012, which I have driven and liked much less than the previous generation's).
We have been driving our Fit for 2 trouble-free years. I am averaging 44 mpg on the current tank, and I typically get over 40 mpg when I drive it. It is nearly as quick as my 2005 Civic Si (8.3 seconds to 60 versus 8.0). My wife and I like the exterior styling better than the Civic.
As far as the rock taking out the A/C condenser: Any vehicle with a low nose can have this happen. I've never heard of it happening in a Fit. I have seen this happen on my neighbor's 2005 Civic Sedan, though.
To say that someone would be crazy not to choose the Civic over the Fit or any other vehicle is kind of insulting. I am not crazy. The Fit fits my needs just fine. Sure, I like the Civic. I've owned 6 of them, including 3 Si's. But please recognize that different people have different needs and preferences. This forum is not the place for close-mindedness.
I'm giving my opinion, that's what the internet is for. I bought my Fit thinking I had to get something similar to get high FE out of a non-hybrid or non-diesel car on the highway. I was wrong. It does fit the "cheap small car" criteria. I just don't think it's the best option for long daily highway commutes. It's jerky steering , interior noise, and aerodynamic drag let it down.
Re the condenser issue, here's one of many threads from fitfreak: http://www.fitfreak.net/forums/2nd-g...ight=condenser
I realize it's not a unique problem. But it happens with a high enough frequency to Fits that there's a cottage industry of folks on eBay selling gutter mesh and other types of screening materials precut to serve as additional protection on the Fit.