Currently have 72K on my 15 nx F-Sport... Yeah I drive a lot, I know. I started noticing my range getting lower and lower and noticed I was filling up more often. When I first got my NX 4 years ago I had a range of 330 to 340 miles on a full tank. I averaged anywhere from 23 to 24 MPG with about 50/50 city/hwy driving. I replaced the original spark plugs with OEM ones a couple of thousand miles ago and this had made no improvement at all. All my tires are inflated to 35, no check engine light, car runs perfectly fine, and my K&N air filter is nice and clean. Any thoughts where else I can check ? Is the engine just "wearing out" and not being as efficient as before? I filled up this morning and my range was at 297 miles. I've always used premium gas and kept up with full synthetic oil changes every 10K. I drive like an old man and my car rarely touches 4K on the rev meter... What gives?

 

welcome to the world of carbon build up , intake valve cleaning and what not. Common on most turbo engines at around 60k miles... When it gets really bad where you start having misfires you will take to dealer and get it fixed. Please let us know how much it cost when you get to that stage.

 

Carbon build up? But Toyota made it build up proof, right?
I'm just being sarcastic. gulshan has good point. It's called walnut shell blasting. I think, it's somewhere around $600 or so. They remove intake manifold and inspect intake valves for build up. If there is enough, they blast it with crushed shells.
Welcome to the world of GDI engines. Turbo has none to it. It's the direct injection that does this.

 

you have to drive these carbon prone buildup engines hard. a redline a day keeps the mechanic away.

 

 

So essentially I have to drive this card hard to prevent carbon buildup? What about any fuel treatment/additive? I've heard good things about Lucas products.

 

All top tier gas like costco is loaded with fuel treatment additives. This build up happens in spite of that. If you add more techron or whatever they may just provide some temporary placebo affect where you feel it pulls harder now like when you put on some aftermarket air filter. I would just wait till either mileage gets really bad or you have cold start misfires. Hear the engine on cold starts. A rough idle is another tell tale sign..that it is time for carbon cleanup.

 

Haha, great video, thanks for reintroducing me to Scotty...what a hoot, and he's a good teacher too.

True story: My mother-in-law, known for her lead foot, was pulled-over by a motorcycle policeman a few years back and explained the reason she was speeding on a city street was to "clean out the carbon" in her Camry's engine. Apparently the officer laughed and advised her do her "carbon cleaning" on the highway next time, and let her off with a warning.

 

Nope. Won't do squat to clean valves.
reason being, in GDI engine, as you have it, petrol is injected directly into the combustion chamber. In conventional engine, petrol is injected into the intake manifold, mixed with air stream, and only THEN reaches combustion chamber.
Main difference is that in conventional engine, air fuel mix is flushing intake valves, as it goes past them. thus, it cleans valve heads and valve seats.
In GDI engine, this does not happen. Hence, with every cycle, small amounts of exhaust escape through intake valves, thus creating build up on them.
Toyota is aware of this and added 2nd set of injectors into the intake manifold. With exactly that purpose - to keep intake valves clean. But they engage only at very high RPMs.
So yeah, you should race your car from day one, to keep valves clean - or, end with them slowly functioning worse and worse. When build up is there, petrol will not flush it off anymore.

 

if your nx has sport mode, I would use that for a week or more and see if it helps.

 

This car has both direct and port fuel injection, so it shouldn't have carbon buildup problems like other direct injection engines.

 

I'll quote myself;

Toyota is aware of this and added 2nd set of injectors into the intake manifold. With exactly that purpose - to keep intake valves clean. But they engage only at very high RPMs.

So if you drove like grandma, pursuing gas savings on expensive premium gas - you didn't really engage port injectors=buildup.

What I am trying to say, port injectors are not running all the time. they are auxiliary injectors engaged only during high fuel demand.

 

First thing I would do is get rid of the K&N filter and see if your mileage improve. Those things let thru too much dirt when clean and become too restrictive when dirty. lexus do not have carbon build up problem usually due to the dual port/ direct injection, its very unlikely to have carbon build at 50000 miles in a car with dual injection, something else might be causing this.

 

According to this https://www.caranddriver.com/news/a1...ect-injection/ both port and direct injection are used during low to medium engine load and rpm.

 

Interesting, thanks for sharing.