Poor Fuel Economy solved!? Maybe

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CX-5
So I originally posted here a while back complaining about my 2017 CX-5 having poor fuel efficiency.
Well today I think I finally solved the issue.
Long Story short, Carbon Clogged Intake Valves.

Yesterday I removed the intake manifold ( about a 20min job) and inspected my valves... GROSS.
Cleaned them with come carb cleaner and got in there as best I could. Closed it up and ran some CRC Intake valve and turbo cleaner through the engine.

Got 29mpg on a short highway trip. (Previously struggles to get 25mpg) and was able to get 29 with some spirited driving,

So if you're like me and at your whits end about MPG on your car, give the valve cleaner a shot and lmk if you see similar results down below.
 
“Everything” including regular oil/filter changes with quality synthetic oil? How about walnut-blasting the valves? This can be a DYI job, although likely a bit more involved than solvent spray.

I’m glad the OP has substantially improved his mpg and hope that continues, but I wonder about his method. The solvent and dissolved carbon and other gunk had to go somewhere, likely some into the oil and the rest against the cylinder walks and on the spark plugs on its way out the exhaust. Would that cause any damage? Don’t know, but I’d be changing my oil right after flooding the engine with stuff it shouldn't have in it.
 
I mean I agree completely,
I do regular oil changes at 7,500 miles with either Castrol Edge, or Mazda 0w-20
I've replaced air filters, brakes, both differential oils, transmission fluid and filter, and cleaned the MAF, new spark plugs, etc... was putting off taking off the manifold but it was the next step in tracking down the issue. The carbon most likely shot out the exhaust, the pistons get shot with gas, cleaning them, The issue with DI engines is that no solvent ever reaches the intake valves causing this issue.
This is a pretty common solution to this issue from what I've been reading about DI engines, and while I understand the potential risks of this I think in my case the benefits of 5mpg outweighs a soft solvent infused carbon ball getting burned and pushed out the exhaust.

I presume that due to the high compression of these engines, even minimal amounts of carbon buildup allow blow-by past the intake valves and weaken performance and cause bad MPG.

Do your own research, but I felt the need to post this since the question of BAD MPG has been plaguing me for over a year.

(Walnut blasting may be a better option, but bottom line. If you have poor MPG and can't figure it out this is a PSA to check and clean the intake valves.)
 
So I originally posted here a while back complaining about my 2017 CX-5 having poor fuel efficiency.
Well today I think I finally solved the issue.
Long Story short, Carbon Clogged Intake Valves.

Yesterday I removed the intake manifold ( about a 20min job) and inspected my valves... GROSS.
Cleaned them with come carb cleaner and got in there as best I could. Closed it up and ran some CRC Intake valve and turbo cleaner through the engine.
At 60,000 miles, it properly is a good idea to use some means to clean up the carbon deposit on intake valves. Installing a catch can helps too.
You can put a can of crc valve cleaner into the pcv/vacuum and intake before oil changes and you can minimize if not eliminate cooked oil on valves (in my skyactiv experience). I never have deposits like I see people showing online (they never did head cleaning maintenance). At most I have a film of oil which is normal.

Got 29mpg on a short highway trip. (Previously struggles to get 25mpg) and was able to get 29 with some spirited driving,

So if you're like me and at your whits end about MPG on your car, give the valve cleaner a shot and lmk if you see similar results down below.
If you see about 16% fuel economy increase after the intake valve cleaning, that’s great. But I personally would doubt most people will get this kind of fuel efficiency improvement by just cleaning up the carbon deposit on intake valves.
 
I wonder if this kind of issue is exacerbated by lots of low speed use and idling? That kind of use could be described as severe service. I wonder if using oil with the newest SAE class, SP, would help prevent deposits?

Is there an easy way to take a look, ie without removing the intake?
 
May i ask which grade of fuel you have been using? I am suspicious that some of the regular offerings are not exactly jet fuel.
I have been using premium and hate the cost but I may have drank the coolaid on the "cleans as you drive" hype. I fo know the premium has no ethanol added for what that is worth?
 
Techron is good for cleaning the injectors, right? Not necessarily the backs of the intake valves.

A number of people think Premium is worth the extra expense. I tend to agree, at least for the Skyactive.
 
Lol, true jet fuel has an octane rating below 50. Avgas on the other hand can be over 100 octane. But then I‘m not certain how “octane” is measured for avgas versus how it’s done for automotive fuel. Two entirely different regulatory bodies.

There is zero advantage to using premium fuel in an engine which is designed for 87 octane. It generally has the same detergent package as “regular” so it burns no “cleaner” nor does it prevent deposits better. I suppose that when towing uphil in very high temperatures it might reduce detonation so a bit more power is available.
 
Hmmm... I wondered that the supposed detergents in the primo help with those pesky deposits? I did have some detonation issues with my previous ride when I ran the cheap stuff and it was a DI engine.
Lol... jet fuel... also good for Fondue!
I would like to run the regular but I must be suffering from PCGSD (post crappy gas stress disorder) so I keep getting the high test....and my lawn mower loves primo too haha!
 
I get the feeling it isn't just the octane. Maybe the additives. It might depend on the particular brand or station.

I can't say that all brands of premium are better, or that all 87/84 gas is inferior. But I have had experiences that make me consider using premium most of the time. Especially ethanol-free, when I can get it.

I don't usually drive a lot of miles and the difference in price is a minor consideration.
 
I can understand where you get that feeling from. I too have tried various brands and some seem to be pretty close to that actual jet fuel octane listed earlier... some kind of watered down, barely able to ignite, used in those cool drinks with tiny umbrellas concoction that I cheerfully poured into my tank unwittingly.... performance was a little below standard shall we say?
I drive enough to want to use Regular but like I said - PCGSD hit me and then reading about coked up (diesel term there haha) valves and other bits makes me want to pay too much?
I need therapy, or maybe pursue that rocket science quick start degree program I saw advertised on my cereal box...
 
Just to be clear, there are ethanol-free fuels, but garden variety premium is e10 just like regular. Whether the additive package is better with premium is debated but most think not. Net, net, premium doesn’t buy you no-ethanol and probably doesn’t buy any increase in cleaning additives. It buys you more headroom so the engine doesn’t detune itself and make less power in challenging conditions, which probably happens very infrequently, even on the 2.5t.

- Mark
 
Thanks Mark, you may well have saved me some dough... and therapy fees haha
Ahhh, the perfect world, where we actually get informed and what we are paying for... a guy can dream at least.
 
Whatever fuel you use, the intake valves see none of it.

Octane is a burn retardant. It makes to fuel burn weaker. Sure, you can advance timing, but in these engines I'd never run anything above 87. They all feel slower with premium Subjective, I know.
 
Believe me, the turbo 2.5 feels much stronger running 91 versus 87 - I’ve tried it several times. But if you never explore the engine above half-throttle then it probably won’t be noticeable.
 
Believe me, the turbo 2.5 feels much stronger running 91 versus 87 - I’ve tried it several times. But if you never explore the engine above half-throttle then it probably won’t be noticeable.
Only if you rev the 2.5T above 4,000 rpm.

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