Carbon buildup and octane rating

[Falcon_LS]

This is a weird one. My Explorer was initially my boss's car and was bought at the same time as another Explorer for one of our managers in November '10.

Mine has almost 23,000 miles on the clock, the other has 17,000 miles - both 2010s. Now, mine has always run on Euro II rated 91 RON (87 AKI), whilst the other one has always run on Euro II rated 95 RON (91 AKI). The insides of my tailpipe are as clean as a whistle, whilst the other one's got hard carbon build up inside the tailpipe. The surrounding of the tailpipe on the other vehicle is also caked in black carbon. There's also soft carbon in there as well - if you take a piece of tissue paper, you can wipe it right off, but the hard carbon remains stuck to the metal.

Sure, I've run CRC Fuel Injector Cleaner and Liqui Moly Fuel Injection Cleaner a few times, but I'm not sure just how much of a difference that would make.

Could the carbon build up be linked into the octane rating, using a higher octane than recommended, or the quality of the gas being used?

 

[widman]

Carbon will build up with poor combustion, short trips, etc. To a certain extent it is "normal". That is why products like Techron can show improvement. I'd say he probably does shorter drives.

 

[yonyon]

Are the usage conditions the same? I've found that while my boss's cars tend to go through replacement parts such as engines, batteries and such, mine tend to eat little plastic retainer clips and things like that almost as fast.

 

[Falcon_LS]

I drive mine all over the place, whilst his drive mostly consists of a 24 mile round trip to work on weekdays and one or two 20-30 minute highway trips over the weekend. I spend more time idling in bumper to bumper traffic though.

 

[RiceCake]

Buy two used cars of the same year, age, and mileage and try to compare the two. The differences are probably entirely down to how he drives it. Octane won't have any effect on that.

 

[Donald]

What do the owners manuals say about octane? 87 or 91 preferred or 91 required?

Unless it says 91 required the antiknock sensor will deal with any octane between 87 and 91.

Not sure about Kuwait, but if it says 87 octane is it really that octane? In the US I believe they are snot on.

 

[morris]

MMO

 

[crazyoildude]

higher octane usually means more carbon. I have seen it many times

 

[Clevy]

Originally Posted By: crazyoildude
higher octane usually means more carbon. I have seen it many times

Ditto. More octane equals harder to burn and can lend to incomplete burn. Could be why there is more detergent in premium?

 

[Kuato]

I read an article many years ago, that using a higher octane than specified would cause carbon fouling over time. Sorry I can't find the article; but the basics were that the higher the octane, the more resistant to burning (insert long technical discussion about octane here, or search for it on BITOG) so that when using higher than specified there would be more soot (carbon) generated.

This research was done after I bought a car from my brother. It was spec'd for 87 and he always put in 93. The car would knock terribly on 87.

After reading the article, I started by using half 93 and half 89. Did this for about 5 tanks of gas, then moved to 89 for 5 tanks, then 50/50 89 and 87 the finally back to 87. Also used plenty of fuel injector cleaner during this process.

The upshot of all this is that when I moved down in octane, there would be some knocking (especially under heavy acceleration ) which would gradually go away in the 5 tanks. Once the process was complete, it would run fine on 87 with no knocking...all the carbon had been burned off.

 

[TFB1]

Agreed^^^^^

Basically if the engine doesn't have the compression to make the higher octane necessary, it's not burning as cleanly and will carbon up over time...

 

[mechtech2]

Are there cats on the cars?
Are the O2 sensors identical in their sensing?
Are the pipes the same [material and diameter]?
Very importantly, are the cars driven identically?
How about thermostat variances, and the cooling systems?
Variance or faulty EGR systems?
Who knows what fuel you really get there?
Variance in valve timing?
And on and on...

As to high octane leaving more deposits, remember that we are not using leaded fuel. [old gas had lead, and more in high octane - deposits could be different] Nowadays, forget about it.

High octane is more resistant to 'lighting off', but once initiated, it burns completely - it's 'off to the races'. [there may be a few nano seconds difference in burn rate]

I have never seen a difference in cyl head deposits with regular or high octane being the factor.

 

[spackard]

Originally Posted By: Falcon_LS
The insides of my tailpipe are as clean as a whistle, whilst the other one's got hard carbon build up inside the tailpipe. The surrounding of the tailpipe on the other vehicle is also caked in black carbon. There's also soft carbon in there as well - if you take a piece of tissue paper, you can wipe it right off, but the hard carbon remains stuck to the metal.


Wierd to see black in such a low mileage.
Just saying, on my high mileage car, I got rid of the black carbon buildup at the tailpipe via propane torch. It comes back though, and grows from the very end of the tailpipe, inward. That figures; as the pressure drops the carbon falls out of suspension and deposits on the metal. So, the worst part of it is the piece you see. A few inches in from the tailpipe is much cleaner. I imagine the closer to the exhaust ports the cleaner it is.

 

[Doog]

Originally Posted By: Falcon_LS
This is a weird one. My Explorer was initially my boss's car and was bought at the same time as another Explorer for one of our managers in November '10.

Mine has almost 23,000 miles on the clock, the other has 17,000 miles - both 2010s. Now, mine has always run on Euro II rated 91 RON (87 AKI), whilst the other one has always run on Euro II rated 95 RON (91 AKI). The insides of my tailpipe are as clean as a whistle, whilst the other one's got hard carbon build up inside the tailpipe. The surrounding of the tailpipe on the other vehicle is also caked in black carbon. There's also soft carbon in there as well - if you take a piece of tissue paper, you can wipe it right off, but the hard carbon remains stuck to the metal.

Sure, I've run CRC Fuel Injector Cleaner and Liqui Moly Fuel Injection Cleaner a few times, but I'm not sure just how much of a difference that would make.

Could the carbon build up be linked into the octane rating, using a higher octane than recommended, or the quality of the gas being used?

Probably a slow short trip driver. I would run 2-3 cans of seafoam through that engine and then do the Italian tune up.

 

[Shannow]

Originally Posted By: Clevy
Originally Posted By: crazyoildude
higher octane usually means more carbon. I have seen it many times

Ditto. More octane equals harder to burn and can lend to incomplete burn. Could be why there is more detergent in premium?


Nope, not even close.

It's resistance to auto-ignition, not difficulty in burning.

 

[GearheadTool]

Originally Posted By: Shannow
Originally Posted By: Clevy
Originally Posted By: crazyoildude
higher octane usually means more carbon. I have seen it many times

Ditto. More octane equals harder to burn and can lend to incomplete burn. Could be why there is more detergent in premium?


Nope, not even close.

It's resistance to auto-ignition, not difficulty in burning.


crazyoildude seems to be flunking out on gas advice?

 

[Clevy]

Originally Posted By: GearheadTool
Originally Posted By: Shannow
Originally Posted By: Clevy
Originally Posted By: crazyoildude
higher octane usually means more carbon. I have seen it many times

Ditto. More octane equals harder to burn and can lend to incomplete burn. Could be why there is more detergent in premium?


Nope, not even close.

It's resistance to auto-ignition, not difficulty in burning.


crazyoildude seems to be flunking out on gas advice?

So am I I guess. I meant to put a question mark at the end of both those sentences because I noticed the same thing but I don't know for sure.
I'm gonna go to gas misers and look into why I've noticed more soot when high octane is used.
My hemi has been leaving black soot in the frost behind the tailpipe on the rear quarter. I assumed it was the premium cleaning something because my mustang Ives on shell v-power and I've not seen any soot at all. And the mustang has no cats if that makes a difference.

 

[crazyoildude]

mech i see it all the time...

 

[crazyoildude]

i guess all the years working in a family owned engine shop and now owning it i learned nothing. but i like the way you think, that kind of thinking keeps us very busy in the shop.. i have to keep as you say "flunking out on gas advice" uh huh.
Its always best to use the octane specified in your owners manual.. if your car requires regular than use it it wont hurt if you put in higher octane once in a while but do it all the time and it will lead to trouble. We see a lot od 4.0 jeeps that have what sounds like a loud knocking noise in the engine and it is almost always caused by high test same with the older northstars that required high test some of them sounded like they were going to blow any minute we would clean the carbon and they sounded like new.

 

[mechtech2]

crazy -
My uncle was a chemist for Standard Oil.
He disagrees with your views on high octane leaving more deposits nowadays.
If any thing, the extra cleaners leave less deposits.
You are attributing what you want to any carbon that you see.
It makes no chemical sense.