Using ATF to clean valves?

[dieseltrooper]

Has anyone heard of this? Sounds very shade-tree to me....
Drizzling ATF into the carb bores while revving the motor. supposedly cleans carbon off the valves/pistons.....

 

[Opus Dei]

I've heard it, too. The people that tout it point to the smoke billowing, and say "look, there goes all that carbon".

I can't see how introducing an oil into the combustion chamber would remove almost ceramic-like depositions. And I don't know how it would have time to scour the bore, nor anything caustic to it. Think about transmission fluid that's overheated, or never changed. It makes a nasty sludge and varnish.

 

[clem]

"look, there goes all that carbon"


But a certain amount of carbon build up is important to help seal the engine.

 

[Hamilton Felix]

Pouring WATER through a running engine will remove carbon. Just don't kill the engine.

 

[OddOne]

A well-known trick is to replace one quart of the engine's oil with ATF and drive it for a few hundred miles before changing for fresh oil. The added detergents and seal conditioners in the ATF can clean out varnishing gas and give some dryrotting seals a little more life.

Of course, you don't want to do this all the time, just when needed and only for a few hundred miles.

"look, there goes all that carbon"

But a certain amount of carbon build up is important to help seal the engine.

Not for engines designed for unleaded gasoline. The idea that engines need some carbon for the engine to seal properly hasn't been correct for a couple decades now - increased seal precision thanks to CNC manufacturing has eliminated all benefits from carbon as a seal enhancer.

Carbon could be helpful in one specific instance: Carbon buildup on the piston tops can raise the engine's compression ratio, actually increasing horsepower but also increasing fuel consumption (fuel economy drops as compression ratio increases).

For most modern vehicles the problems from carbon deposit buildup comes from decreased airflow into the induction end of the engine (throttle body to intake valves). Buildup can cake the throttle plate, causing a sticking accelerator pedal and sluggish throttle response. It can also clog idle air control valves, causing stalling and rough-idle problems and at worst kill the IAC valve, which could cost a few hundred bucks to replace.

Modern engines are designed to work best without carbon deposits.

Pouring WATER through a running engine will remove carbon. Just don't kill the engine.

That draws a "yes, but" from me. Yes it'll remove deposits, but it won't free them up from anywhere but the combustion area and that's not the only place you'll get a buildup. Everywhere else requires specialized chemicals to break the carbon up enough to blow out the exhaust.

oO, who helps run an auto repair shop when he's not slinging code...

 

[clem]

I still have a 1966 Dodge Charger. It needs the carbon. Ha!

 

[OddOne]

I still have a 1966 Dodge Charger. It needs the carbon. Ha!

Thbbt.



oO

 

[intothatgoodnight]

OddOne comments:

"Carbon buildup on the piston tops can raise the engine's compression ratio, actually increasing horsepower but also increasing fuel consumption (fuel economy drops as compression ratio increases)."

Thread drift here -- one more time, with feeling -- what are the hard core mechanics behind your above statement that by raising the compression, one also increases fuel usage? I have always believed that a higher compression ratio increased the amount of work that was able to be produced by the combustion process.

Although a higher compression ratio can impact the velocity of air/fuel moving throught the induction system, it is not the primary determinant in how much fuel is expended per power stroke -- cam design and fuel/air delivery system (carb, mass airflow device, fuel injector spray patterns) are the main determinants/regulators regarding fuel usage (with everything else adjusted to the same baseline).

Can you clarify?


intothegoodnight

 

[CTCStrela]

It's not really the rise in compression, it's the fact that the carbon on top of the pistons is not uniform in cross section, nor smooth, like a new piston. It has to do with the swirl and mix of gas/air in the combustion chamber.

 

[intothatgoodnight]

CTCStrela notes:

"It's not really the rise in compression, it's the fact that the carbon on top of the pistons is not uniform in cross section, nor smooth, like a new piston. It has to do with the swirl and mix of gas/air in the combustion chamber."

How does this non-uniform carbon buildup on a piston top INCREASE the amount of fuel used during a combustion cycle? Piston dome shaping, either intentional or not, generally has little direct effect on the amount of fuel moving through the induction system, per se. Intentional piston dome shaping is usually intended to raise the compression and/or assist in the actual combustion burn process.


intothegoodnight

 

[CTCStrela]

It doesn't increase the amount of fuel brought into the cyl per revolution, it decreases the combustion efficiency..ie less fuel burned, less power per throttle setting...less mpg.

 

[intothatgoodnight]

CTCStrela continues:

"It doesn't increase the amount of fuel brought into the cyl per revolution, it decreases the combustion efficiency..ie less fuel burned, less power per throttle setting...less mpg."

Never heard of such a thing -- assuming all things elsewise being equal, a bit of bumpy carbon on a piston top cannot contribute any noticeable amount to a gas mileage DROP.

In my query, I am not considering a piston top covered in a deep layer of (perhaps wet) carbon, perhaps caused by a leaking valve seal/guide or piston rings that are unable to maintain their intended soundness -- rather the light carbon layer that occurs over many, many miles in a cylinder that has not lost its oil control integrity.


intothegoodnight

 

[CTCStrela]

Well, add on to that the fact that carbon on pistons creates combustion hot spots, that can cause pre-detonation, which makes you turn the advance back on the distributor, which makes you less mpg...

 

[CTCStrela]

Into, if you have a bad swirl in combustion chambers, you are getting less uniform combustion. IE less boom for the amount of gas going into cylinders. That means to go say 50 mph, you need to put more fuel into the engine to produce the power nessicary to push the car at that speed. IE worse mileage..

 

[intothatgoodnight]

CTCStrela replies:

"Well, add on to that the fact that carbon on pistons creates combustion hot spots, that can cause pre-detonation, which makes you turn the advance back on the distributor, which makes you less mpg..."

Good point -- assuming that the carbon buildup is "normal" and not caused by excessive oil bypass egressing into the combustion chamber.

One might simply try running higher octane gas to reduce pinging, or perform the above mentioned "water trick" of carefully pouring small amounts of water down the intake while the engine is running at a steady 2500 RPM, in an attempt to break up normal carbon deposits layered in and around the combustion chamber.

Other causes of pinging in higher mileage/older engine can be attributed to:

• mixture problems caused by malfunctioning carburetor or fuel injection unit/injector

• vacuum leaks from dry-rotted rubber vacuum connection hoses or leaking induction system gasketing.

• worn distributor shaft bushings, allowing the distributor timing to wander,

• frozen or sticky distributor mechanical advance mechanisms,

• stretched/worn cam timing chain/gears, which are allowing negative cam timing changes, and associated disruptions to induction system airflows and cylinder pressures, and/or

• worn cam lobes,

"Into, if you have a bad swirl in combustion chambers, you are getting less uniform combustion. IE less boom for the amount of gas going into cylinders. That means to go say 50 mph, you need to put more fuel into the engine to produce the power nessicary to push the car at that speed. IE worse mileage.."

Bad swirl from what? Normal carbon build-up? It would be unusual for normal carbon build-up to cause a swirl disruption that resulted in a measurable impact to power and gas mileage -- possible, but unlikely. Remember, carbon build-up ALSO raises the static compression ratio, thereby increasing the amount of work accomplished per given combustion cycle.


intothegoodnight

 

[CTCStrela]

PCV can make a mess of it all, also, lol.

 

[OddOne]

Thread drift here -- one more time, with feeling -- what are the hard core mechanics behind your above statement that by raising the compression, one also increases fuel usage? I have always believed that a higher compression ratio increased the amount of work that was able to be produced by the combustion process.

Although a higher compression ratio can impact the velocity of air/fuel moving throught the induction system, it is not the primary determinant in how much fuel is expended per power stroke -- cam design and fuel/air delivery system (carb, mass airflow device, fuel injector spray patterns) are the main determinants/regulators regarding fuel usage (with everything else adjusted to the same baseline).

Can you clarify?

An increase in compression ratio -always- requires more fuel, requires fuel with a lower burn time, and reelases more energy in a DISproportional amount. A 350 smallblock, for example, might make ~225HP at 2400 RPM with 9.5:1 compression and get 22 MPG off 87 octane gas. Replace the pistons (ONLY) and bump the ratio to 10.5:1 and you'll drop to like 14 MPG but the horsepower at the same rotation speed will go up to around 350, and as a result you'd need to run 92 octane or it'd ping as the 87 won't burn slowly/long enough to drive the pistons through the now longer (in terms of ratio) power stroke.

Now, how this applies to modern engines and carbon buildup on piston tops:

As the compression ratio increases, the "sweet spot" for efficient combustion in terms of fuel vs. air changes. The oxygen sensors detect the change and report it to the ECM (Engine Control Module, the engine computer) as a lean condition. As the compression increases over time from the carbon buildup, the ECM will detect the engine leaning out, and will compensate by raising the long fuel trim, which in turn will use more fuel.

I've seen this in the real world hundreds of times, and have literally WATCHED the long fuel trim on carboned-up engines come back to within 3% of baseline from as much as 15-18% positive (trying to enrich the engine) while being decarboned. OBD-II graphing scanners are handy devices.

The ECM is constantly looking for optimum efficiency by checking every aspect of the engine that you mentioned. Changing ANY ONE ITEM changes fuel consumption in some way, although which way and by how much depends on what's changed and how/how much.

It's not really the rise in compression, it's the fact that the carbon on top of the pistons is not uniform in cross section, nor smooth, like a new piston. It has to do with the swirl and mix of gas/air in the combustion chamber.

While that explanation is plausible, the engines I've seen all had uniform enough coatings to negate this being a likely cause. I'd say this is a factor but only a minor one. Generally it's the aforementioned computer compensating for the lean caused by the compression ratio change that causes the increase in fuel consumption.

That said, however, carbon deposits -do- absorb fuel spray. So, if an injector is hitting a carbon deposit directly (think direct- or port-inject systems, as compared to throttle-body injection), the fuel will soak in and vapors be released until the carbon's heated to the fuel's vapor point, and that can cause secondary ignition ("dieseling") until the engine reaches its normal operating temp.

oO

 

[intothatgoodnight]

OddOne replies:

"An increase in compression ratio -always- requires more fuel, requires fuel with a lower burn time, and reelases more energy in a DISproportional amount. A 350 smallblock, for example, might make ~225HP at 2400 RPM with 9.5:1 compression and get 22 MPG off 87 octane gas. Replace the pistons (ONLY) and bump the ratio to 10.5:1 and you'll drop to like 14 MPG but the horsepower at the same rotation speed will go up to around 350, and as a result you'd need to run 92 octane or it'd ping as the 87 won't burn slowly/long enough to drive the pistons through the now longer (in terms of ratio) power stroke."

I understand the issue of needing a higher octane fuel to properly power a high-compression engine -- removing this from the discussion, lets just say that the low compression and high compression versions of your hypothetical engines were both running high octane gas.

You state that "an increase in compression ratio -always- requires more fuel". What is the SCIENCE behind this statement? A higher compression engine will perform more work in a given combustion cycle than a lower compression engine -- assuming, in your example, that the only change made was to replace low compression with high compression (however it may be done -- head milled, thinner gasket, domed pistons, or a combo of the three), and assuming that the change was not significant enough to alter the fuel-to-air ratio (I know -- hang with me here) -- then what is the SCIENCE driver behind a raised compression requiring MORE fuel, by virtue of simply raising the compression? Are you suggesting that raising the compression ALWAYS leans out the mixture, requiring an additional fuel amount to be added? Why, if so? What if I change the cam to increase the amount of overlap and decrease the cam centerline, thereby lowering cylinder pressures in the high compression engine, and also lowering the propensity of the high compression engine to ping?

Interesting thoughts you have provoked -- I currently own a high-compression muscle car, and have owned several different makes/models musclecars over the past 30 years -- all were at least 10.5:1 or higher compression -- all were/are carbureted, and all have/do get abysmal gas mileage, by the simple virtue that none were designed for gas mileage -- strictly point and shoot, straightline performance. And, I am VERY familiar with the need to run racing gas (even though the car is not raced, per se) since 92 octane pump gas is wholly incapable of preventing pre-ignition in older high compression engine/cam/induction system designs.

Your argument brought to mind a story -- my teenage friend's father's owned two similar Oldmobile 98s -- one was a 1970 with a hi-comp 455, and the other was a 1971 with a low-comp 455 -- essentially the same car, weight was similar -- hi-comp 1970 Olds car was able to get 15 MPG on the road, if you kept your foot out of it -- low-comp 1971 Olds car, driven on same trip and in similar fashion, could only manage a paltry 11.5 MPG, and was noticeably less powerfull -- carb and plugs showed proper mixture -- tried changing metering rods and hangers -- not much improvement. Decided to change cam in low-comp 1971 Olds car and replace with a specialty grind -- power jumped noticeably, making it nearly as fast as the hi-comp 1970 Olds car, once carb was tweaked out -- but gas mileage only climed to 13.5 MPG.

Above rebuttal is admittedly unscientific, with too many other variables unidentified -- but, as a general rule -- most of my friends and I noticed that once the compression ratios were dropped in all new cars in the 1971-72 timeframe, the gas mileage tended to drop also -- as did the horsepower (obviously).

Or had our foots simply become heavier?

Hit me with the hard science -- comments?


intothegoodnight