Bad carbon on pistons - how to clean?

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19jacobob93

19jacobob93

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Feb 12, 2014
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Gold Coast, QL, Australia
When I replaced my spark plugs 3 days ago I looked through the hole and saw what looked like pretty severe carbon buildup on top of the pistons.
They literally looked like the bottom of a very old baking tray, very black and course looking!

I think this could be a combination of a few things including using the cheapest 91 RON fuel, I've only just changed the original clogged/sludged up fuel filter last week, the spark plugs I took out were gapped 40% too close, oil may be leaking into the chambers through the spark plug housing seals (noticed dark oil on thread of old plugs) and also the car has been doing a lot of highway miles this year sitting at around 1,550rpm most of the time.

Maybe it's from a combination of the above and whatever happened during the 115,000kms before I bought it.

May I add the car still runs great and smooth but I still want it cleaned. I have recently been hearing a sharp metallic sounding rattle on acceleration (not lifters, they are making a different rattle!) which I suspected to be pinging and now I've seen the top of the pistons it's not looking good
frown.gif


I bought a 2 pack of Valvoline injector and valve cleaner because they were only $9 for the pair. It said on the box to put 1 bottle per (up to) 70 litre/quart tank, but I've been tripling that dose, putting a full bottle into about 1/3 of a tank. Is this a bad thing to do?

Does throttle body cleaner remove carbon from the top of the pistons as well? And would I benefit from running a tank of 98 RON (Shell V-Power) through?

Thanks!
 
A lot of folks swear that water mist in the intake of a hot revving engine will steam clean the pistons, exhaust valves and so on. Plenty of clips on YT.

The way I see it unless you hydro lock your engine there is no harm in trying.
 
My two cents, use a cleaner that has PEA (I believe the Valvoline you are using does. My favorite is Techron. Not sure if that is available in Australia though). I don't think using a higher RON (or R+M/2 Octane here in the U.S.) is going to do anything for you unless you are truly knocking. I'm no expert though.
 
Might try the water mist, I noticed that the best way to clean the barbecue after a good use (which looks similar to my pistons!) is to spray water on it when it's fully hot so it makes sense
And I wanted to try a higher octane fuel because reading the fuel descriptions whilst filling up, v-power 98 says it cleans the engine and acts as a UCL, where as the 91 I'm using now only says suitable for most engines. Also if the noise is bad pinging a 98 should help, if not it's something else rattling!
I'll see how the valvoline stuff goes, it doesn't say exactly what it contains apart from being 76% hydrocarbons, where I noticed the cheaper brand ones are 90-100% HCs so it must have some other secret additives!
 
Spraying clubsoda in the intake at about 1200-1500 rpm works great. The carbon dioxide works really effective.
 
Originally Posted By: shDK
Spraying clubsoda in the intake at about 1200-1500 rpm works great. The carbon dioxide works really effective.


Not trying to criticize, but since I've never heard of this, can you provide some sort of evidence to back this up?
 
Go to repco or cheapa auto spares in oxen ford and buy a bottle of three bond engine cleaner and spray some in the throttle body and down the spark plug tube expect lots of smoke and clean pistons
 
Originally Posted By: tony1679
Originally Posted By: shDK
Spraying clubsoda in the intake at about 1200-1500 rpm works great. The carbon dioxide works really effective.


Not trying to criticize, but since I've never heard of this, can you provide some sort of evidence to back this up?


Club soda is carbonated water.
 
I would do an overnight piston soak through the spark plug holes with either GM top engine cleaner or Chrysler stuff.
I believe Subaru has one also but have no info on it.

Put about 2 ounces down each plug hole on a warm engine and screw the plugs back in loose just to keep junk from falling in, let it sit overnight.
Before starting the car remove the plugs, disable the fuel injection and ignition then crank the engine a few revolutions.
Reinstall the plugs and fire it up.

You can then use a PEA based cleaner to either maintain or finish the job.

Edit: just because its black doesn't necessarily mean it need cleaning, a carbon layer on the pistons protects the piston heads. It only becomes an real issue when its excessive and you get carbon knock or other symptoms of excessive carbon.
 
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Maybe you're getting oil carryover into the intake from the PCV system. If you're getting spark knock under hard acceleration, that's probably the oil being inducted to the cylinders from the intake.
 
Fill the WW reservoir with 6% USP H2O2 shove one of the hoses into the intake log using a needle valve (as use to inflate a futbol). Confirm a good but not excessive mist before connecting. Hit the spray when you are running WOT IN 3RD gear on the motorway revving up and down 3K-5K rpm WOT. Only inject at WOT. You will like ly need fresh plugs and an OC after this exercise.
 
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If it is working and then pls leave it alone :)
if you dislodge the carbon, you egr valve will get clogged and you will be replacing it or cleaning it.

you could dump couple of bottles of valvoline cleaner and drive at a higher rpm by downshifiting.
 
Originally Posted By: Testoprop
Go to repco or cheapa auto spares in oxen ford and buy a bottle of three bond engine cleaner and spray some in the throttle body and down the spark plug tube expect lots of smoke and clean pistons


I've heard a few people recommend 3 bond including mechanics and people who've used it and had good results.
I believe 3 bond is the Subaru stuff from what I've heard
 
I've tackled this two ways in the past;

If the head is off then brake cleaner, enough time for some coffee and a cigarette, and a quick wipe with shop towel has always worked for me I the past ( different petrol over here
wink.gif
)

If the engine is staying in one piece then a full bottle of redline si1 goes into approx. Half a tank of fuel, a good drive to get Upto temperature followed by a water mist down the intake, another drive to get rid of any remaining water, and then an overnight piston soak through the plug holes as Travel said.

To stop future recurrences use high quality fuel and a maintenance dose of Si1, occasional hard driving/WOT, and if you want to feel like you've done everything in your power to stop it vent the pcv to atmosphere and blank off your egr valve.
 
I think this might be a case of "if it ain't broke, don't fix it". Unless you can prove that the carbon is causing problems, you might make things much worse or cause other issues trying to clean it out.

The only thing I would do here is probably use one of the PEA-rich cleaners in your tank of gas:

Amsoil Performance Improver
Chevron Techron Concentrate
Red Line SI-1
Gumout Regane
 
Originally Posted By: Trav


Edit: just because its black doesn't necessarily mean it need cleaning, a carbon layer on the pistons protects the piston heads. It only becomes an real issue when its excessive and you get carbon knock or other symptoms of excessive carbon.



So glad to see this posted... its absolutely true. Its perfectly normal for piston crowns to look dark, even pitch black, and slightly rough. Ideally there should not be any carbon built up thickly, but a thin film almost always happens. Its when you start getting globs of carbon as thick as a fingernail or more that you need to worry. Until that point, any "cleaning" you do is potentially more harmful than good (washing oil off cylinder walls, washing dislodged grit down into the ring spaces, etc.).
 
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