Removing carbon from piston tops

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wavinwayne

wavinwayne

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This morning, I did my yearly change of the spark plugs in my '00 VW GTI 1.8T. In previous years, I've never paid much attention to what the pistons looked like. Today, however, I took a good look down through the spark plug holes. Two of the four pistons were approx 1/2 covered in a layer of black carbon.

Before I put the new plugs in, I sprayed a copious amount of Seafoam into each spark plug hole, wetting down the entire top of all the pistons. Interestingly, when I cranked her up, there was no smoking at all. That was strange. I have no clue if the Seafoam spray removed any of the carbon. After I had installed the new plugs, I took the car for a test drive. After letting it get up to normal operating temp, I did a few WOT runs, which I've heard can remove carbon from the pistons. Not sure if there's any truth to that, but a WOT run in the VW is fun anyway.

Upon my return home, I decided to attempt a distilled water de-carb procedure. I detached a vaccum line from a non-return valve on top of the throttle body. The VW DID NOT LIKE HAVING THE VACUUM LINE REMOVED. It let out a horrible sounding hiss, sputtered horribly & would barely idle, so I decided to nix the water de-carb idea; it just seemed too risky. Instead, I sprayed approx. 1/4 of the spray can of Seafoam into the vacuum hose at the throttle body, with the warmed up engine running. This was working well for a few minutes, then it started smoking a little from the exhaust, so I decided that was enough tinkering for today. I didn't want to P-off my neighbors (I live in a condo with mostly old folks as my neighbors), plus I didn't want white Seafoam smoke filling up my garage.

With all that stated, is there anything really detrimental to having a little carbon build-up on the top of the pistons? Gas mileage & performance don't seem to be suffering. If the carbon needs to be removed, what is the preferred method of doing so? Maybe FP, or Lucas UCL, or some other type of fuel system cleaner in the gas tank? Any suggestions and/or comments?
 
But do consider why its on those two cylinders. For me it was the clogged PCV and line. What did those two plugs look like compared to the others? injectors , bad spark or wires to those plugs?
 
Not sure why the two cylinders were that way. No DTC codes to speak of. The car runs fine. Here's a pic. of the plugs, not necessarily in the order they were removed from the engine:
Plugsat87kmiles.jpg
 
FWIW, the plugs shown above were run for approx. 25k miles, a little over one year in the GTI. They were $2 each. Replacements are the same as the ones pictured.
 
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Doesn't your 1.8T spec. multi ground plugs. The 1.8T's I've seen have plugs with three grounds.

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No. My VW 1.8T spec's NGK platinum plugs, as pictured here when I replaced the OEM plugs back in '05.

OEM-NGK-3.jpg
 
In my experience, cheap plugs (no special metal electrodes) perform okay for 5k-10k miles in a stock 1.8T. Denso Iridium did well for 30k-35k miles and NGK Double Platinum for 35k to 40k miles. It doesn't pay to go cheap on plugs for this engine that eats plugs.
 
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In my experience, cheap plugs (no special metal electrodes) perform okay for 5k-10k miles in a stock 1.8T.....It doesn't pay to go cheap on plugs for this engine that eats plugs.

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The plugs I removed today did just fine for 25k miles in my stock 1.8T. It didn't "eat" the plugs.
 
Aren't the "correct" plugs of the double platinum variety, and available from Autolite for $4/plug? Can't spare the extra $8 every few years? I bet you spend more on bicycle chain lube.

Anyway, the carbon is fine and just leave it alone unless its causing problems. You'll probably do more harm by sending a cloud of junk through your catalytic converter each time you try to clean it out unsuccessfully. Besides, I would've done all of your "cleaning" PRIOR to the install of new plugs, not after.
 
It could be due to engine design but I add 6 - 10oz of Marvel's Mystery Oil to 90% of every fill up and the piston tops of the 2.2L I4 in my Honda stays pretty clean. When I first purchased the car (used) the piston tops were black but now they're a dull metallic grey when I changed out the plugs 11k later.

This car tends to run rich (factory settings) using premium fuel and copper NGKs.
 
Hmmm, that carbon on the piston tops is pretty normal.
I would not try loosen it up like you have been doing since you run the risk of doing some damage or getting a piece of that hard carbo stuck above the rings or worse...
If you have ever taken a motor apart you will know just how hard that stuff is...it requires an acid bath or scraping to remove it.
I would just leave it, a little bit does no harm.

Do you use premium unleaded or Lead replacement gas?
 
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Aren't the "correct" plugs of the double platinum variety, and available from Autolite for $4/plug? Can't spare the extra $8 every few years? I bet you spend more on bicycle chain lube.

Anyway, the carbon is fine and just leave it alone unless its causing problems. You'll probably do more harm by sending a cloud of junk through your catalytic converter each time you try to clean it out unsuccessfully. Besides, I would've done all of your "cleaning" PRIOR to the install of new plugs, not after.

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Mike,
When I purchased these $2 Autolite copper plugs, I saw Autolite Platinums, don't think they were double platinum, though. $4 each. Really, I just wanted to see how well a cheap copper plug would perform in my 1.8T. I was well pleased, so I decided to use them again.

When I removed the old ones on Monday, had I not liked the looks of them, the car would have stayed parked until I could get the OEM NGK's. Since the plugs were just barely over the spec'd gap after 25k miles, & I was pleased with their overall appearance, I used the same ones again.

Yes, I could spare the extra $8 a year for "better" Autolites, but at this point, I don't see the need. Also, you're right; I do spend more on bicycle chain lube every year than I do on spark plugs.
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Out of curiosity, why do you say that the carbon on the pistons is ok? As far as doing the cleaning before removing the plugs, it was not feasible since Monday was really the only day I had scheduled to work on the car, and the engine had to be cold to do the spark plugs.

I dumped all sorts of cleaning stuff into the Expedition, via the brake booster vacuum line a couple years ago. Shortly thereafter, I changed the plugs. I could find no signs of fouling or anything else out of the ordinary, so it didn't concern me to do the cleaning on the VW with new plugs. FWIW, I think I'm done with trying to clean the VW via a vacuum line; it just scares me too much.
 
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It could be due to engine design but I add 6 - 10oz of Marvel's Mystery Oil to 90% of every fill up....

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In your opinion, what effect does the MMO in your fuel have on the fuel's octane rating?
 
You should try the NGK Iridiums...I use them in my OPEL and they last and perform very well.

A little bit of carbon on top of the pistons isn't going to hurt.
Just remember that car is a turbo car with a catalyst, so all the muck you throw into the pots ends up having to go through the turbo and the catalyst and could cause damage...
Its only a problem when its very thick deposits, but then you would be better off taking the head off and scraping it off...but we are talking super high mileage here...unlikley scenerio.
 
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Hmmm, that carbon on the piston tops is pretty normal.
I would not try loosen it up like you have been doing since you run the risk of doing some damage or getting a piece of that hard carbo stuck above the rings or worse...
If you have ever taken a motor apart you will know just how hard that stuff is...it requires an acid bath or scraping to remove it.
I would just leave it, a little bit does no harm.

Do you use premium unleaded or Lead replacement gas?

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I guess I'll take you guys' word for it, and not try cleaning the carbon again. I didn't realize I was doing anything that dangerous for the engine. Now I know better.

FWIW, I've never taken an engine apart, but I did have to manually remove the throttle body elbow, to de-carb the EGR passages on my wife's Expedition 4.6L last year. You're right, the carbon deposits are very hard. I had to use a .223 caliber bore cleaning brush to scrape it off. Solvents didn't even touch that stuff.

To answer your last question, I use only unleaded gas, no particular brand loyalty, mostly 93 octane, sometimes 89 octane. Depends on how much of a penny-wise, pound-foolish cheapo I am being on any given day.
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