I've used STP carb cleaner through the brake booster line. I've also done decarbonisation with water (5 quarts at a time), and decarbonisation with a 50/50 mix of water and methanol....these were through a long clear plastic tube (the kind used in fish tanks) inserted into a jerry can of the stuff, at 1500rpm. [ 2 small holes were cut at different points of the long plastic tube to ensure that plenty of air gets mixed with the water being sucked in - this way there's no need to fast dip and remove the tube from the water which is very bothersome.] I've also done direct carb cleaning of the intake valves using a carb cleaner when my intake manifold was removed.
2 weeks ago, I did a piston soak using marvel mystery oil over 24 hours. Last year, i did a piston soak with carb cleaner and ethanol over 3 hours.
1. The first time you do this intensively, it helps, especially the carb cleaner/water decarb through the brake booster fitting. Engine feels more responsive. After that there's no real improvement.
2. Any water that gets into the engine through blowback gases while doing water decarb will be naturally vapourised and expelled through the EGR system over the course of 1 hour's total driving. This can be at one instance or over a few days. Yellow emulsion-like oil will turn back to black/brown. There's no risk to the system. While the water is in the system, the engine will feel artificially smoother, this is a false positive.
3. From what I've read and pondered over, I don't think these methods are practical to remove thick layers of piston-top carbon, at least with the chemicals mentioned above. ANd, i don't think water decarb results in steam cleaning of the combustion chamber as there's probably too litle sustained steam at high pressure. HOWEVER, following a top overhaul, these methods are EXCELLENT ways to keep the piston tops clean (especially the overnight piston soak) if done regularly i.e. once every 6 months. This removes carbon when its thin enough to be dislodged easily by these on-engine methods.
4. The next thing to try would be to use high pressure compressed air or a water jet injected through the spark plug holes after piston soaking has been done. This would dislodge alot more of the loosened carbon. Merely restarting the engine may cause some loose specks to bake onto the piston top yet again due to the high heat. Unfortunately i neither have shop air or a water jet to try this with at the present time.
Let me know what you'd like to do. Its certainly worth a try.
Last edited by robertobaggio20; 09-26-2010 at 12:47 AM.