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Discussion Starter #1 (Edited)
Based on the results of a recent dry and wet compression test, I believe the 4.7L V8 SOHC engine in my '02 Dodge Dakota Club Cab 4x4 may have some piston rings that are somewhat stuck in the piston ring lands and are failing to properly seal against the cylinder walls. While it's certainly possible the rings are worn rather than simply sticking, the truck has only 104,000 miles and the cross-hatching is still visible on the cylinder walls.

In addition, I believe the truck may not have been maintained by the book by its previous owner(s), and think it quite possible that carbon and/or sludge build-up may be a factor in preventing the rings from moving freely in the lands. Other than the drive home, I have not put the truck on the road as of yet due to other repairs that I am currently tackling, so I can't say whether the truck burns any oil. However, I can say that there is no noticeable discolored smoke from the exhaust.

I've read that others in similar situations have had success performing a 24-48 hour "piston soak" by introducing some form of solvent into the combustion chamber and allowing it to soak the piston head and drain past the rings. While I have the spark plugs out and a compression gauge test kit handy, I figure such a test would be well worth my time.

Based on what I've read elsewhere, the solvent of choice for such an application often appears to be Marvel Mystery Oil. I've researched MMO extensively and am more comfortable with its use for this application than more aggressive solvents like diesel or kerosene, although I am open to suggestions.

My questions for others who have performed a "piston soak" are as follows:
  1. How much solvent should you add per cylinder? I would think you would want to add enough to cover the top of each piston so the full circumference of the ring can soak properly. Anyone have a read on how many ounces this is? I've read anywhere from 2-4 oz. per cylinder online.

  2. At what position of the crank in relation to TDC will all of the pistons be positioned mid-way in their bores? This will make it much easier to add the proper amount of solvent to each cylinder.

  3. How long of a soak is required for it to be effective?

  4. Rotating the engine slowly by hand at various intervals is often recommended. How far should it be rotated and how often?
Would love to hear any and all tips or ideas from other 4.7L V8 SOHC owners who have performed piston soaks in the past. Thanks in advance!
 

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I would just remove the plugs and throw a shot of PB Blaster or seafoam in the cylinders, let soak overnight and go for a high-revving carbon run/Italian tune


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