A piston soak is one of the most effective DIY ways to clean the top of an engine.
Before & After — What a Soak Can Do
Carbon builds up on piston crowns and in ring grooves over thousands of miles.
Before — carbon buildup
After — clean piston crown
Illustrative results from the piston soak procedure.
What is a piston soak?
Over time, combustion leaves hard carbon deposits on top of the pistons.
💡 When it helps most.
What you'll need
- Berryman B-12 Chemtool
- Spark plug socket, ratchet and extension
- Gloves, eye protection and good ventilation
- A few clean rags
- Fresh engine oil and an oil filter for afterwards
How much B-12 per cylinder?
| Situation | Amount per cylinder | Soak time |
|---|---|---|
| Light maintenance | ~30 ml | 12 hours |
| Oil burning | ~45 ml | 12–24 hours |
| Stuck rings | ~60 ml | 24 hours+ |
Don't overfill.
Step-by-step piston soak
Remove the spark plugsLet the engine cool.
Position the pistonsIdeally rotate the engine by hand.
Pour in the B-12Add the amount from the table.
Let it soakLeave it for 12–24 hours.
Expel the fluidCrank the engine briefly.
Reinstall and startRefit the spark plugs.
Change the oilChange the oil and filter promptly.
⚠️ Safety first.
What results to expect
On a carboned-up engine, people commonly report smoother idle.
Frequently asked questions
How long should I let it soak?
12 hours for general cleaning.
Do I really need to change the oil afterwards?
Yes.
Can I do this on a motorcycle, mower or marine engine?
Yes — the same principle applies.
Will it damage my catalytic converter?
Burn-off is brief.