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How to Do a Piston Soak to Reduce Oil-Burning Problems


Top view of the pistons with the head removed in a four cylinder engine.

If your gasoline-powered car is burning more oil than you'd like, and you've already tried the simpler approach on this page, then you may want to try doing a piston soak.

A piston soak is a relatively simple procedure on most cars. It works best on engines that have vertical cylinders. The basic idea is that you soak the pistons with a solvent that you pour in through the spark plug holes to dissolve the carbon around the rings.

I used to do piston soaks on Saturn S-Series engines because the oil ring design caused buildup of carbon around the rings that would cause oil burning and reduce performance. Saturn even had a special solvent for this purpose that they used and sold at their dealerships.

The most important thing to remember when doing a piston soak is to make sure that all the solvent is removed from the cylinders before starting the engine. Too much liquid in the cylinders (and it takes very little for this to happen) can cause hydrolock, which can literally cause the cylinders to explode. Have a vacuum pump or a hand brake bleeder at the ready to remove all the solvent when the soak time is finished.

Typical Piston Soak Procedure

These steps assume that you've already disassembled whatever you have to in order to reach the spark plugs. On some cars this will be easy, involving little more than removing the engine cover. On other cars... not so much.

You should use a solvent that has a high percentage of PEA. Redline SI1 (60103) Complete Fuel System Cleaner, Techron Complete Fuel System Cleaner, Gumout 510013 High Mileage Fuel Injector Cleaner, or LiquiMoly DIJectron would all be good candidates.

Step 1: Prepare the Spark Plugs

With the engine cold, remove the spark plugs; then apply an anti-seize compound to the threads, replace the plugs, and torque them to the low end of the specified torque range using a torque wrench. This is to make sure that any corrosion is broken up and to make the plugs easier to remove when you do the actual piston-flush procedure.

Step 2: Get the Engine to Operating Temperature

PEA-based solvents work best at high temperatures, so you need to start with the engine hot.

Step 3: Remove the Plugs and Introduce the Solvent

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Let the engine cool for no more than a few minutes before removing the plugs and introducing the solvent. Using a chemical-resistant funnel, pour the solvent into each cylinder until the piston is fully covered with solvent. Be careful not to burn yourself.

You can stuff the corners of clean shop rags into the holes to prevent foreign objects from getting into the cylinders. You can also use the spark plugs and stoppers; but if you do this, make sure that the starter is disabled by removing the starter fuse or relay, or by disconnecting the negative battery terminal. If someone tries to turn over the engine while the solvent is in the cylinders, it will destroy the engine.

Step 4: Wait

Give the solvent no less than eight hours (but preferably 24 hours) to do its job. This is the actual piston soak.

Step 5: Remove the Solvent and Replace the Plugs

Using a vacuum pump or a manual brake bleeder, remove the solvent from the cylinders. Then use compressed air to evaporate any remnants left behind. There's a chance that most or all of the solvent may have drained into the crankcase, so don't be surprised if that happens.

Once all of the solvent has been removed from the cylinders, turn the engine over for a second or two with the plug holes empty, and then replace and torque down the plugs.

Step 6: Warm the Engine Up and Drive a Few Miles

Start the engine and allow it to warm up to operating temperature, then drive normally for a few miles.

Step 7: Change the Oil and Filter

I suggest that for this particular oil change you use a diesel engine lubricant like Rotella or Delvac that also has an API S-rating meeting your vehicle's requirements, and is also of the proper viscosity for your vehicle. Diesel lubricants have much more powerful detergent packages and will help continue the cleaning process. This oil change will be for an interval of no more than 1,000 miles (about 1,609 kilometers).

Step 8: Add a Bottle of Techron to the Gas

A bottle of Techron or another fuel treatment containing PEA in the gas tank will also help continue the cleaning process.

Step 9: Drive Normally for Up to a Thousand Miles

Check the oil frequently during this time and make a note of any losses. Add oil if the dipstick indicates that it's needed, and make a note of all additions.

Step 10: Evaluate

If your car's oil consumption has been eliminated or reduced to an acceptable level, change the oil and filter again, this time using your usual preferred oil.

If the oil consumption has been reduced considerably, but not as much as you would have liked, you may want to try the piston soak again.

If there has been little or no meaningful reduction in oil consumption, then your vehicle's engine probably needs mechanical repairs. There's no point in trying the piston soak again if there was no improvement at all the first time.

Motor oil being poured from a jug. Laboratory flasks representing synthetic motor oil. A drain pan being used to catch used oil being drained from a car engine. The open top of an engine coolant reservoir. Mechanic using a rooling creeper to work under a car. A hydraulic floor jack being used to raise a car. Three automobile engine oil filters. A mechanic using a wrench to work on a car engine.

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