An oil flush sounds like a good idea at first. It’s supposed to remove oil sludge, particulate matter, and other deposits to keep the engine running clean. The risk with an oil flush is that those released deposits could end up in places they don’t belong. It can also expose cracks in oil seals and other areas, leading to new, and unnecessary oil leaks.
So, before blindly having an oil flush performed, you need to educate yourself on the possible benefits and potential risks. Especially if you’re thinking about having the flush performed before selling or right after buying a used car!
What is an Engine Oil Flush
An engine oil flush is an advanced maintenance procedure used in some older cars that have a history of poor engine oil maintenance practices. The process starts by introducing a specialized cleaning solution or “Flushing Agent” to the engine oil system.
This dislodges and removes accumulated particulate debris, sludge films, and other contaminants from the engine’s oil system. It’s usually done right before an oil change, to improve the overall health and performance of the engine.
Yet some older engines might benefit from a small amount of oil film from sludge. It’s also possible for an excess amount of oil sludge released in the engine to cause clogs in oil galleries, and other sensitive engine components.
So, there are some oil flush risks to consider, and signs of a problem to look out for.
Benefits of an Engine Oil Flush
An oil flush offers some impressive benefits when it comes to engine oil maintenance and performance. Especially if you have a bad habit of going too long between oil changes.
1. Improves Fuel Efficiency
An oil flush helps the engine to run smoothly by removing contaminants and particulate matter that can cause the oil breakdown while increasing viscosity. It takes less energy to circulate clean oil through a clean engine, which shows up as improved fuel efficiency.
2. Reduces Emissions
Proper engine oil maintenance practices give you the best possible chance of passing an emissions test. An oil flush helps remove deposits on the piston rings that can cause the piston rings to stick slightly. This can prevent them from burning oil.
3. Less Risk of Overheating
An oil flush reduces friction inside the engine’s many moving parts, which helps the engine block maintain a safe operating temperature. This also helps prevent oil oxidation to maintain the oil’s optimal lubricating properties.
4. Prepares the Engine for a Fresh Oil Change
A lot of DIY mechanics will perform an oil flush right before doing an oil change. Removing the sludge and deposits from the engine gives you a clean slate. It can also help maximize the lifespan of the fresh oil going into the system.
Risks of Flushing Engine Oil
Potential problems with an oil flush come when dislodged sludge and particulate matter become trapped in places they should be. They can clog the oil filter, and wreak havoc with a variable valve timing engine. Stripping away oil sludge with an oil flush can also expose the seals leading to oil leaks or affecting the piston compression causing the engine to start burning oil.
1. Clogging the Oil Filter
Dislodged sludge from an oil flush can accumulate and clog the oil filter. Even if the oil filter has recently been changed.
This can have a double-whammy effect on the engine oil system. Depending on how badly clogged the oil filter is the oil pump might struggle to draw sufficient oil up to fully lubricate all the engine’s moving parts. This is especially troublesome at start-up during cold weather.
The longer you go with a badly clogged oil filter, the more strain the oil pump goes through. This can cause the oil pump itself to fail.
Pro Tip
If you recently performed a DIY oil flush and the oil warning light stays on for a few seconds longer than it should have at start-up, the filter might be partially clogged. The wise move is to perform a complete oil change with a detergent-enhanced synthetic oil and a brand-new oil filter.
2. The Car Starts Burning Oil
One of the biggest engine oil flush risks in an older car is that you remove the existing oil film on the cylinder walls and around the piston rings. This can allow oil to remain inside the cylinder during the combustion process causing it to burn oil.
This isn’t as much of an issue with newer cars. However, it could lead to serious complications in an engine that is more than 10 or 12 years old.
3. Clogs in the Oil Galleries
One of the more serious problems with an oil flush is that the dislodged oil sludge and particulate matter can start to clog oil galleries within the engine block and cylinder head. If the clogs are thick enough, they can block the oil flow, which starves critical moving engine components of the lubrication they need to move smoothly.
Since you can’t see what’s going on inside your oil galleries, these clogs can build up unchecked. It can even cause excess wear on the bearings.
Suddenly you notice the engine is running a little too hot. It could overheat when you least expect it, damage a piston, or even throw a rod.
4. Clogs in the Variable Valve Timing Solenoids
If your engine has variable valve timing, you should avoid an engine oil flush in all but the most extreme of cases. The risk is that the oil flush will loosen sludge and oil contaminants which become trapped in the tiny holes of the hydraulic components of the variable valve timing solenoids.
Pro Tip
If you recently had an oil flush and your variable valve timing engine starts idling rough, or shaking while you sit at a stoplight, the sludge deposits are affecting the system. A lot of these VVT engines have tiny screens near the solenoids that can gunk up with dislodged particulate matter.
If you catch it early, and take it to a mechanic, they might be able to clean the VVT solenoids and hydraulics before it causes serious damage to the engine.
5. Older Oil Seals Can Start Leaking
One of the problems with oil flushes that you see in older cars is that oil seals that previously didn’t leak, start leaking afterward. As these seals age, they start to get tiny cracks and degraded sections, that a mild amount of oil sludge will help seal.
When you perform an oil flush, these minor sludge deposits are cleared away, exposing the cracks. The pressurized oil exploits these areas, and the car starts leaking oil.
In just a few weeks, the cracks can worsen to the point that the seal blows out as a massive oil leak.
How to Prevent Needing an Oil Flush
The easiest way to reduce the risks of flushing engine oil is to simply change the oil on schedule. Choose a high-quality synthetic oil enhanced with detergents that are formulated to help control sludge formation.
If you’re making your own oil change, make sure to also change the oil filter. Then use a high-quality replacement filter, which will catch particulate matter before it has a chance to build up sludge.
Frequently Asked Questions
Is it a bad idea to flush the engine oil before selling a car?
If you’re selling a car, it might be a bad idea to perform an oil flush before letting a prospective buyer take a test drive. The concern is that the oil flush releases sludge and particulate matter that then clogs oil galleries or the variable timing system. It could even cause the car to start burning oil by exposing the oil seals or causing oil leaks.
Can flushing engine oil void a vehicle’s warranty?
A professional oil flush shouldn’t void a vehicle’s warranty. Yet there could be an issue in the warranty language if you perform your own oil flush, and the car is still within the extended warranty period from the dealership. If dislodged sludge clogs an oil gallery or the variable timing solenoids, after a DIY flush, the dealership might not honor the repair costs.
How long can synthetic oil hold the particulate matter in suspension?
Some synthetic oils with modern-day detergents claim to be able to prevent oil sludge for up to 20,000 miles. However, these are the claims of chemists and oil company marketing managers. I wouldn’t recommend pushing your luck beyond 10,000 miles before getting another high-quality oil change with filter replacement.
Conclusion
There are some risks of flushing engine oil in an older car that’s been properly maintained. Modern cars that use detergent-enhanced synthetic oils that get routine oil changes shouldn’t need an oil flush. Oil flush problems from dislodged sludge in oil galleries or clogging the solenoids of a variable valve timing engine can do more harm than good.
In some older vehicles, a light patina of oil sludge can help seal the pistons, as well as prevent exposing oil seals. If you perform an oil flush with a properly maintained engine like this, you could start burning oil or leaking oil out of a compromised oil seal.
Sound engine oil maintenance practices are the best way to avoid needing an engine oil flush. For an older car, opting for an oil change with a high-quality synthetic or synthetic blend that has special detergents to prevent sludge buildup is worth the money.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.