How to Clean Engine Sludge? Symptoms and Causes

If your engine longevity is a concern to you and you want to keep your engine running nice and smooth, you must do regular check-ups and maintenance. The most important thing for engine longevity is having an appropriate circulation of quality engine oil. Engine oil is the lifeblood of every engine; it cleans and lubricates the internal engine parts and makes its movement friction-free, but that’s not all.  This is just a tip of what it does. Motor oil helps to maintain an engine’s optimum operating temperature, preventing the engine from overheating.

If you don’t want to encounter engine oil clumpy issues, you need to carry out a regular oil change. Failure to do this, your engine oil might clump and stick together and clog your engine in the process. This is known as engine sludge. Those who don’t learn the symptoms and how to clean engine sludge are putting their cars at risk, which could cause severe engine damage resulting in costly repair bills.

What causes oil sludge?

Engine sludge is usually caused by low operating temperature, lousy or poorly designed crankcase ventilation system, crankshaft-induced cavitation, or internal water leaks, and can accumulate over time. Engine sludge can cause poor engine performance or seizure – this typically happens on rare occasions when you neglect to change your engine oil regularly or drive the vehicle with extensively low motor oil. You should periodically change your engine oil to be on the safe side.

engine oil sludge symptoms

Engine Oil sludge symptoms

The only way to see if you have sludge in your engine is by looking at it, and you would have to remove the valve cover. Unfortunately, this is not what a regular car owner can do. But the good news is, that there are engine oil sludge symptoms you should watch out for that shows whether or not you have sludge in your engine. If you encounter any of these signs, it could mean you have sludge in your engine, and it’s time to flush the engine using one of the best engine flush cleaners.

1. Ticking or clicking Noise from the tappet.

When an engine develops sludge, the sludge is usually seen near the tappet areas below the head. The sludge will not allow the tappet and the hydraulic jacks to operate freely, thereby causing a ticking or clicking sound. The reason is that the sludge is blocking oil galleries resulting in not enough oil to lubricate the rams and the springs.

The tappet controls the movement of exhaust valves and air intakes, and they move several times per second, which is why engine sludge is mostly found in these areas. The engine oil breaks down quickly because it starts lubricating many engine components once you turn on the engine. The ticking or clicking continues until you flush the engine. Then, the tappets and springs will start working nicely and smoothly.

2. Low oil pressure and warning light

Since the engine oil sludge can block oil galleries, it will reduce the speed at which the motor oil circulates, and when the engine sludge reduces the oil circulating pressure, it will trigger the check engine light. This can cause catastrophic problems to engine-moving components since they are not receiving appropriate oil for lubrication. If the oil filter becomes clogged due to engine sludge, it will drastically reduce the oil pressure at which the oil pump circulates the oil.

In some cases, the engine oil might not get to the cylinder head. Under this condition, it is best to pull out the engine, disassemble it, and thoroughly wash the engine parts with part washer solvents to avoid problems that may require total engine replacement.

Generally, if you have engine sludge, your O2 sensor will start malfunctioning and cause your engine to misfire, and you will notice reduce fuel economy. If you see these problems after having hard starting issues, it’s likely that you have engine sludge.

How to Clean Engine Oil Sludge

Getting oil out of your car is something you shouldn’t take lightly. So, I’ll share a technique so you could be able to continue to keep on top of getting and keeping sludge out of your engine. Grits in engine oil give you low oil pressure and tear down your engine. This technique is effortless to follow and will cost less than twelve bucks.  This will provide you with a crystal-clear picture of cleaning engine sludge with diesel. So, instead of purchasing an engine flush for this, you only need a few liters of diesel.

how to clean heavy sludge out of engine

Things Needed:

  • Oil catch pan
  • Socket wrench
  • Ratchet handle
  • Diesel
  • Funnel
  • Oil filter wrench
  • Quality engine oil
  • Oil filter
  • Mechanic layboard

Before we dive into the steps, if the sludge in your engine is not much or you are just concerned about your engine longevity, you don’t have to follow the below steps. All you have to do is purchase Liqui Moly 2037, add it to your engine oil, start the car, and run it on idle for 5 minutes. Then shut off the engine and do your regular oil change. It’s that simple.  If not, stick to the steps below.

Step 1. Park your car on a flat ground

When working under your car, one of the things you have to do is to park your vehicle on hard, level ground. Then, block off the rear wheels, so the car doesn’t move when you slide under. If you’re working in a garage, the garage pit will be the best place to carry out this flush.

Step 2. Jack up your car

After parking your car in a safe place, you have to jack it using a floor jack or hydraulic jack so you can easily slide under the car and carry out your work easily.

Step 3. Drain out the old oil

Grab your garage layboard and slide it under your vehicle. Place your oil catch pan directly under the engine sump. Take the right socket wrench and ratchet handle to lose the sump so the old oil will drain into the catch pan. After draining all the old oil, guide the sump by hand and snug it with your wrench. Remember to pour the old oil into a container and dispose of it later.

Step 4. Fill the engine with diesel or kerosene instead of motor oil

This is a critical step that you have to take. Ensure you pay close attention to this. Fill your engine with a mixture of diesel and engine oil. If your vehicle uses 5 liters of motor oil, you have to pour 4liters of diesel and a liter of motor oil. This is the best homemade engine flush, and it works effectively as an engine flush could.

Step 5. Start the engine and allow it to run

Next, start the engine and allow it to run at idle. Let it run for 5-10 minutes. Do not drive the car, do not engage the gears, and do not rev the engine as this can result in engine tear down between moving components. I recommend applying this step to older vehicles.

What if I’m using a newer car? You still have to utilize a mixture of diesel and motor oil, but you won’t have to start the vehicle after pouring the homemade flush, head over to your fuse box and remove the fuel pump relay, so it will not supply gas to the engine. There is more than one relay in the fuse box that looks like. You might need to visit your owner’s booklet to locate the fuel pump relay.

Try turning the ignition key to make sure the car doesn’t start. Now, crank the engine several times. You can do this up to 50-100 times. The reason for this is to prevent the engine from starting so it won’t cause damage to internal engine components. Mere cranking the engine will enable the oil pump to circulate the diesel around the engine and wash off the grits in it.

Step 6. Drain out the homemade flush

Take your oil catch pan and slide it under the vehicle. Place the catch pan directly under the sump so you won’t mess up the area. Unbolt the sump and allow the homemade flush to drain into the catch pan using the right tool you used earlier. Once the diesel is out, snug the sump by hand and torque down with a socket wrench.

Step 7. Replace the oil filter

The old oil filter had to be in place while performing the previous steps. Now, you have to take it off by loosening it with an oil filter wrench. Grab your new oil filter, feed it with quality engine oil until it’s half-filled and snug it by hand. Do not use an oil filter wrench while tightening it, but you have to make sure it’s well tightened by hand.

Step 8. Pour new quality motor oil into the engine

Get a recommended oil and pour in the engine, start the engine and let it run for 30 seconds, then turn it off and gauge the oil level.  Make sure the oil is gauged. Add Liqui Moly (20002). I usually add this product to my engine during every oil change. So, I recommend adding this product to your engine oil after a successful engine flush. Liqui Moly (20002) is a high-tech ceramic wear protection product; thus, it reduces friction and prevents metal-to-metal contact, which makes it the best product to use after flushing your engine. Watch this YouTube video for a visual presentation.


Q: Can you remove sludge out of an engine?

Yes. Taking out sludge from your engine is something you shouldn’t take for granted.  Ensure you flush your engine during oil change whenever you notice particles in your oil or sludge in the head cylinder.

Q: What is the best engine sludge remover?

Aside from the homemade engine sludge remover (a mixture of diesel and oil or kerosene and motor oil), the best engine sludge remover is Liqui Moly 2037, a highly effective detergent additive that cleans the interior engine before the flush. It is an overall sludge remover to flush your engine thoroughly and extends its longevity.

Q: How bad is engine sludge?

Is engine sludge bad? Engine oil sludge can cause catastrophic engine damage if overlooked for a very long time. When the engine oil clump together to form engine sludge, the oil pump will not properly circulate oil throughout the entire engine system to lubricate the moving parts. Suppose this happens; it will cause frictions and metal-to-metal contact resulting in expensive repair costs.

Q: Will synthetic oil clean sludge?

All modern motor oil has a percentage of solvent that will, to a lesser or greater extent, clean engine sludge, and some clean it better than others. That said, synthetic oil removes engine sludge to an extent. This doesn’t mean you won’t flush your engine when you notice oil sludge in your vehicle engine.

Q: Can frequent oil changes remove sludge?

A frequent or regular oil Change is a preventive measure to keep your engine far from sludge. However, if you have engine sludge already, the best option is to flush the engine and keep up with regular oil changes.

Final word

It’s no coincidence that one of the most overlooked engine problems can lead to expensive repair costs. For your car to run nice and smooth, several engine components have to work together, and if anything goes wrong, the whole system will be affected. Watching out and preventing engine sludge is a decision you won’t regret.

Watching out for engine oil sludge symptoms, doing a regular oil change, reading your service manual, and knowing how to clean engine sludge will help your engine run smoothly for a long time. Little preventive measures will save you from many engine problems in the future.

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Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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