9 Things You Should Know About Engine Sludge

Oil sludge is a murderous foe that looks a lot like a burnt marshmallow. If you love toasted marshmallows but don’t have the patience to toast them (or if, like me, you like them burned), you’re probably familiar with the black, bubbly surface that develops once the marshmallow is on fire. Blow it out, let it cool a bit, and enjoy! Yum, right?

That’s fine if you’re at a cookout, but burnt-marshmallow oil is less of a treat. A marshmallow engine is a bad sign. It means your oil has broken down due to heat and time and is no longer protecting your engine. Much like a marshmallow settles directly on your love handles, your oil, too, becomes a traitor. It joins the dark side and starts causing damage to your vehicle.

9 things you should know about this car killer:

1. Dirty oil isn’t necessarily bad oil.

Oil sludge is often thought of as just “dirty oil” but that’s not the whole story. Oil is supposed to get dirty. It travels around your engine, lubricating the metal components that have to slide past each other smoothly. If the oil finds contaminants like metal shavings, dirt and water, it absorbs them and runs them through a filter. When it’s working right, engine oil gets its hands dirty (if it had hands).

2. Sludged oil eventually fails.

Over time, exposure to heat and other debris cause oxidation, which is a change at the molecular level. Instead of becoming slippery, oil gets sticky or tacky. (Burnt marshmallow, remember?) Contaminants stick with the oil and clog up your filter. The oil also loses its ability to tolerate heat and starts to burn onto the components it’s supposed to be protecting.

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3. Sludge kills the engine.

The components in your engine are designed to slide smoothly by each other to generate enough pressure to power your vehicle. Evil sludge attaches itself to any hot metal surface. These components now start to rub. The sludge has turned the vital moving parts against each other!

sludge kills engine

The oil’s pathways in the engine are extremely small. In fact, some are so small they’re now referred to as “micro passageways.” With sludge clogging the moving components, these micro passageways become nearly nonexistent passageways. If oil is not getting to the critical parts it’s designed to protect, engine components will suffer, catastrophically.

At this point, you’ll start to notice changes in how your car drives. It may feel like it’s running “rough.” Why? More heat=more friction=more damage to the oil and the engine.

4. Sludge is bubbly and rough.

Chemistry snippet: It’s important to know that all oils are loaded with potential carbon-based energy. When they burn, this potential energy leaves behind carbon deposits.

Ever spilled butter on your stovetop? (Mmmmm… butter.) The black tarry stuff that’s left behind is sludge! It doesn’t burn smooth and flat. When it burns, it leaves behind a bubbly, rough surface just like our burnt marshmallow. And if you keep exposing it to heat, it will just get harder to clean off of your stove.

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5. Synthetic oil is a good choice but won’t necessarily save you.

Synthetic oils are at less risk of temperature damage than conventional oils. For drivers in extremely cold climates, synthetic oil helps your car start more consistently. It also reduces the wear that occurs once your very cold engine is running.

Synthetic oils also have a much lower evaporation rate than conventional oils. If you do a lot of stop-and-go driving, the heat inside your engine increases. Synthetic oil provides greater protection against extreme heat for a longer period of time.

Yes, synthetic oil is good, but it’s not a magic cure for oil sludge. Synthetic engine oil is still oil. And while a synthetic oil habit is great for a brand-new car, your old faithful may already be facing sludge damage. Now what? How can you clean up an already sludged engine? Or is it too late?

6. You can clean up an already sludged engine.


Varnish and sludge are tough. And breaking up the varnish that’s already deposited on your engine takes some intensive cleaning and lubrication. First, you need BG EPR® Engine Performance Restoration®. And second, you need heat; a running engine offers that. BG EPR® works its way through your engine, softening existing deposits and dissolving them so they can be filtered away.

7. You can prevent more sludge.

Enter additives. Still not magic, but definitely a preventive measure.


Additives can help in many ways! An oil additive like BG Advanced Formula MOA® is a great choice to fortify your oil and boost its ability to tolerate heat and pressure. This is especially important if you drive a classic car, like the muscle cars built before 1975. However, even new cars can use an extra boost of antioxidant and wear protection. BG Advanced Formula MOA® keeps your engine well-lubricated to reduce wear and helps prevent the sludgy deposits that cause future damage.

8. Sludge buildup is expensive.

Sludge buildup doesn’t just cost you money when the engine gives out. Every sticky bit of varnish costs your engine in efficiency and power. It can also add to your fuel expense. If you notice a loss of power or that you need to fill up more often to do the same amount of driving, sludge might be impacting your vehicle and your wallet. It’s time to do something about it.

9. Engine sludge kills cars. 

A badly sludged engine can ultimately become a failed engine, and engine replacements aren’t cheap. In fact, it’s often easier to get a loan for a new car than it is to afford the engine repairs caused by sludge.

BG protects more than just your engine oil. We offer the Lifetime BG Protection Plan®, built to protect your car from engine to transmission and radiator to brakes. Our goal is to keep the car you’ve got running smoothly for as long as possible.

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Irreversible damage from engine sludge can be stopped!

Michael Belluomo, BG Technical Service Manager

By Michael Belluomo
BG Technical Service Manager
Mike has been with BG for 23 years. He manages all product-related inquires and assists with BGU and Distributor-specific training. He is a regular contributor of articles on product understanding and technical industry trends.

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