Brand new oil is a relatively clear, free-flowing liquid that lubricates and protects the engine. But as it thickens into sludge it turns into a sticky hell stew that increases fricition and heat.

Common Causes of Oil Sludge

Sludge is caused by oil that has thickened by some means. That can be the result of poor maintenance, ventilation defects in the engine, or operating tempetures that are way too high. No matter the reason, the formula is the same.

More friction → more heat → more sludge → more friction → more heat → more sludge.

Common signs of sludge include a loss of oil pressure, higher engine temperatures, rough acceleration, poor gas mileage and scornful looks from your mechanic.

Poor Maintenance Habits

A crankcase filled with sludge
A sludged-up crancase shows how extreme the problem can get

The most obvious cause of sludge is a neglectful owner. Poor oil change habits will lead to the oil oxidizing in the engine. As oil roams through the engine, additives in the oil absorb soot, dirt, water, metallic particles, excess fuel, and anything else that keep the engine from running efficiently. Oil starts to thicken once it reaches its absortion capacity.

While it's important to know your oil's lifespan and how long it's been in the engine, it's also important to pay attention to your engine's specific consumption habits.

We’re not interested in cases of neglect. The more concerning causes of oil sludge have to do with defects in the engine.

Crankcase Ventilation System Defect

Oil sludge can be the result of a poorly designed or defective crankcase ventilation system, like the one found in the 1998–2005 DaimlerChrysler’s 2.7L engine. This engine is notorious for allowing hydrocarbons to enter the oil and break down the additives that help gather all the gunk.

Additionally, water pump gasket failures have been known to leak coolant into the oil. And all those extra contaminates can severely degrade the oil’s life.

These issues have caused an incredible amount of sludgy complaints from owners of the Concorde, Sebring, Intrepid and Stratus.

Engine Operating Temperature

Oil oxidizes the most when the engine’s operating temperature is too high. The oxidation only gets worse when that heat lasts a long time.

Volkswagen’s 1.8L turbocharged engines have a history of sludge-related complaints. From 1997-2005 their turbocharged engines came equipped with a tiny 3.7-quart oil capacity. And mechanics say it doesn’t provide the engine enough oil to dissipate the heat and it removes all margin of error for owners who may be a little late on their oil change.