Skip the auto shop - Our mechanics make house calls

How to Prevent Motor Oil Sludge

dirty motor oil

New, unused engine or motor oil is a clear, easily flowing liquid that combines base stock and a collection of additives. These additives can hold soot particles and maintain the consistency of the engine oil. Engine oil lubricates the moving parts of the car and in this way, not only reduces friction but also helps to keep the engine cool. With frequent use, the motor oil accumulates coolant, dirt, water, fuel and other contaminants. It also breaks down or oxidizes because of the intense heat of the internal combustion engine of your car. As a result, it turns into sludge or a thick gel-like fluid that can cause serious damage to your engine.

How motor oil works

Engine or motor oil can be either conventional or synthetic. It works to absorb and protect your engine from contaminants. Over time, however, it reaches its capacity of absorption and instead of carrying away contaminants, deposits them on the engine surfaces and in all the other parts where it circulates. Instead of lubricating and reducing friction, the oxidized sludge causes a buildup of heat in the engine. Motor oil functions as a coolant to some extent, but oxidized sludge acts as the opposite. You’ll notice that the oil pressure is falling, and you get lower mileage per gallon.

Motor oil sludge first develops on the top of the engine, the valve cover section, and in the oil pan. Next, it blocks the oil screen siphon and stops oil from circulating in the engine leading to more damage with every stroke. Aside from severe engine damage, you also risk damaging the gaskets, timing belt, radiator and cooling systems of the car. Ultimately, the engine could stall completely.

Common reasons for engine oil sludge buildup

  • Engine oil is unstable and tends to oxidize when exposed to oxygen under conditions of high temperature. Oxidation can occur faster if the engine oil is heated over extended time periods.

  • During oxidation, the molecules of engine oil break down and the resultant products combine with the dirt in carbon form, metallic particles, fuel, gases, water and liquid coolant. Together the mixture forms a sticky sludge.

  • Stop-and-go driving in heavy traffic conditions and in areas where there are lots of traffic lights can contribute to sludge buildup. Frequently driving over short distances can also cause sludge.

Keep in mind

  • When you turn the ignition on, check the dashboard for the Check Engine Light and the Oil Change notification light. Both could indicate that the motor oil needs replacing.

  • Study the owner’s manual that your car manufacturer provides for instructions on when to replace the motor oil. Typically, manufacturers give you the mileage increments in which to replace the engine oil. Book an appointment with your mechanic accordingly.

  • Avoid stop-and-go driving as far as possible. Walk or bike over short distances to prevent motor oil sludge buildup.

  • If the dashboard gauge shows that the car is heating up, have your mechanic check for motor oil sludge also.

  • It is never advisable to add engine oil if you see that the oil pressure is low. If the oil pressure light is on have it inspected or replace it completely.

How it’s done

Your mechanic will check the engine for signs of a sludge accumulation and let you know if the motor oil needs replacing. He or she may also check for the other possible reasons why the Check Engine Light is on.

What to expect

A top-rated mobile mechanic will come to your home or office to determine the cause of the various signs of motor oil sludge. He or she will then provide a detailed inspection report that covers the part of the engine worst affected by the motor oil sludge and the cost of the necessary repairs.

How important is this service

Make sure you follow your owner’s instructions manual and have your mechanic replace the motor oil regularly. It is essential that you do this or you risk severe damage to your engine. You might even have to replace the entire engine and that can prove to be very expensive repair work.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
Veteran and Military Driver Laws and Benefits in Idaho
The state of Idaho offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch in the...

Related questions

Q: Alarm for oil change keeps going off - 2009 Dodge Sprinter 3500

Hold the trip reset for ten seconds to clear it. This should clear it. Otherwise, try holding the trip reset and turn on the key and hold it until the oil indicator goes out. If the problem is not going...

Q: Oil filter housing turns with filter.

I would get a strap wrench and try to hold the housing with it while loosening the filter cap. Sometimes these caps are hard to remove. If you are still having trouble, a certified technician, like one from YourMechanic, will...

Q: Exhaust smoke smells like gas or burning oil.

Hi there. The smoke coming out of your exhaust is most likely oil being burned through your engine. The oil gets into the cylinder by a few ways. The first way is for the oil to get by the oil...