How to Clean the Inside of an Engine? – A Detailed Guide

Written by

Bruce Sonnier


Marcus Dutton

how to clean the inside of an engine

Car maintenance shouldn’t just be as superficial as keeping your car looking clean and good on the surface. You also have to clean its internal engine parts to prevent the buildup of sludge, grease, dirt, rust, etc.

In this article, you’ll learn how to clean the inside of an engine in two ways. Both are crucial for keeping your car in optimum condition and preventing malfunctions and damages to the components of the engine.

Step-by-Step Guide


Cleaning a car engine internally would mean cleaning the engine block or doing an engine flush or both, depending on your cleaning needs.

An engine block needs to be cleaned for your car’s motor to work efficiently, while an engine flush is necessary to get rid of all sorts of deposits before lubricating the engine components with a new, clean oil.

Method 1: Clean Engine Block While in Car

What to Prepare:

  • Plastic
  • Electrical tape
  • Wire-bristle brush/scraper
  • Stiff-bristled brush
  • Brake cleaner
  • Degreaser or laundry soap and hot water
  • Water
  • Soft rags
  • Small brushes
  • Hose with nozzles
  • Drain pan
  • Air compressor
  • Lubricating oil
  • UV leak detector

Step 1: Disconnect the Battery Cables

When you’re going to clean inside of an engine block, you first need to take the precautionary measure of disconnecting the battery cables. The negative battery cable must be disconnected first followed by the positive cable to prevent a short circuit.

Step 2: Protect the Electrical Parts

Another necessary precautionary measure is to protect the delicate electrical parts such as the plug wires, ignition coils, fuse box, etc. This will help prevent causing any damage to them and keep you from getting electrocuted.

Step 3: Clean off Encrusted Dirt, Oil, and Grease


If you notice any caked-on dirt, oil, and grease, scrub them off with a wire-bristled brush or stiff-bristled brush. Or you can also use a scraper.

Applying a brake cleaner onto the lifter bores, cylinder bores, oil galleys, and freeze plug holes would also help get rid of buildup.

Step 4: Clean the Engine Block With Degreaser

Cover the entire engine block with the degreaser. Then let it soak the engine block for a few minutes as instructed on the product label to loosen the contaminants. Finally, scrub them off with a stiff-bristled brush.

Note: If you don’t have a degreaser, you can use laundry soap and hot water for engine block cleaning.

Another option: Cleaning Car Engine Without Water in 7 Easy and Safe Steps

Step 5: Rinse the Engine Block


Thoroughly rinse the engine block. Avoid spraying water at high pressure on the engine block but rather, use a regular hose with nozzles to efficiently clean car engine inside without piercing or detaching parts of the engine.

Moreover, collect the wastewater from cleaning your engine block and properly discard it according to your local laws.

Step 6: Spray Lubricating Oil on the Engine Block


Spray a protective coat of lubricating oil on every surface of the engine block, inside and outside. That would help prevent it from rusting.

Step 7: Dry the Engine Block and Re-apply Lubricating Oil


Thoroughly dry both the inside and outside of the engine block before assembly of the battery cables back onto the car’s battery. Use an air compressor to dry it, and then re-apply lubricating oil afterwards.

Step 8: Check the Engine for Leaks

You should also make sure that there aren’t any leakages from the engine. You can check by using a U/V leak detector kit.

You can directly pour the leak detector dye into the engine. Or if your car’s engine needs oil refilling, mix it with the oil you’ll refill the engine with.

Then let the engine run for 5 to 10 minutes.

Afterwards, cool down the engine and shine the UV light around it to search for leaks. If you find a glowing green spot, it means there’s a leak there.

Method 2: Doing an Engine Flush

What to Prepare:

  • Car jack or drive-on ramps
  • Ratchet and socket set
  • Engine flush
  • Drain pan
  • Oil filter
  • New engine oil
  • Rag
  • U/V leak detector kit

Step 1: Prepare for Engine Flushing


There are a couple of things you need to do before flushing an engine. These tasks will make cleaning easier for you.

The first task is to run the engine and bring it to the fullest operating temperature.

Then elevate your car by using a car jack or drive-on ramps. This will help you move and see better as you work from underneath your car later.

Step 2: Add in the Engine Flush

Flushing an engine can be done without water but would require the use of an engine flush. First, turn off the engine, then pour the engine flush into it.

Then, run the engine for a couple of minutes depending on how contaminated your engine is. You can leave it running for around 10 to 15 minutes and proceed to change the oil after.

Step 3: Drain the Engine Oil


You must do the oil change while your car’s engine is still hot. This will let the oil flow more easily.

Take the drain plug out to let the oil drain flow onto the drain pan. In some vehicles, you need to remove the belly pan to get the drain plug, while for others, there’s no need to do this.

Next, replace the oil filter. If the vehicle uses a cartridge oil filter, you can replace it while draining the oil.

Step 4: Refill the Engine With Engine Oil


Reinstall the drain plug. Then refill your car’s engine oil following the specified amount for your vehicle.

Step 5: Check for Any Leakage in the Engine

After refilling the engine, check it for leaks with the use of a U/V leak detector kit. The instructions for this are identical to what we have described above.

When you’re all done with the cleaning and checking, reinstall the belly pan.


Neglected internal engine components can cause problems for you in the future. So do yourself a favor and practice these steps on how to clean the inside of an engine for your regular car maintenance.

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