The Best Ways to Clean an Engine Block Before Doing a Gasket Change

There's really no right or wrong way to clean an engine block before changing a gasket, and to the extent that there is it depends upon the engine and which gasket you're replacing on it. Replacing a throttle body gasket on a fresh engine isn't going to require nearly the prep work that a grungy old oil pan will. Just use your discretion, and choose the method that works best given your time and budget restrictions.

Scraping and Brushing

Most types of engine cleaning involve some good old fashioned elbow grease. Every bit of built-up grease that you can remove by scraping it off with a gasket scraper or removing it with a wire brush is that much less that you'll have to dissolve with a solvent or wash free later. It's a dirty job, but relying on nothing but chemicals and pressure washing will make for more of a mess later. Just go around your target area with a probe and look for anything that you can remove manually.

Paint Brush and Soap

A natural-hair paint brush and dish detergent will work under most circumstances, and isn't likely to damage anything around the target area. You can increase the efficacy of this method by using the hottest possible water, near-boiling if possible. If you're going to be at it for a while, then keeping your cleaning solution on a hot plate will help. Just bear in mind that any kind of detergent or soap will effectively lower the boiling point of your solution, causing it to foam up and overflow if it gets any hotter than a low simmer.

Chemicals and Wire Brushes

Sometimes soap and water simply won't cut it, and that's when you might want to look into more aggressive methods. Gasoline, kerosene, diesel fuel, paint thinner and acetone will all dissolve stuck-on grime, but they're messy, they stink and pose fire and environmental hazards. This is especially true during cleanup; at some point you're going to have to rinse the stuff out with soap and water, and then where is it going to go? All of these solvents kill grass and contaminate groundwater, and engine grunge in the solution will easily stain your driveway. This last goes for specialized engine degreasers as well.

Pressure Washing

This is the method of choice if you have the engine out of the car, but probably isn't such a great idea otherwise. Even if you cover the wheel wells and electronics with a tarp, the water and cleaning solution is going to go everywhere. Pressure cleaning is a more viable option if you're changing an oil pan gasket, since the bottom of the engine is fairly well-insulated against water intrusion. If you have an old carbureted engine, you might be able to get away with pressure washing if you tightly wrap the distributor, alternator, starter solenoid, ignition coil and other electronics with some packing cellophane.

Hot Tanking

This is by far the best method if you're doing a full rebuild, but isn't an option unless you do a complete teardown and disassembly. Hot tanking involves dropping the entire engine block into a vat of near-boiling cleaner, and will get the inside and outside of the block cleaner than it was since it was cast. This isn't something you can do at home; only machine shops have the equipment necessary to properly hot tank an engine.