How to Paint an Engine Block? The Devil Is in the Details!

You want your engine to look as powerful as it runs, right? For most gearheads, that’s the real joy of building, driving, racing, or simply owning a high-performance machine — popping the hood and showing off a gleaming powerplant. But achieving that clean, professional look isn’t as simple as grabbing a spray can and going wild in the driveway.

Here’s the good and the bad news: painting an engine is far easier and cheaper than painting your car’s exterior panels, and it’s a project you can absolutely tackle at home. However, just like a full-body paint job, the details matter — a lot. Cut corners and you’ll end up with a sloppy finish or, worse, create future problems you’ll regret.

We’re currently building a 1,000-plus horsepower 392ci Chrysler third-gen Hemi, but the techniques we’re using to paint the block work on virtually any engine — whether it’s an aluminum or iron V8 from Mopar, Ford, or Chevy, or even a four- or six-cylinder.

We chose to paint our Hemi at the short-block stage — after the bottom end was assembled but before the rest of the engine came together. This is the ideal time because it’s easier to mask off parts, and the paint won’t get scratched or damaged during assembly. Of course, you should never paint a block before it’s been cleaned, inspected, and machined.

If you’re planning to paint aluminum components like the intake manifold, cylinder heads, or water pump for a more stealthy look, you may want to wait until later in the build. In our case, we decided to leave the aluminum unpainted, so painting at the short-block stage was the perfect move.

If you want your engine’s paint job to last for years — and look as good as it performs — proper preparation is absolutely essential before you even think about spraying. There are two main ways to approach this step:

1. DIY Prep: Take a chance with a block of unknown condition, inspect it as thoroughly as possible on your own, then clean and paint it.

2. Professional Prep: Bring the block to a machine shop for a full inspection and professional cleaning.

The second option is especially important if you’re building a high-horsepower engine. The more power you plan to make, the more time, effort, and money you should invest in prep work. That means procedures like:

• Hot-tank cleaning: Immersing the block in a heated solution to remove oil, grime, rust, and old paint.

• Sonic testing: Measuring cylinder wall thickness to ensure structural integrity. For older blocks, you want at least 0.120-inch wall thickness.

• Magnafluxing: Using magnetic particles to check for hidden cracks that could lead to catastrophic engine failure.

When it comes to hot-tank cleaning, you’ll typically have two options: a mild detergent bath or a caustic soda solution. If you’re planning to reuse your cam bearings — as we did — opt for the mild, non-sudsing detergent bath. It’s less aggressive and won’t damage sensitive components.

This upfront work might seem tedious, but it’s the foundation of a strong, long-lasting engine build — and a flawless, professional-looking paint job.

Once your block comes back from hot-tank cleaning, the prep work isn’t quite done yet. Mount it securely on a sturdy engine stand and take the time to thoroughly inspect and clean every surface again. Any leftover grime or hardened debris hiding in tight corners — especially around gussets, oil pan rails, and casting crevices — will become even more visible once paint is applied, ruining the finish and potentially causing adhesion issues.

To tackle this, grab a few cans of non-chlorinated parts cleaner or brake cleaner when you pick up your engine primer and paint. Spray the cleaner into those hard-to-reach areas and wipe away any remaining residue. This final pass ensures the surface is completely clean and ready to accept primer and paint.

For example, in our build at IMM Engines in Indio, California, engine specialist Johnny Wadlund gave the 392ci Hemi BGE block one last thorough cleaning, using parts cleaner to flush out dirt and oil buildup along the pan rail edges. This step might seem small, but it’s crucial for achieving a smooth, professional-looking finish that will stand the test of time.

People often look for shortcuts when it comes to painting an engine, and one of the most common questions is: “Can I paint the engine without removing it from the car?” The short answer: absolutely not.

There’s simply no way to properly mask off all the areas that shouldn’t be painted while the engine is still in the vehicle. Even after removing a modern fuel-injected engine from the car, you’ll notice how many components remain attached — and that’s before dealing with all the hoses, wiring, sensors, and accessories that clutter the engine bay. Attempting to paint an engine that’s still installed will almost always lead to overspray, uneven coverage, and a messy finish.

If you want a clean, professional-looking result, the engine needs to be at least partially disassembled — or more accurately, partially assembled — before painting. This approach gives you full access to critical surfaces, allows for proper masking and surface preparation, and greatly reduces the risk of having to strip and redo the job later. In short, doing it the right way from the start will save you time, money, and frustration.

If you’ve decided it’s time to give your engine a fresh coat of color, the first thing to understand is that not all spray paints are created equal. You need a high-temperature engine enamel designed to handle the extreme conditions under the hood — especially the heat, oil, fuel, and chemical exposure that a typical spray paint simply can’t withstand.

Take Dupli-Color’s engine enamel, for example. According to the company, it’s formulated with ceramic resins that help with heat dissipation and gloss retention, while also protecting against blistering, flaking, cracking, and peeling even after repeated exposure to high temperatures and harsh automotive fluids. It’s built for the demands of race cars, street rods, and restoration projects, and can withstand temperatures up to 500°F intermittently — more than enough for most engine blocks.

As for how much paint you’ll need, the answer is pleasantly simple. Unless you’re working with something massive — say, a marine engine for a yacht — you’ll typically only require one can of primer and one can of color coat to get the job done. That’s enough to deliver a durable, high-gloss finish that will make your engine bay look as good as it performs.

For our 392ci Hemi project, the total cost to paint the engine was surprisingly affordable — and even cheaper if you’re willing to put in a bit of elbow grease yourself. Here’s the full breakdown:

• Dupli-Color Primer (DE1612): 1 can – $13.99

• Dupli-Color Chrysler Hemi Orange (DE1652): 2 cans – $27.98 (but we only needed one can, applying two coats, so the cost could’ve been just $13.99)

• Non-chlorinated parts cleaner (Summit SUM-941241): $4.99

• 3M “Frog” masking tape (TES-7000048805): $11.99

• Disposable utility knife blades (WMR-W744): $1.99

• Hot-tank block cleaning (IMM Engines, Indio, CA): $100

✅ Total cost: $146.95
💡 DIY savings: If you only use one can of color coat, that drops to $132.96.

Alternatively, if you prefer to leave the job to the pros, IMM Engines offers a full prep, mask, and paint service for $200 — a pretty fair deal considering it takes about three hours of hands-on labor to get the block cleaned, masked, and painted properly.

Either way, painting your engine isn’t expensive — and with careful prep and the right products, the result is a professional-looking finish that will last for years.

As we mentioned earlier, when it comes to painting an engine, the devil truly is in the details. Engine blocks have numerous precision-machined surfaces that must be kept free of paint and overspray — including gasket sealing areas, threaded holes, motor mounts, and other sensitive surfaces. If paint gets on these spots, it can cause sealing issues, assembly problems, or even mechanical failure.

To avoid that, carefully mask off these areas with 2-inch-wide green masking tape. Most enthusiasts refer to this as “frog tape” because of its color, though FrogTape is actually a brand name known for producing crisp paint edges and strong adhesion. Before applying the tape, make sure all surfaces are clean, dry, and free of oil or debris so the tape sticks properly.

You don’t need to fully cover large openings like the cylinder bores, crankcase opening, bellhousing flange, or timing-chain access area. Instead, use a masking board cut from a piece of cardboard to shield those larger sections while you paint. Just be sure the edges near painted areas are well-taped — this will give you clean lines and prevent overspray from reaching places it shouldn’t.

Of all the steps in painting an engine block, masking and trimming is the one that demands the most patience — and it’s also the step that has the biggest impact on both the final look and the engine’s functionality. Proper masking ensures a crisp, professional finish and protects critical surfaces from unwanted paint.

The goal here is to carefully trim away any excess tape along the edges of the block. Use the edge of a razor blade to gently scrape the tape rather than cutting with the tip — this reduces the risk of scratching the metal or damaging sealing surfaces. Green “frog” tape works particularly well for this step because it creates sharp, clean paint lines and forms a tight seal that prevents paint from seeping underneath.

Because you’ll be scraping rather than slicing, razor blades will dull quickly, so treat them as disposable. It’s a good idea to start with a fresh pack — for example, a set of five blades costs about $1.99 from Summit, and similar options are available at most hardware stores.

As you’ll see in our video, trimming the paint mask is a detailed and time-consuming process, but it’s worth every minute. A precise mask job will not only give your engine a professional, show-quality finish but also protect vital areas for proper sealing and assembly.

The 392ci Hemi block — like most modern fuel-injected V-8 engines — has numerous precision-machined areas that must be carefully masked before painting. In addition to obvious spots like the oil pan rail and timing cover sealing surface shown here, there are more than a dozen other machined areas that require protection from paint overspray.

A good rule of thumb: If you’re unsure whether a surface, dowel, or bolt hole needs masking, go ahead and cover it. It’s always better to spend a little extra time taping off these areas now than to risk paint interfering with proper gasket sealing, alignment, or component installation later.

If you’ve prepped everything correctly, the painting itself is the most enjoyable part of the job, and it all begins with the primer coat. Don’t be tempted to skip it — primer is essential for helping the paint bond properly, last longer, and deliver a uniform color finish. It also provides an extra layer of protection against heat, fluids, and harsh chemicals.

Before you start, grab a thick, rectangular piece of cardboard roughly the length of your engine. This will act as a handheld shield to protect sensitive components like the cylinder bores, pistons, crankshaft, rods, and timing chain from overspray.

When applying primer:

• Shake the can well to mix the contents thoroughly.

• Hold it 12 to 18 inches from the surface.

• Spray only while moving the can smoothly and evenly across the block.

Avoid stopping or pausing over one spot, as this can lead to paint drips and runs — an easy mistake that can ruin an otherwise professional-looking finish.

For those who care about authentic color accuracy — and many hot-rodders do — it’s worth noting that not all “orange” engine paints are created equal. Chrysler Orange and Chrysler Hemi Orange, for example, are distinctly different shades. Chrysler Orange is slightly darker and more muted, leaning toward a pastel tone, while Chrysler Hemi Orange is brighter and more vibrant — in fact, it’s the most vivid of all the orange engine paints Dupli-Color offers.

Chevy Orange, on the other hand, has a whiter, more pastel base and a redder hue than either of the Chrysler colors. To make things even more interesting, there are two versions: Chevy Orange and Chevy Orange-Red — the latter being almost a tomato-red shade.

Because these differences can be subtle in the can but obvious on the engine, always spray a test patch on a piece of cardboard before committing. This not only lets you confirm the exact shade but also ensures you’ve shaken the can thoroughly for an even, accurate color.

Peeling off the masking tape after laying down the final color coat is one of the most satisfying moments in the whole process. The key is timing — you want to remove the tape while the paint is still slightly tacky. If you wait until it’s fully dry, the hardened paint can crack or lift along the edges as you pull the tape away, ruining that crisp, clean line you worked so hard to create.

Most engine enamels dry to the touch in about an hour, and once that time has passed, your freshly painted block will be ready for final assembly.