How to Test an Engine Block for Cracks: Wet Magnaflux Testing Explained by Automotive Machining Experts

“What is Wet Magnaflux testing?” It is a special type of diagnosis we use on engine blocks and cylinder heads.

In this blog, you’ll learn about the causes and signs of a cracked engine block. We’ll also explain Wet Magnaflux testing and how it can give you peace of mind with a definitive diagnosis. Once you know for sure if the engine block is your issue, you and your mechanic can formulate a plan for repair, including state-of-the-art machining techniques to get you back on the road again.

Photo by Garett Mizunaka on Unsplash

What Is a Cracked Engine Block?

The engine block is the bottom part of your engine, usually made of cast iron or aluminum. It’s the structure on which many other engine components are built, including the cylinder heads, pistons, connecting rods, and crankshaft.

A crack in the engine block is exactly what it sounds like. The integrity of the block is compromised, often by hairline cracks that are hard to see with the naked eye.

What Are Common Signs of a Cracked Engine Block?

Just because a cracked engine block isn’t visible doesn’t mean your engine won’t notice it. Cracked engine block symptoms include:

  • White smoke resembling steam coming from the exhaust
  • Engine overheating
  • Leaking engine oil or coolant
  • Coolant and oil mixing
  • Bubbles in the coolant from combustion gases
  • Engine misfiring and rough running
  • Warning lights on the dash — check engine, high temperature, low coolant

You may also experience problems with the cylinder heads before or concurrent with a cracked engine block. In fact, these two problems are often hard to tell apart, which is why a precise diagnosis is so important (see more below).

You don’t want to drive with a cracked engine block, as you can do more damage to the engine. You could also find yourself stranded far from home or cause an accident if your vehicle breaks down on the highway. If you suspect your engine block is cracked, it’s advisable to have the vehicle towed to your mechanic.

What Causes a Cracked Engine Block?

The number one cause of a cracked engine block is overheating. Another frequent contributor is freezing temperatures when there is not enough antifreeze and too much water in the vehicle. The expanding water can eventually crack the engine block as it freezes.

Occasionally, design and fabrication issues also cause cracked engine blocks. Honda, in particular, had to issue a recall for some of their Civics with this issue.

How Is Magnaflux Testing Used to Diagnose a Cracked Engine Block?

As mentioned above, it’s vital to know if you indeed have a cracked engine block or if something else is causing symptoms. That’s why high-tech diagnosis can be so helpful. Even when we can’t see a crack in the block, today’s tools let us find the smallest fractures.

Wet Magnaflux testing (sometimes called “Magnafluxing”) is the gold standard, and it can save vehicle owners both time and money by narrowing down a diagnosis quickly and reliably. This is especially important for people who rely on their trucks for business, where every day without transportation can cost thousands in revenue.

How does Wet Magnaflux work? It uses tiny fluorescent iron oxide particles within a strong magnetic field to detect breaches in the engine block. It leverages the magnetic field on the surface of the block, which is sprayed with iron powder encapsulated in a fluorescent pigment. The iron powder remains contained in place by a water or oil bath on the area as it seeps into any cracks or crevices. It can be visualized with a black light tool that detects fluorescence, allowing mechanics to see cracks that would otherwise be invisible.

Wet Magnaflux testing can also be utilized on cylinder heads and other iron alloys where the naked eye just can’t see cracks, dents, or leaks. For non-iron-based metals, like aluminum (not magnetic), there are other processes available, such as the use of penetrative dyes, ultrasonic testing, pressure testing, and vacuum testing.

Can You Fix a Cracked Engine Block?

Once you know for certain that you’re dealing with a cracked engine block, the next step is to decide with your mechanic if it can be repaired and if it’s worth it. There is the possibility of a welding, stitching, or sealing repair based on the size and location of the crack. However, in other instances, an engine replacement may be the best choice. The decision will depend on the extent of the damage, the value and lifespan of the vehicle, and your budget.

Fortunately, if the problem turns out to be a cracked head gasket, a cracked cylinder head, or a problem with the cylinder itself, an automotive machining expert can offer you many options for repair. The key is to partner with a professional who has experience and success with engine rebuilding for the best possible outcome.