Signs Of A Cracked Engine Block

Do you suspect that your car has a cracked engine block? What are the symptoms of a cracked engine block and the repair or replacement cost? Here's a guide.

Unfortunately, a cracked engine block is a rare but generally pretty tricky situation. You want to avoid it at all costs by carefully looking after your car at all times.

Signs of a cracked engine block include overheating, poor performance, oil and coolant leaks, and evidence of these two liquids mixing.

What should you do if you find an engine block crack or suspect your vehicle has one? Will it make any difference to performance? How much does it cost to repair? And is it safe?

I will answer all these questions in this guide. Without further ado, let’s delve into it.

Note: Just noticing one of these symptoms doesn’t necessarily mean you have a cracked engine block. Other underlying causes are possible (and usually more likely).

Table of ContentsShow

What Is An Engine Block?

Auto mechanic adjusting cylinder head on engine block at workshop.

You don’t have to be a trained auto mechanic to know that a cracked engine block isn’t good. But how do you spot the signs?

First, it’s essential to know what an engine block is. An engine block is a large piece of molded metal housing the cylinders, pistons, con-rods, and crankshaft.

It’s the big, heavy, chunky part of the engine.

You’ll see the cylinder head when you open your car’s hood and remove any covers. This is bolted onto the top of the main engine block and contains the valves, spark plugs, intake and exhaust inlets, and the camshaft(s) in most configurations.

The engine block is underneath this. The head gasket sits between the two to ensure a perfect seal.

Both it and the cylinder head contain channels for oil and coolant to lubricate, cool, and clean the system consistently. They pass these liquids between the block and the head through carefully engineered holes in the head gasket.

Basically, an engine block is the sort of tough outer shell guarding the sensitive, carefully-tuned process happening within.

Why Does An Engine Block Crack?

Cracked Engine Block
Example of a cracked engine block.

When we say an engine block has “cracked,” we usually refer to either the outside of the block or the channels carrying oil and coolant.

These develop hairline cracks and usually lead to oil and coolant leaking or mixing.

Engine blocks tend to crack as a result of our old friend overheating. When the stress of expanding metal becomes too great for the block to handle, cracks will inevitably form.

Coolant and oil levels must be regularly checked and topped up, if necessary. This will keep the engine cool, lubricated, and free from sludge, all of which prevent overheating.

Note: Some use the term “cracked engine block” to mean a cracked cylinder wall. The cylinders are technically part of the engine block, so this makes perfect sense. However, it’s more commonly referred to as a “cracked cylinder wall”. This is an even more severe problem. However, this guide will focus mainly on cracks in the block that don’t directly affect cylinder compression.

Signs Of A Cracked Engine Block

Cracked Engine Block Symptoms

As mentioned, overheating is almost always what causes cracked engine blocks. Thankfully, overheating is straightforward to spot using the dashboard indicator gauge.

Here are several things, including overheating, for you to watch out for.

Remember that these symptoms alone don’t necessarily indicate a cracked engine block, but they might. There’s no possible online substitute for a skilled mechanic’s in-person diagnosis of your issue.

If you notice these symptoms, drive slowly to an auto shop. If possible, call a mechanic out to your home or workplace instead.


Temperature Gauge Goes Up And Down While Driving

The engine temperature gauge on your dashboard is connected to the coolant temperature sensor (CTS or ECTS). It’s always crucial to keep an eye on it while driving.

Under normal circumstances, the needle shouldn’t show a rise in temperature until the engine has time to warm up. In summer, this might be within a couple of minutes. In harsh winters, it could take ten minutes of driving time.

Most engines run between 85 and 100 degrees Celsius (185 to 212 degrees Fahrenheit). Anything considered “too hot” for your motor will be shown as the red range on the gauge.

If you see the needle moving towards this part, your engine is getting too hot. Stop and turn off the car to let it cool down.

The head gasket, coolant, and oil are the most common culprits for overheating engines.

Coolant Issues

How To Put Coolant (Antifreeze) In Your Car

Coolant can leak from various points in the system: the rubber hoses, the clamps, the water pump, and the radiator are some of the most common. Leaks could also occur inside the engine block or through cracks.

If the coolant level is low (check it by looking at the header tank when the engine’s cool), top it up with the right kind of coolant. When you next run your car, see if the temperature continues to rise. If it does, you have a bigger underlying problem.

Low Oil Levels Or Dirty Oil

Car Service Oil

Motor oil has the job of lubricating the metal parts within the engine. This keeps them slick and prevents them from building up friction – in other words, heat.

As a result, all the relevant parts shouldn’t expand beyond their expected limits.

If the oil level is too low, the inside of the engine block will get too hot. This will show on the coolant temperature gauge.

In case your vehicle gets too hot, stop and examine the oil levels. You may require more oil. Bringing a spare oil always is a smart decision.

Equally, oil becomes dirty over time as it picks up carbon and other particulates from the engine. Eventually, it’ll turn into sludge, inhibiting the flow of the lubricant.

You can avoid this by having a regular oil and filter change – at least once per year or 10,000 miles. High mileage and fully synthetic oil help keep sludge at bay, too.

Head Gasket Problems

car head gasket

When you notice overheating, it might be coupled with a blown head gasket and a cracked engine block.

If your head gasket blows, you’ll probably notice terrible performance, a Check Engine light, Limp mode, and oil and coolant mixing. That is, you’ll either see oil in the coolant or a milky-like substance in the oil. This is also a symptom of a cracked engine block (discussed below).

Oil and coolant mix because the gasket is no longer confining the liquid flow to their respective channels. They’re free to splash around and end up in the wrong places as they pass between the block and the head.

A blown head gasket is likely a by-product of overheating, much like a crack in the block. The two can happen independently of each other (and usually do).

Nevertheless, if a mechanic finds that you have a blown head gasket, it’s worth checking you don’t have a cracked block either.

Oil And Coolant Mixing

coolant in oil

If an engine block cracks in one of the channels for the oil or coolant, the two might start to mix at that point.

It will get progressively worse, although you might overlook any performance impact at first. This is the main difference between the symptoms of a cracked engine block and a blown head gasket.

Oil Or Coolant Leaks Under The Car

transmission fluid leak

You might notice a puddle – small or large – under the car. If it’s oil or coolant, that’s never a good sign.

The oil filter or drain plug is the most likely location for an oil leak. However, it could come from anywhere with oil flow. This could include a channel within the cylinder block.

Coolant leaks, likewise, could come from anywhere. This could potentially include the channels in the engine block. However, it’s more likely to come from a more familiar location, like the radiator or a cracked rubber hose.

Smoke From Under The Hood

smoke blankets man as he opens car hood

If oil leaks from a crack higher up in the engine block, it could drip onto a hot component. This would produce an oily, blue smoke.

If you notice smoke coming up from under your hood, don’t open it! Switch the engine off and wait, obtaining your hands on an extinguisher if possible.

When the smoke eventually fades away (which it hopefully will as the car cools without starting a fire), check out the source of the problem. You might establish that it’s oil from a cracked engine block.

Poor Performance

Poor Performance

The engine won’t perform well with overheating and low oil and coolant levels. It might even go into Limp mode if the problem becomes severe enough.

For reference, a crack in the cylinder wall (within the engine block) would also certainly cause poor performance, Limp mode, and a Check Engine light (among other symptoms).

This problem can be confirmed (or eliminated) with a compression test.

This article will continue to focus on fissures in the engine block away from the cylinders. However, it’s crucial to know that a fractured cylinder wall can’t really be fixed. You’ll need an entirely new motor or car. Sorry.

What Should I Do If I Have A Cracked Engine Block?

Man calling mechanic after car breakdown

If you notice symptoms of a cracked engine block, you should pull over in a safe place and call for breakdown assistance.

Should you notice overheating while driving, you should continue as slowly as possible (concentrating on keeping the engine speed low and not applying any significant loads, such as accelerating or hills). If the temperature continues to rise into the red zone, pull over and follow the steps above.

Maybe you’re at home and found a cracked engine block? Unfortunately, your car will probably need to be towed to a shop so a mechanic can work on it thoroughly and safely.

Will A Cracked Engine Block Impact Performance?

car wheels

A cracked engine block will impact performance since it’ll lead to overheating. If the metal components of an engine get too hot, they’ll expand, putting considerably more friction on the motor.

If this gets bad enough, the engine could seize entirely – an irreparable issue.

Cracks in the cylinder walls will impact performance due to low compression. When the air/fuel mixture enters the cylinder, some of it escapes through the gap. Likewise, the force of the spark plug igniting it won’t be so strong.

These are often caused by too much pressure within the cylinder, stemming from issues with the injectors, valves, or retro-fitting forced induction.

In short, if you notice signs of a cracked engine block, take your vehicle straight to a mechanic! Getting it fixed now will save you thousands in the very near future.

How Much Does A Cracked Engine Block Cost To Repair?

Euro banknotes in female hands on car engine background

Each cracked engine block must be addressed on an individual basis. A mechanic probably won’t be able to give you an accurate quote until they’ve inspected the damage themselves.

This is because each crack is different. Its location, size, and level of damage will vary from block to block.

In most cases, a mechanic will be able to weld across the crack and smooth it down. Sometimes, they might prefer cold stitching (for tiny cracks in lower-pressure areas) or block sealants/epoxies (for extremely minor cracks).

An entirely new engine block might be needed in the most severe cases – multiple, deep, high-risk cracks in difficult-to-fix places.

You’ll pay a mechanic around the $1,500 to $2,500 mark to repair a cracked engine block, although costs could rise further. These figures are made up approximately as follows (exact costs have been left out since they vary drastically based on region and individual shop):

  • Labor hours ($65 to $125 per hour):
    • Engine removal and disassembly – 3-5 hours
    • Investigation and diagnosis – as long as it takes
    • Welding – 1-2 hours (depending on severity)
    • Testing – depends on the test
    • Reassembly and replacement – 3-5 hours
  • Materials:
    • Welding materials – $50 to $100

Can I Drive With A Cracked Engine Block?

man in car driving through street

If you have a serious crack in the engine block’s oil or coolant channels, it might still turn over and run… but you shouldn’t drive it. Every moment the engine’s on, you risk doing further damage to your car.

A minor crack – barely leaking at all – will be fine to drive with, although the only place you should be going is straight to a mechanic.

If in doubt, it’s best to be safe and err on the side of caution. Either get in touch with a call-out mechanic or have your car towed.

A cracked cylinder wall within the engine block may impact your performance so severely that the car struggles to start. You should never drive if this is the case. It’s dangerous.

Attempt to adopt a precautionary method instead. Engine and filter modifications, together with maintaining adequate coolant levels, are two vital measures to guarantee the longevity of your motor.

Damaged engine blocks are no fun. Hopefully, you never have to find out the costly way!

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Benjamin Kitchen

Ben is an IMI-qualified light vehicle technician from England with experience in a fast-fit garage. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa. It may have a tiny engine, but in eight years it's never once let him down!