How to Diagnose a Cracked Block Mercruiser- 7 Signs Don’t Neglect

Do you have a boat with Mercruiser? After a long hard winter, you should ensure whether a crack block is in your Mercruiser or not. Or, if you are purchasing a used boat engine, you should check if there is any cracked block.

It is not easy to diagnose a cracked block. Sometimes cracked blocks can give so many strange symptoms that are hard to identify. To ensure if there is any cracked block in Mercruiser, you have to know how to diagnose a cracked block Mercruiser.

In this article, we will give you some practical information about the different symptoms of a cracked block in your Mercruiser. It may help you to diagnose a cracked block.

Causes Of A Cracked Block

The Mercruiser block may crack because of pouring cold water in the hot radiator. Sudden changes in temperature cause cracks in the block. If you store your boat outside in the winter may winterize the engine and cause a crack in the block.

How To Diagnose A Cracked Block Mercruiser

If you have any doubt that your Mercruiser has a crack block and you want to ensure that you have to remove the engine, you should check it professionally. Some symptoms of cracked block Mercruiser will help to let you know if there is any cracked block.

1. Water In A Bilge

First, you should check if there is any water in the bilge. Then make sure that the water found in the bilge is there because of it raining.

If the cause of the water is not raining then verify if someone accidentally slipped the water in the boat, if this is not at all then it is for sure that there is a block cracked.

2. Excessive White Exhaust Smoke Coming From The Engine

Watch for white exhaust smoke.  If there is excessive white smoke coming from the engine, not blue or black, there must be a cracked block.

The smoke is due to emission fume leaking through the crack instead of the exhaust system.

3. Odd Sound

If the engine is making an odd sound during the start of the boat, it would be a sign of a cracked block.

4. Bad Compression

In an engine, internal combustion allows engine compression to take place. When the combustion occurs in the cracked engine block Mercruiser, the crack form in the block results in reducing pressure because of air escaping.

You can perform a cylinder leak-down test to detect a cracked block. It is one of the most useful tests to find the crack.

A cylinder leak-down test is a static test. The test measures how much pressure lost in the engine. The cylinder fills with stress, and then the tester will measure the volume of air needed to maintain the pressure in the cylinder. The reading will show in percentages. A good cylinder reading should remain below 5-8%.

5. Oil Loss Its Shiny Aspect

Take a look at the oil of the engine. If the oil looks shiny as always, then there is no problem. If it is not, the oil loses its shiny aspect. It seems dirty opaque or doesn’t seem pure; then it is for sure that there is a crack in the block.

6. Bad Performance Of The Engine

If you are the owner of the boat, then you would know better about your boat performance. You can feel about your boat’s good or bad performance, whether your boat is running smoothly or not.
If you are steering another person’s boat, it is hard to realize the cracked block on taking one ride with the boat.

7. Flying Bits Of Metal

Flying bits of metal is one the clear indicator of the cracked block.

What Should You Do?

Do not take each symptom separately. Experiencing any one of the reasons may not be responsible for cracked blocks. It can be for a different reason.

If you experience more than one of the symptoms, it may be the reason for a cracked block. It is more confirmed if you are experiencing three or more symptoms.

If you are no expert in identifying the symptoms, you can take help from an experienced person or a mechanic.

After confirming the cracked block, you should remove the engine and seal the cracked block. And take the necessary steps of how to fix a cracked marine engine block. Mercruiser cracked block repair method is very easy, so you may need to replace the motor.

Frequently Asked Questions(FAQs)

Can I weld a cracked block?

You can weld the cracked block if the block is made of steel but iron. Welding of the block may ruin the shape of the block of the engine.

What can cause block cracking?

If you do not drain the raw water from the river. It may cause winterizing the boat engine and cracked block Mercruiser.

How much will cracked boat engine block repair cost?

Cracked boat engine block repair will cost approximately $1,500 in parts and machining costs. Depending on the damage, it will take 12 to 35 hours to repair.


If your boat engine is not performing well or it takes more time to get a start or make an odd sound. You should check if there are two or more symptoms. ItMercruisermed that your Mercruiser has cracked block.

This article discussed the symptoms of a cracked block of Mercruiser. It will help you to know how to diagnose a cracked block Mercruiser, as presented.