6 Symptoms to Detect a Bad Coil on Your Mercury Outboard

Mercury outboards are durable and pretty reliable. There are very few times when these boats fail to perform. Most of the time the reason is a problem with the coil.

A Mercury boat starts to show some symptoms when it has a bad coil issue including poor performance, misfire, difficulty starting, overheating, and a few more. When the outboard will start showing these symptoms, do not waste time and inspect the coil to take further steps.

In this blog, we will show you those symptoms in detail and also some ways to replace or repair the bad coil.

What Are the Signs of a Faulty Coil on the Mercury Outboard?

Mercury outboard motor is designed to give long-term service without any trouble. But a bad coil can ruin your weekend by stopping your outboard suddenly. 

Without any massive reason, a coil never stops all of a sudden. It starts showing some signs that it has bad health and it is dying slowly.

Your outboard might have some other problems as well. But the below symptoms will alarm you about the upcoming big problem:

Symptom 1: Leakage of Oil or Cracks on the Body

The coils of some mercury outboards are sealed inside a unit with oil. There is no chance of any leakages. If you find any oil on that unit’s body, it means it surely has a crack on it.

In other outboards, coils are inside a unit without oil. A crack on that unit is also a sign of a bad coil. When the coils have physical damage or get hit by something, these symptoms can come out to indicate a bad coil condition. 

Symptom 2: Difficulty to Start

A very common and most seen symptom of a bad coil is you cannot start the engine at ease. Sometimes the engine immediately goes off after starting. 

This on-and-off condition can happen repeatedly. A bad coil or dead is the common reason for this, but still, there could be some other reasons for this

When the coil is in a bad condition, it fails to produce the required amount of spark that it should have every time. The engine will find it difficult to start then. That means a hard or no start is a genuine symptom of a bad coil.

Symptom 3: Engine Misfires

The coil is supposed to produce a good voltage to run the engine smoothly. When enough voltage is not produced, the engine may run in an irregular rhythm. Your engine may make some strange sounds while accelerating.

Sometimes it shifts to a rough acceleration from smooth acceleration suddenly without any command. When you experience these things, which shows you have a bad coil for sure.

Symptom 4: No Spark at the Spark Plug Gap

When an outboard coil has a bad health and produces low voltage, it will produce a pretty less spark which we have said earlier. 

But when the coil is completely dead, it will lose the ability of producing any voltage and you cannot see any spark, not even a weak or less amount spark.

So, beside a less spark, no spark is also a sign of a dead or damaged outboard coil. 

Symptom 5: Burning Smell

When the coil of your Mercury outboard is having some problems, you usually smell it before you see it. you will start to have a burning smell when you start the engine. 

If you are having the smell frequently, it means there is an overheating or burning in your motor. Overheating of the coil can cause this issue. 

So, when you smell something burning, stop the engine and call an expert. Because it is a clear sign that your outboard has a bad coil.

Symptom 6: Low Acceleration

An outboard from Mercury can get up to 3000 RPM easily on full throttle. When you have a bad coil situation, you would face some difficulties to accelerate and the RPM can hardly reach up to that optimal level. 

You can also hear some strange sounds while accelerating more. These could possibly happen because of a bad or failing coil. You can try shifting both coils when you see this symptom.

Testing the Coil on a Mercury Outboard

When you are facing the above symptoms, now you are sure about where you should inspect. 

But only with the symptoms you cannot diagnose the exact problem of the bad coil or be 100% sure about a faulty or dead coil. To find the cause, you have to inspect and test the coil.

Test 1: Starting the Engine

You can do this test on your own. Remove the spark plugs wire before you start testing the coil of your Mercury outboard. 

Removing the battery cables and then switching on the key is also good. Now, wait for a few seconds to start the engine before turning off the key.

If the engine starts within 10 seconds, you do not have a problem with the coil. But if the engine does not start, that means you probably have a dead or bad coil.

Test 2: Checking the Resistance and Secondary Circuit

Take a voltmeter and set it to OHMS as you are about to test the Resistance. Now, take one probe from the meter and place it onto the positive terminal and another onto the negative terminal. 

If the reading is not between 0.02 to 0.04, it means the coil has some faults for sure.

Now take out the positive probe, which is probably red and place it on the tower of the coil. 

It will taste the secondary circuit. If you do not get a reading between 8 to 11, your coil is probably dead or has some faults.

3 Possible Causes of Bad Coil on Mercury Outboard

There are a few causes for which you can have a bad coil on a Mercury outboard. Some of them are very rare and can happen once in a thousand cases. So, we are not going to talk about them. 

Here are 3 of the main and common causes of a bad coil on a Mercury outboard:

  1. Corrosion
  2. Improper maintenance
  3. Lose connection

Replacement and Repair Costs of Mercury Outboard Bad Coil

It is always better to replace a lousy coil than repair it. Because in both cases the cost is almost similar. So, why repair a bad one when you can have a new coil for the same price? Here is an approximate cost to replace a lousy coil:

Item nameCoil priceLabor cost
Ignition coil35$-300$100$/hour

The labor cost is the main point where you will need to spend a good amount of money. 

Generally, it takes about an hour to complete. If there are other complications, it might take another hour. In that case, the labor cost will become 200$ for 2 hours.

Tips for Maintaining the Mercury Outboard Coil to Prevent Future Failures

As we said earlier, Mercury outboards are durable, but you need to do regular maintenance to keep them in good shape. The same thing goes for the coil. Here are some tips to help you out:

  • Check the oil level and always try to keep it at least half filled.
  • After every use, flash the boat out.
  • After every 100 hours of use, change the engine oil, lube, and oil filter.
  • Change faulty spark plugs.

Frequently Asked Questions

We understand you may still have some confusion regarding this. We will try to answer all possible doubts from your side in the below FAQ section:

Is it necessary to inspect the Mercury outboard coil often?

Yes, you should check it frequently. If you find anything unusual while riding the boat, check the coil condition when you return. Try to do this once a month at least.

From where you can change a bad coil?

You can contact any professional mechanic that you know. Or you can contact various service providers to do this for you. From some providers, you can buy a new coil as well.

After noticing the symptoms how much time you may take to change or repair the coil?

Start inspecting the coil immediately after sensing any sign of a bad motor unless you want to be stuck in the middle of the lake. When the coil is showing you symptoms, it can die anytime.

Final Words

In conclusion, keeping an eye out for these symptoms can help you catch a bad coil on your Mercury outboard early and prevent any further damage to your boat. Regular maintenance and inspection of your outboard can also go a long way in preventing issues like this from arising in the first place. Don’t hesitate to seek the help of a professional if you suspect a problem with your outboard coil.

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