How to fix a boat engine that smokes white?
A boat engine is composed of an exhaust outlet to reject the gases created during combustion. During normal use of the marine engine, the exhaust gases should be colorless and painless. But your boat engine may be emitting white smoke. So how to repair a boat engine that smokes white? This guide explains how to distinguish between disturbing white smoke and normal white smoke from a marine engine. Next, we will explain to you what are the causes of a white smoking outboard motor. Finally, we will detail the solutions to implement to make your boat engine stop smoking.
NB: all types of marine engine can smoke white: outboard engines, 2-stroke and 4-stroke boat engines, inboard engines and even some diesel boat engines. All the solutions below can be applied to these boat engines.
Why is it normal to have a boat engine that smokes white?
In some cases, white smoke is not a sign of malfunctioning marine engine. Before panicking, it is necessary to know how to identify these precise cases where the white smoke is not a danger for the engine of the boat. Here is a list of situations where it is normal to have white smoke coming out of a boat engine:
- I have a very old boat engine that smokes white
You should know that 2-stroke boat engines that were built before 1990 smoke white. This is one of the characteristics of old marine engines. So you don't have to worry.
- I have white smoke coming out of my outboard motor on start up
At start-up, the marine engine is cold and it is normal to see white smoke appear. Indeed, at low pressure when the engine is idling, water vapor is formed. The white smoke that comes out of the outboard motor is produced by this water vapor. However, this phenomenon should not last more than a few minutes. Then, once the outboard motor is warm, the exhaust gases should become colorless and odorless. Otherwise you have a problem!
- I just bought a two-stroke fuel-injected boat engine and it smokes white.
You were happy to go out to sea with your brand new injection two-stroke boat engine! And at the first start, the boat engine emits white smoke... Don't worry, it's not a manufacturing problem whatever the brand of your boat engine (Yamaha, Mercury, Suzuki, Johnson, Honda, etc). It's even quite the opposite. Brands have designed boat engines that smoke to protect them! Indeed, during the first hours of use, the electronic control system will automatically inject more grease than necessary into the boat's engine. This excess fat will help protect the marine engine cylinders. And as you can imagine, the consequence of this overgreasing is the emission of white smoke... So during a few outings at sea, don't worry if your boat engine smokes white.
- I changed my boat engine recently and it smokes white.
The new generation boat engines have been designed with a very efficient post-cooling system in order to obtain optimum performance. These piston cooling nozzles have many advantages such as significant fuel economy, much longer engine life (thanks to more efficient temperature control), and much lower NOx emissions ( therefore a much less polluting boat engine). Carrying despite all these advantages, this new technology has a disadvantage: it causes white smoke while waiting for the temperature in the engine to increase. So don't panic even if the dashboard alarm goes off. Everything is normal. Hoping that this defect will be erased on the new generation of boat motors.
Why do I have an outboard motor that smokes white?
You should know that the causes of a white smoking outboard motor are the same regardless of its power: 6hp, 15hp, 25hp, 30hp, 50hp, 60hp, 75hp, 100hp, 150hp, 250hp, etc.
In most cases, a boat engine that smokes white is not a big concern. The most problematic exhaust fumes are blue smoke and black smoke.
There are two scenarios in which an outboard motor smokes white:
- Due to water vapor
- Due to overcooling
I have a boat engine that smokes white from water vapor
In 90% of cases, white smoke is a sign that the outboard motor is venting water vapor. There is nothing to be alarmed about but you have to solve the problem. The reasons for a white smoking boat engine due to water vapor are multiple:
- Water may have entered your tank. When the boat's engine burns your fuel, it converts this excess moisture into white smoke.
- Your engine's water circuit is scaled up. To cool, all boat engines use a water-fed cooling circuit. The scaling of this circuit produces overheating. By heating, the marine engine converts the water in this circuit into white smoke. In most cases, the problem comes from an obstruction of the water inlet by algae or plastic waste.
- Finally, the problem may come from a leak in the cooling circuit. If a seal is no longer tight then water will seep into the cylinder of the marine engine. When burning, this water will create white smoke. Even if the leak can come from any duct, there is a good chance that the problem lies with the cylinder head gasket.
I have an outboard motor that smokes white from overcooling
If your problem is not due to water vapour, then your boat engine smokes white due to overcooling. Indeed, it may be that the temperature is too low in the cylinder head and the combustion chamber. Consequently, the combustion of the fuel is not complete and there remain droplets of petrol or diesel suspended in the exhaust gases. When these fuel droplets are expelled into the air, they recondense. The diffraction of light transforms drops of more than one micron into white smoke.
So in what cases does a boat engine only partially burn its fuel? The root cause is poor/unsuitable fuel for the boat engine. If white smoke comes out of your boat engine suddenly after filling your tank, then you know that your gasoline or diesel is of poor quality. As the fuel lacks cetane, it does not burn properly and atomizes into droplets instead of disappearing as a gas.
For the more adventurous who continue to use their boat during the winter, the low temperature of the air entering the engine can be the cause of over-cooling generating white smoke.
Finally, a common cause of white smoke from a boat engine is the wear of the preheating systems. In this case, the 2-stroke or 4-stroke boat engine will have trouble starting – or worse, it won't start. The culprits are called glow plugs and air intake heater.
Finally, although more rare, it should be noted that white smoke can also appear at the outlet of an outboard motor if the coolant is too cold, if there is a problem with the blowing of the piston rings which causes the compression ratio to be too low, or if the fuel injection system is incorrectly adjusted.
Solutions to repair a boat engine that smokes white
What to do if a boat engine smokes white from water vapor
If your boat engine smokes white because of the water vapour, you need:
- Check that your gas tank is not leaking. If so, move the tank and replace the fuel.
- Check that the water inlet is not clogged. If so, remove the cap.
- Check if there is a leak in the cooling circuit. Test the cylinder head gasket first. If it is no longer tight, replace it. (You will find many spare parts on Amazon)
What to do if an outboard motor smokes white from overcooling
If your outboard motor smokes white from overcooling, you need:
- Change fuel if the problem started after filling your tank. To avoid throwing away all the fuel you have purchased, you can also add an octane booster to your tank. This should not solve the problem 100% but it will allow you to use poor quality fuel without damaging your boat engine.
- Check the condition of the glow plugs and air intake heater. If they are damaged or no longer work properly, they will need to be replaced.
- If the lack of temperature comes from an external element such as the air temperature, then you can heat the engine artificially. There are oil pad heaters and block heaters that are really economical and allow you to raise the temperature on start-up. This may help remove the white smoke coming out of your boat engine.
Conclusion on White Smoking Outboard Motors
If despite your best efforts none of the above solutions work, stop the marine engine immediately and contact a mechanic. He will be able to carry out a more complete examination of the situation and resolve your white smoke problem.
Finally, know that you just have to change the model to forget white smoking boat engine problems. Indeed, the new diesel boat engines with electronic injection are designed to no longer have this kind of inconvenience. These new generation boat engines have an innovative fuel injection system. It achieves the optimum ratio between fuel and air – increasing engine efficiency. Most importantly, allowing a cold boat engine, with cold oil, exposed to cold air to run without white smoke.
Learn more about boat motors:
How do you fix a smoking 2-stroke boat engine?
