Mercury Outboard Thermostats, Water Pump Repair, Cooling

Mercury Marine Engine Thermostats, Water Pump Repair, and Cooling Resources and Information

The cooling system is essential for the ongoing functionality of your Mercury outboard engine. The water pump is a critical aspect of this system. Fortunately, PartsVu.com stocks a complete selection of certified Mercury outboard water pump repair kits to repair and replace the water pump on your Mercury outboard. 

PartsVu stocks a wide selection of certified Mercury Outboard Water Pump Repair Kits and replacement Cooling Systerm parts to fit the exact specifications of your Mercury outboard motor. Your Mercury outboard’s cooling system prevents your engine from overheating. Don’t wait until it’s too late to replace these crucial components. Need help maintaining your water pump? Take a look out this helpful water pump maintenance guide over on our blog. 

Need help finding the right Mercury outboard parts for your marine engine? Check out our convenient Mercury Outboard Maintenance Parts Charts.

We also offer helpful resources to help you maintain your Mercury outboard motor, such as:

• Mercury Outboard Service Schedule
• Mercury Outboard Serial Number Lookup
• Mercury Outboard Engine Schematics

Mercury Outboard Thermostats, Water Pump Repair, and Cooling FAQs

How do I know if my Mercury outboard water pump is bad?

One of the sure signs that a water pump is acting up is if the motor temperature starts to climb during idle or while on plane.

Typically, the normal operating range for your Mercury outboard at idle should fall within the 120 – 140°F range, most commonly right around 125 – 132°F. On plane, your outboard’s temperature will vary widely based on the temperature of the water (colder in cold water, warmer in warmer temperatures).

If your temperatures begin to consistently rise above this range at idle, you should be concerned and not use your outboard until the problem is resolved. Also, if your overheating alarm goes off, you can be sure that some issue is driving the temperature up. 

If you’ve noticed that your outboard doesn’t throttle up as normal and bogs down, you may have a malfunctioning water pump.

Essentially, the water pump won’t consistently pump a steady stream of cooling water through the lower gearcase via the inlets on the side of the lower unit. Because of this irregularity, your engine will continually heat up and cool down, creating an intermittent bog during high RPMs as the engine compensates through reduced performance. This effect masks the issue until the water pump fails completely.

What makes this condition hard to diagnose is that at lower temperatures—during the winter months or when the water is cooler—the engine may cool off due to the environment and perform normally. Then, the bog will reappear in the warmer months, warmer water, or during extended usage. 

Your Mercury outboard features a telltale hole, which emits a small, visible stream of water that passes through the powerhead. As the name implies, the tell tale helps indicate when cooling water is flowing to prevent overheating.

In most cases, a blockage often prevents water pressure from flowing efficiently from the hole. If you notice less-than-normal water falling from the hole or no water at all, insert a thin wire into the outlet to determine if it is blocked. Normal blockages include accumulated debris and salt (scaling), but insects often burrow into this hole. That is especially likley during periods when your outboard motor is being stored for the winter.

If the tell tale hole is clear and the lack of flow continues, you might have a damaged pump housing instead. In this case, you may notice water flowing from another place on your outboard, such as a crack in the water pump housing.

How often should I change the water pump on my Mercury outboard engine?

In most cases, you won’t need to replace the water pump unless the housing is damaged. 

Instead, replacing the water pump impeller every three years or sooner should avoid most water-pump-related issues and keep your outboard running in excellent condition.

However, if you’ve noticed persistent problems keeping your engine cool, you may need to replace the water pump completely. Bear in mind that replacing the entire water pump is a significant repair for your Mercury outboard motor. 

How do I replace my Mercury outboard engine water pump impeller? 

• Step 1: Begin by removing the gearcase/lower unit from the outboard.
• Step 2: Next, remove the rubber water tube seal from the top of the water pump assembly. 
• Step 3: Remove the four bolts that hold the water pump assembly in place (Note: there may be a fifth bolt located above the propeller, depending on your outboard model). 
• Step 4: Remove the water pump housing. 
• Step 5: Remove the impeller, including the two (2) nylon washers, located above and below the impeller. 
• Step 6: Remove the woodruff key from the base of the driveshaft. 
• Step 7: Remove the upper gasket, the wear plate, and the lower gasket from the gearcase.
• Step 8: Inspect the shift shaft boot for cracks or splits. If it is worn, replace it with a new one. 
• Step 9: Install the new lower gasket, wear plate, and upper gasket with the neoprene side of the upper gasket facing upward. 
• Step 10: Install the new impeller with the nylon washers above and below it. Make sure the impeller sits over the woodruff key for a proper installation. 
• Step 11: Grease the inside of the water pump housing and the top of the wear plate with marine grease. 
• Step 12: Reinstall the water pump housing while rotating the driveshaft clockwise. This will ensure that the impeller blades are turned in the correct direction within the water pump housing. 
• Step 13: Reinstall each of the four water pump assembly bolts. 
• Step 14: Install the new rubber water tube seal onto the top of the water pump assembly. 

How much does it cost to replace a water pump impeller on my Mercury outboard?

Replacing the impeller is a relatively inexpensive and straightforward repair. Depending on your model of Mercury outboard, you can expect only to pay between $15 – $35 per impeller. However, you will want to replace other components, so it is highly recommended that you purchase a water impeller kit from PartsVu to have everything you need on hand to perform a complete job. Additionally, we carry may other boating essentials to help you to enjoy your time on the water to its fullest.

Care and maintenance of your marine engine are critical. If properly maintained, it will last for many, many years. Now that you know everything that there is to know about maintaining your Mercury outboard water pump, it’s time to get to work so you can enjoy worry-free time out on the water!

How do I select the right parts for my Mercury outboard motor?

PartsVu’s Mercury Outboard Maintenance Parts Library is the perfect reference when you need to replace common parts. That’s because these parts charts make it simple to find the right parts for your particular engine to perform regularly-scheduled maintenance. 

For Mercury outboard motors, perform maintenance after 100 hours of service or one year of operation (whichever comes first). More extensive service is recommended after 300 hours of service or three years.

After this period, maintenance is often more regular as the engine ages and parts wear out. For example, 1,000 hours generally requires an in-depth assessment by a qualified mechanic. Also, if you’re usually running your Mercury outboard in a more demanding manner, the manufacturer recommends more frequent servicing.

When selecting the correct Mercury Outboard Parts, there are some essential things every boater must keep in mind before purchasing and installing parts:

• Choosing Mercury OEM parts (original equipment manufacturer) over after-market parts often yields better long-term results for your engine as these components and products are specifically designed to meet the precise tolerances of Mercury engines.

• Check (and recheck) to ensure that you have the exact part number that matches your Mercury outboard engine. It’s important to do this because Mercury has many engine models that look very similar but contain slight differences in performance. Therefore, unmatched parts may not fit uniformly, leading to malfunctions, underperformance, and severe engine damage.

• Proper maintenance is essential when it comes to extending the life of your Mercury outboard motor and should always be mandatory to retain the value of your outboard motor. While Mercury outboards are built to last, hazards like salt water, humidity, excessive heat, electrolysis, and demanding usage eventually take their toll on your motor.

• Proper storage for your Mercury outboard is required to preserve your motor for the long term. Failure to properly winterize your Mercury outboard can cause components to degrade while the engine sits and is exposed to the elements. Therefore, properly store your outboard when it is not in use.

Are Mercury 5hp 2 stroke outboard air cooled?

No, Mercury 5hp 2 stroke outboard motors are water-cooled. They require a water pump to circulate water through the engine to keep it cool.

What's the effect of changing cooling outlet on a Mercury outboard?

Changing the cooling outlet on a Mercury outboard can affect the water flow through the engine and the cooling system's efficiency. The cooling outlet directs the water flow through the engine and out the exhaust system. Changing the cooling outlet can alter the water flow and affect the engine's performance and cooling system's ability to keep the engine at the correct temperature.

Where is the thermostat on a Mercury outboard?

The location of the thermostat on a Mercury outboard can vary depending on the model and year of the outboard. In most cases, the thermostat is located on the top of the cylinder head or on the front of the engine block. It is connected to the water intake and regulates the engine's temperature by opening and closing as needed to allow water to flow through the cooling system.

How to change the thermostat on a Mercury outboard?

The process for changing the thermostat on a Mercury outboard can vary depending on the model and year of the outboard. In general, the process involves locating the thermostat, removing the housing cover, removing the old thermostat, installing the new thermostat, and reassembling the housing cover. It is important to refer to the outboard's owner's manual or a reliable online guide for specific instructions for your particular model.

Can I run my Mercury outboard without a thermostat?

It is not recommended to run a Mercury outboard without a thermostat. The thermostat is a critical component of the outboard's cooling system, regulating the engine's temperature by opening and closing to allow water to flow through the cooling system. Without a thermostat, the engine may overheat, causing damage to the engine and potentially leaving you stranded on the water. If you suspect your thermostat is faulty, it is recommended to replace it rather than run the outboard without one.

How to replace a water pump on a Mercury outboard?

1. First, remove the lower unit of the outboard motor.
2. Remove the water pump housing cover and impeller.
3. Inspect the condition of the housing, the impeller, and the gaskets and seals.
4. If the impeller or any of the gaskets or seals are worn or damaged, replace them.
5. Lubricate the new impeller and reinstall it, along with the new gaskets and seals.
6. Reinstall the water pump housing cover and the lower unit.

(Note: This procedure is related to such questions as: How to replace water pump on a 20 hp Mercury outboard? / How to replace water pump on a 25 hp Mercury outboard? / How to replace water pump on a 60 hp Mercury outboard? / How to replace water pump on a 7.5 Mercury outboard? / How to replace water pump on a Mercury 115 outboard? / How to replace water pump on a Mercury 40 hp outboard? / How to replace water pump on a Mercury 50 hp outboard? / How to replace water pump on a 115 hp Mercury outboard?)

Where is thermostat located on a 90 hp Mercury outboard?

The thermostat on a 90 hp Mercury outboard is typically located within the thermostat housing, which is usually mounted on the cylinder head of the engine. To locate the thermostat, you will need to follow the upper radiator hose from the top of the engine block to the point where it connects to the thermostat housing. The thermostat itself is a small, spring-loaded valve that regulates the flow of coolant through the engine. It is important to consult your engine's owner's manual for specific instructions on how to locate and replace the thermostat.

What cools exhaust on Mercury outboards?

The exhaust on Mercury outboards is typically cooled by water. Water is pumped from outside the boat through the outboard's cooling system, which includes the exhaust system, to help regulate engine temperature and prevent overheating. As the water flows through the exhaust system, it absorbs heat and then exits the outboard through the exhaust.

Where can I learn more about Mercury Outboard Parts?

PartsVu understands that boaters want to learn how to perform their own Mercury outboard maintenance. From maintaining your Mercury outboard, Mercury sterndrive, and MerCruiser engines, there’s always something new to learn and save money. That’s why PartsVu offers our comprehensive blog, The Partsvu Xchange. 

Read up on the latest developments in boating, as well as search for everything you need to know about Mercury outboard motor maintenance.

To get you off to a good start, these are some of the most important articles on Mercury Outboard Thermostats, Water Pump Repair, Cooling System issues, and more:

• Maintaining Your Mercury Outboard Water Pump
• Mercruiser Serial Number FAQs
• How to Select the Right Mercury Outboard Parts
• Mercury Marine Maintenance Archives

What is the most common Mercury outboard thermostat problem?

The most common Mercury outboard thermostat problem is the thermostat failing to open or close properly, which can cause the engine to overheat or run too cool.

What can happen to my engine if I experience Mercury outboard thermostat failure?

If you experience Mercury outboard thermostat failure, your engine can overheat, which can lead to serious damage to the engine. Overheating can cause warping or cracking of cylinder heads, the block, or other components, which can be expensive to repair or even require a complete engine replacement. Additionally, overheating can cause damage to the pistons, bearings, and other moving parts, which can cause decreased engine performance and longevity. Therefore, it is important to replace a faulty thermostat as soon as possible to prevent potential damage to your engine.

How do I start troubleshooting Mercury outboard cooling system blockage?

To start troubleshooting a Mercury outboard cooling system blockage, you can follow these steps:

1. Check the water pump: Start by checking the water pump to see if it is functioning properly. Check the pump housing, impeller, and wear plate for any signs of damage or wear. If any of these components are damaged, they can cause a blockage in the cooling system.
2. Check the thermostat: The thermostat is responsible for regulating the flow of coolant through the engine. If it is stuck closed, it can cause the engine to overheat. Check the thermostat to make sure it is functioning properly.
3. Check the water jackets: Check the water jackets to make sure they are not clogged with debris or corrosion. Use a wire brush to clean out any debris or corrosion.
4. Check the water intake: The water intake is responsible for bringing in water to cool the engine. Check the intake to make sure it is not clogged with debris. You can also check the water pump inlet to make sure it is not blocked.
5. Check the water pressure: If the water pressure is low, it can indicate a blockage in the cooling system. Check the water pressure using a water pressure gauge.

If you are unable to identify and fix the blockage, it is recommended to seek assistance from a certified Mercury outboard mechanic.

What comes in a Mercury outboard thermostat kit?

A thermostat kit for Mercury outboards typically include a new thermostat, a gasket, and sometimes a seal. Some kits may also include additional hardware or parts, depending on the specific model and application. It is important to ensure that the kit is designed for your particular engine model and year before purchasing and installing.

Is a 60 hp 2 stroke Mercury outboard water pump replacement generally the same procedure as a 60 hp Mercury bigfoot outboard water pump replacement?

The basic procedure for replacing the water pump on a 60 hp 2 stroke Mercury outboard and a 60 hp Mercury bigfoot outboard is similar, but there may be some differences in the specific steps involved due to differences in the two outboard models. It is important to consult the manufacturer's instructions or a repair manual specific to your outboard model to ensure proper procedure.

How to clean a Mercury outboard thermostat?

Cleaning a Mercury outboard thermostat involves the following steps:

1. Remove the thermostat housing from the engine.
2. Remove the thermostat from the housing.
3. Inspect the thermostat for any visible damage or corrosion.
4. Fill a container with hot water and a mild cleaning solution.
5. Place the thermostat in the container and let it soak for 15-20 minutes.
6. Use a soft-bristled brush to gently scrub the thermostat, paying special attention to the small passages and crevices.
7. Rinse the thermostat with clean water and inspect it again for any remaining debris or corrosion.
8. If necessary, repeat the cleaning process until the thermostat is completely clean.
9. Dry the thermostat with a clean cloth and reinstall it into the thermostat housing.
10. Reinstall the thermostat housing onto the engine.

It is important to note that not all thermostats can be cleaned and some may need to be replaced if they are damaged or corroded beyond repair. It is also recommended to follow the specific cleaning instructions provided in the owner's manual for your Mercury outboard model.

What tools do I need for removing thermostats on Mercury outboard engines?

Mercury outboard thermostat removal typically requires the following tools:

1. Socket wrench
2. Socket set (various sizes)
3. Pliers
4. Screwdriver
5. Gasket scraper
6. Heat-resistant gloves
7. Heat gun or propane torch (to heat up the housing if the thermostats are stuck)
8. New thermostat gaskets (to replace the old ones)

The specific tools required may vary depending on the model and year of your Mercury outboard engine. It is important to consult your engine's manual or a professional technician for specific instructions and recommendations.