Mercruiser 3 0 overheating

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Search Advanced search…. New posts. Search forums. Log in. For a better experience, please enable JavaScript in your browser before proceeding. Thread starter pfd Start date Jul 18, Joined Jun 24, Messages Temp used to be around I read some post and thought that my impeller was gone.

Plus rubber pieces in the intake on the outdrive good indicator. I dropped the lower unit. It's a alpha one. I replaced the impeller and it needed it. The old one was done. Put everything back together. This is fresh water cooled. Before the impeller install, I check the t-stat hoses and water pump on the engine and all seemed fine.

I forgot to say this is on the muffs on garden hose. The problem is that I'm not getting water to the exhaust manifold or to the water pump on the engine. So I turn the hose on with engine off and pull the intake hose off to the T-stat.Read More.

A new clean system under moderate load should operate at the lower end of this range and a dirty system under full load might operate in the upper range. Any temperature that reads outside of this range is abnormal and should be investigated.

Before trying to diagnose a temperature problem, check the temperature gauge. Temperature gauges, especially electric, are often inaccurate and have temperature scales that are difficult to interpret. Before investigating a suspected temperature problem, check your temperature gauge against a thermometer of known accuracy. Over-cooling Though the most common problem is overheating, the opposite may also happen and will create long-term problems.

Any good Fresh Water Cooling System should have excess cooling capacity. This compensates for the inevitable decrease in cooling capacity that results from the normal buildup of dirt on the heat transfer surfaces.

In order to make sure that such a system, when new and clean, does not over-cool, a thermostat is used to control the flow of coolant to the heat exchanger. Over-cooling can only result from the thermostat not functioning properly.

Thermostat NOT functioning properly. Check to make sure that the thermostat is of the right type. Do not assume that just because it fits it will function properly.

How To Remove Mercruiser Engine from boat

There is a lot more to thermostat design than most people realize. If the right type and correctly installed, make sure thermostat functions properly by immersing it in hot water of known temperature. The easiest way is to use a pot of water on a stove with an accurate thermometer. Hold thermostat by the flange with a pair of pliers.

Do not let either thermostat or thermometer rest against bottom of pan. It should close again when immersed in colder water. Malfunctioning thermostats cannot be repaired, they must be replaced: make sure you get the right type. Overheating Overheating problems can be categorized into three basic problems, which either alone or in combination with one another will create overheating.

They are lack of raw-water flow, lack of freshwater flow, and heat exchanger defects. Lack of raw-water flow Lack of raw-water flow will show up as an excessive increase of the raw-water temperature as the raw-water passes through the cooling system. This will create surface temperatures on the elbow that will be warm but not excessively hot. Therefore, the easiest way to identify a raw-water problem is to check whether the engine overheating is combined with excessive temperatures on the outlet side of the raw-water system.

If the raw-water side is to blame, there could be three basic reasons.Overheating problems in an inboard-outboard motor, also called a "stern-drive," happen as a result of component failure somewhere in the cooling system. One part might be responsible, or a number of parts can contribute to the overheating problem.

Even mild overheating can cause serious damage to expensive engine components. Upon any sign of overheating, a boat owner should investigate the root cause of any abnormally high temperatures.

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Installing a spark plug that has the incorrect thread length into a marine engine head can cause a run-away pre-igntion problem. Spark plug threads that extend into the combustion chamber can accumulate heavy carbon deposits, which continue to burn past the combustion cycle.

As a result, the plug electrode overheats and causes higher than normal combustion temperature. The inboard-outboard cylinder head can accumulate large carbon deposits in the combustion chamber head, valve surfaces, around the exhaust valve stem and in the exhaust ports. The heavy accumulations form a thick barrier that resists normal heat dispensation, reducing the combustion chamber volume and absorbing and holding heat after ignition.

De-carbonizing sprays use strong solvents, which when injected into the fuel intake system break up and dislodge the carbon. Overheating of the inboard-outboard motor at the raw water intake ports on the lower unit can block off the cooling water to the engine. When the small intake ports on the lower unit become clogged with twigs, mud, seaweed or plastic, they can starve the engine for cooling water. Boat owners should inspect the intake ports and free the ports, or intake screens, of all debris.

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The trim setting motor angle should not be tilted up excessively high where the ports break the water's surface and suck air. Some inboard-outboard marine engines contain a closed loop cooling system that consists of a radiator, which uses anti-freeze coolant for the purpose of cooling the engine passages and wet exhaust manifold.

Overheating problems manifest when the radiator cores become clogged with rust and residual oil and sludge. A defective thermostat stuck in the closed position will completely block the cooling fluid from circulating in the engine, leading to rapid overheating.

Rubber water pump impellers are used on all inboard-outboard marine engines. The impellers have fan-like blades that rotate rapidly to draw intake water through a raw water inlet and pump it through the various engines passages and exhaust wet manifold jackets.

If the rubber blades turn brittle with age they no longer hold their seal within the water pump housing, causing a reduced flow of cooling water. Broken impeller blades can also reduce the flow and plug a water jacket on the discharge side of the water pump. Low and-or contaminated lower gear case oil will cause an overheating problem. If the gear case oil level measures below specifications, it can cause inadequate lubrication to the transmission drive gears, which will raise the temperature of the lower unit and transmit the heat through the engine case.

Water that has contaminated the gear case oil because of ruptured seals or gaskets will breakdown the viscosity of the oil, keeping it from lubricating the parts. Improper lubrication produces friction, which produces excess heat. Outside ambient air temperatures that exceed triple digits will cause an elevation of overall engine heating, especially under dry humidity conditions.

Combined with running the engine at full throttle for prolonged periods, the engine suffers more load on all the major engine components, like the crankshaft bearings, cam, valve guides, pistons, rings and rod bearings. Constant full-throttle operation on very hot days, should be avoided, especially if towing skiers or carrying heavy passenger loads. A blown head gasket in an inboard-outboard engine will cause water to enter the combustion chamber and be discharged out of the exhaust.

The loss of cooling water that would normally circulate throughout the engine becomes reduced, overheating the affected cylinders. Blown head gaskets require major engine repair and expense. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.

To submit your questions or ideas, or to simply learn more about It Still Works, contact us. Intake Restriction Overheating of the inboard-outboard motor at the raw water intake ports on the lower unit can block off the cooling water to the engine.

Radiator and Thermostats Some inboard-outboard marine engines contain a closed loop cooling system that consists of a radiator, which uses anti-freeze coolant for the purpose of cooling the engine passages and wet exhaust manifold. Water Pump Impellers Rubber water pump impellers are used on all inboard-outboard marine engines.

Gearcase Oil Low and-or contaminated lower gear case oil will cause an overheating problem. Ambient Air Temperature and Full Throttle Outside ambient air temperatures that exceed triple digits will cause an elevation of overall engine heating, especially under dry humidity conditions. Head Gaskets A blown head gasket in an inboard-outboard engine will cause water to enter the combustion chamber and be discharged out of the exhaust.The Mercruiser stern drive is one of the most popular marine propulsion systems on the water.

It is reliable and usually the annual maintenance performed during winter layup will prevent overheating problems. But when things do go wrong with the cooling system, the Mercruiser is easy to troubleshoot and repair. This article assumes that your boat has a raw water cooling system. That is, one that draws water from the lake, circulates it through the motor, and then discharges it back into the lake. Depending on the age of the boat and the maintenance history, the most likely cause of an overheat condition is the impeller located in the lower unit of the drive.

Newer boats have a warning siren that alerts the pilot that water is not being pumped up from the lower unit. Older boats may not be equipped with the warning siren.

To troubleshoot, install a section of clear water hose at the input to the thermostat housing. If the boat is on a trailer, attach a garden hose and ear muffs to the raw water intake on the lower unit.

Start the engine. If the impeller is not working, no water movement will be seen through the clear hose. Replace the impeller and re-check for water movement through the clear hose.

What Happens When a 4.3 Mercruiser Is Overheated?

If the overheat condition only exists when the boat is run at high speeds, the cause may be clogged exhaust manifolds or risers. The Mercruiser has inspection ports on the font of the exhaust manifolds.

Remove the ports and visually inspect them for deposits that would restrict the water flow. Remove the manifolds if they appear clogged. Use a metal rod to knock rust and deposits loose from the interior of the manifolds and flush with water. Perform the same maintenance on the risers. A stuck thermostat can also cause an overheat condition.Discussion in ' Powerboats ' started by bjohanssonAug 29, Log in or Sign up.

Boat Design Net. Mercruiser 3.

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I have just bought a Maxum Bowrider 93 with a Mercruiser 3. During the last trip the engine temperature suddenly rises very rapidly.

As I slowed down the temperature remained high, and then suddenly dropped back to normal.

MerCruiser Closed Fresh Water Cooling Systems

I continued driving and after about 10 min at normal temperature it suddenly rised again. I slowed down and felt that the in-water hose was very warm and at low pressure. I turned off the engine to let i cool down. Then it ran ok the last 20 min home. It felt like the cooling stopped working completely, and then started working again.

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Could it have been problems with the thermostat? Since it's so "random" it does not sound like the impeller. I know that the previous owner recently changed the water pump. Any ideas what could cause this random overheating? Replace the thermostat. All of these engines develop temperature issues: small waterborne life deposits calcium on the copper thermostat. In some cases it doesn't close anymore, in others it refuses to open until the cooling water reaches boiling temp.

Do not postpone it, the over-temperature rapidly damages the exhaust manifold. CDKAug 30, Those engines had a series of updates on the thermostat housing and water bypass hose if installed Sometimes, they have a mis-matched set of castings or the original faulty ones and do that.

mercruiser 3 0 overheating

I had this problem with a Volvo. A fitting was corroded through letting air into the water intake hose when on a plane. Off plane, the hole was under water and the cooling system worked fine. MCDennySep 11, You must log in or sign up to reply here. Show Ignored Content.

3.0 Mercruiser overheating

Similar Threads. Replies: 5 Views: 1, Kyle Thomas Lankford Jun 7, Replies: 1 Views: 2, Ike May 17, Replies: 7 Views: 2, Replies: 10 Views: 4, AutomechMar 31,in forum: Powerboats. Replies: 5 Views: 16, Angelberto Jun 4, Replies: 4 Views: 3,Discussion in ' Powerboats ' started by mtn mikeJun 19, Log in or Sign up. Boat Design Net. Need some troubleshooting help. I am a fairly mechanical guy. I have a Sea Ray with a hp mercruiser, Alpha One outdrive.

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Haven't had the boat on the lake in several years but have winterized and tried to take care of it through the years. Upon deciding to sell it I took a friend to the lake to show him the boat. The boat ran fine for about an hour then began to loose power and spit and sputter.

I noticed the temp guage going south and shut the engine down at around deg. Had to catch a tow back to the landing. Great day for selling a boat. Anyway, I have opened up the hoses at the water pump to find the insides dry.

After I got it home I tried to flush water up through the outdrive with water muffs that slide over the foot.

mercruiser 3 0 overheating

I could not get water up to the engine. I also took the water pump off and although old it doesn't appear to be seriously faulty. After looking at some technical drawings on the net I am wondering if my problem is in the water pump in the outdrive. Does anybody have info for me? You must log in or sign up to reply here. Show Ignored Content. Similar Threads. Replies: 5 Views: 1, Kyle Thomas Lankford Jun 7, Mercruiser 3.

Replies: 1 Views: 2, Ike May 17, Replies: 3 Views: 6,Mercruiser Sterndrive Information. Mercruiser Parts. Mercruiser Help. Mercruiser Manuals. Mercruiser Tools.

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Mercruiser Sterndrives. Engine Overheat Troubleshooting Excessive overheating can ruin your engine. If your engine is overheating turn it off and do not run it until you have fixed the problem.

Your engine can overheat for a variety of reasons. It can be a temporary problem such as weed or debris wrapped around your lower unit. It can also be from a more serious reason such as a bad water pump or clogged exhaust castings.

Troubleshooting for Fresh Water Marine Cooling System

Overheating is a problem which can be diagnosed through a process of elimination. The best way to tackle such a problem is to first consider the obvious.

mercruiser 3 0 overheating

For example, if you have just run aground on a sand bar and now you are overheating, chances are good you have sucked up some sand and possibly ruined your water pump impellar. Not only will you have to rebuild your water pump but you might have to backflush the cooling system to remove the sand.

Another common typical example that we see all the time is the customer who has just started using his boat after it has been sitting for a year or more. We usually find that the rubber water pump impellar blades have turned brittle from sitting. After the impellar was used for a couple of hours it crumbled to bits and the engine overheated. If your boat has been sitting for a year without being run, you should rebuild the water pump.

One more common occurrence worth mentioning happens when a customer runs the engine out of the water without an adequate water supply. All it takes is 45 seconds of running dry and the impellar is ruined.


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