Mercruiser overheat after running a ground

jdemeza

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Joined
Aug 24, 2003
Messages
6
I recently drove a friends 2000 Fountain with a large Mercruiser I/O (502?) up on a shoal and ever since then the boat is overheating. I cleaned out the inlets at the front of the bullet and now it runs at about 170 at idle. However, when it was driven today it quickly overheated. What could be causing my overheat?
 

Trent

Captain
Joined
Nov 17, 2001
Messages
3,333
Re: Mercruiser overheat after running a ground

My bet the impeller is shot. Time to drop the lower part of the outdrive to have a look see.
 

goleft24

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Aug 30, 2003
Messages
7
Re: Mercruiser overheat after running a ground

Is this motor raw water cooled or does it have a heat exchanger?IF RAW WATER COOLED, You may have sand in your block, manifolds, or riser elbows.Sand in the heat exchanger may also be a possibility If it is a closed system. After water pump inspection and or replace, Check to see if your elbows are hot.If they are blocked,they will run hot even in idle.They should be cool to the touch. If they are,you need to flush motor.If raw water, remove smaller hoses at thermstat housing leading to manifolds and flush with a hose with a good amount of pressure. Closed system, remove raw water hose that feeds exchanger and flush that.Good luck ,,I hope i helped. Mark
 

jdemeza

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Joined
Aug 24, 2003
Messages
6
Re: Mercruiser overheat after running a ground

Flushed the cooling system and it seems to be staying under temperature, however, the starboard side is running hotter (155 degrees) than the port at the riser (100 degrees) elbows. What is the best way to flush the riser or should I be looking elsewhere for the problem?
 

goleft24

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Aug 30, 2003
Messages
7
Re: Mercruiser overheat after running a ground

The cooler water is taking a path of least resistence. Could be that the starboard side is not as clean as you may think.Water is delivered to the manifolds and both risers equally. Any blockage will send more cooler water to the opposite riser resulting in the other to run hot. The only water that passes through the blocked one is water from the block.(If raw cooled)Have you determined that your impellar in the drive is OK? An impellar may look ok, but may need replacing. Sorry for this simple question but, is this the first time since this problem that you have felt the elbows? Do you have risers between elbows and manifold? If so ,Gaskets are different. Riser gaskets allow more water to flow through them than those without risers. Also check oil cooler(PORT SIDE BEHIND ALT) for any blockages.Impellar may have pieces broken off and may be blocking flow.This is a tedious task trying to pinpoint these problems.I know it can be frustrating. If you change the impellar, while the boat is out,also check the hose that runs through the gimble housing. It's slightly bigger than an inch and after time can crack! Work your way up from the drive by removing hoses from thermostat housing, and flush with a hose through the manifolds and elbows.If you feel any back pressure, you may still have a problem.I hope i helped. Mark
 

jdemeza

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Joined
Aug 24, 2003
Messages
6
Re: Mercruiser overheat after running a ground

It is raw water cooled. We removed the pump (it was a belt driven pump) and inspected the impeller. It looked to be in good shape. We flushed (with a hose) from the pump out (to the outdrive), from the pump to the thermastat, from the thermastat to the risers, and from the thermastat out the exhaust. This resulted in removing a lot of mud. We pumped water through until it ran clean. We also checked the thermastat by placing it in a boiling pot of water. This is the first time I have felt the elbows. Check http://www.mercruiserparts.biz/partsimages/CRUISER/809500.99/12.gif to see the riser and exahaust manifold. Thanks, you've been a great help so far.
 

goleft24

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Joined
Aug 30, 2003
Messages
7
Re: Mercruiser overheat after running a ground

Glad to be helpfull-Let me know how you made out. Mark
 
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