Mercruiser Cooling problem

[jpopp]

Have '85 I/O with I-MR drive, started engine with muffs on, didn't appear that water was being pulled up through outdrive so I replaced impeller and housing, which looked pretty bad. Tried it again today and still not pulling water up. Accidentally did it with both hoses off of thermostat housing and was able to observe that no water was getting to the housing. Is that the path it takes. It gets pulled through the intake by the impeller and waits atop the thermostat until it opens. But where does the actual water pump that is attached to the front of the engine, come into play. Once the thermostat opens does it then pump water through the block or does it pull the water to the thermostat. Any suggestions as to what I should do next.

 

[Blk-n-Blu]

Re: Mercruiser Cooling problem

jpopp, Consider a regular auto engine which has water/coolant in a closed system, when the thermostat is closed the coolant bypasses back to the radiator and when it opens allows the flow through the engine.With a boat (raw water cooled) no radiator, water is picked up by outdrive impeller/pump and fed to the thermostat housing where some water is diverted to the risers/elbows to cool the exhaust and expelled through the outdrive/prop. when t-stat opens the engine water pump forces the water through the motor and manifolds and out the exhaust. So adequate water is needed from the outdrive to overcome the loss at the exhaust. Hope this helps. Usually with the muffs and hose you can overpower the impeller pump and will see very little water expelled until the thermostat opens,but watch the engine temp while on the muffs and try to run about 1100-1200 rpm. Good Luck.

 

[kcole683]

Re: Mercruiser Cooling problem

If no water is getting up from the drive to the thermostat housing it sounds like the hose/or water passages are blocked.<br />Was the impellar missing any vanes??<br />If so you need to find them.<br />Blow through the hose from t-stat to drive and see if is blocked,or the hose is shot from the outdrive through the gimbal housing.<br />If the hose checks out then back to the impellar and pump housing,make sure everything is in good condition and that the impellar key is installed.<br /><br />good luck

 

[Bondo]

Re: Mercruiser Cooling problem

When the T-stat is Closed, the water that's In the Block, is recirculated in the Block.......<br />The water coming in from the seawater pump is Dumped into the Exhaust Manifold,+ Dumped overboard.......<br />When the T-stat Opens, the seawater is circulated thru All of the system,+ Then dumped overboard......<br />If you remove only the Small Hose, coming From the outdrive to the T-stat, You Should have a Large flow of Water.... <br />T-stat Open, or Closed..........<br />If Not, That's Where the Blockage is.........<br />Blk-n-Blu, You've got it Backwards....... Water circulates in the Block, till the T-stat Opens,+ Then it runs thru the Radiator........ <br />

Was the impellar missing any vanes??<br />If so you need to find them.

spark-chaser is Right.........