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Overheating

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76sporty

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Mercruiser 5.7 overheating. I just replaced the water pump in the lower unit (alpha 1 gen 2)I also replaced the engine water pump and thermostat. Now when I run it at idle the temp keeps rising beyond where it used to (normal temp 175)to the point the engine temp alarm comes on. Running it on muffs. Water is coming out of the exhaust. Don't know where to begin.
 
(I just replaced the water pump in the lower unit (alpha 1 gen 2)(I also replaced the engine water pump and thermostat.)

Did you twist the impeller correctly in the cup as you slide it down the shaft? Is the thermostat in correctly...it sounds like it is not opening up. I would start with the T'stat first. Feel the hoses to see which are hot and cool.
 
When I installed the impeller into the housing I rotated the shaft clockwise holding the housing down until impeller seated in to housing. How can you tell if the water lift tube is installed correctly? Once the lower and upper drive are close together you can not see anything inside the two halfs.
 
How can you tell if the water lift tube is installed correctly


Water will exit the transom, its done by feel. As your raising the lower get 2 fingers in there to feel the water tube enter the plastic guide
 
Made sure all hoses were tight, ran motor again overheated. Feeding hose to housing was very hot. Hose going to water pump was very hot. The 2 hoses going to rises were warm, not hot. Risers were the same as hoses going to them, warm .
 
CHECK the T'stat operation by removing it and suspend it in a pan of water. You need a thermometer to see what temp it opens.
Use a Merc T'stat with grounding washers.
 
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GLM = Good Luck Marine
What RU U waiting for? Did you pull it and test it?

I test the OD impeller by removing the prop and lowering the OD into a large container filled with water and a water hose running in it.
 
didnt have a chance to check temp on thermostat. starting pulling things to see if i had any other blockage. when should the risers and manifold be replaced? 201225616_10208530283411772_5831500471508337512_n.jpg198018573_10208530283171766_6846459742853243681_n.jpg199080845_10208530284771806_8937439952771453035_n.jpg
 
What are you doing?

Is this boat run in salt water and if so how often?


There are only 5 possible issues.
1. Water flow/volume decrease from (drive impeller)(pinched or collapsed incoming water hose between gimbal housing and transom) (debris in general or debris from impeller causing clog)
2. Water re circulation (Engine water pump)
3. loss of temp control (thermostat or debris in thermostat housing interfering with thermostat)
4. Water flow out (exhaust elbows clogged)
5. Bad thermostat/sender/gauge


Always start at the drive impeller and work you way down the list.

if you think it better to pull apart everything and replace a bunch of unnecessary parts feel free to do so its your money but you should follow the recommendations above
 
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the boat is ran in fresh/brackish/saltwater.(every weekend during boating season) i don't know the history on this boat from previous owners.

are these risers and manifolds usable? i also have a flapper valve missing.
 
Not knowing maintenance is all the more reason to replace outdrive impeller.

Ya elbows look a bit aged but have seen worse.
Salt/brackish water use on raw water cooled usually means every 3-5 years elbows at a minimum and possibly exhauat manifolds also.
Close inspection of thermostat housing as the same scaling seen in elbows can exist in there also.
All those parts are cast iron and do not do well with salt/brackish water.
Either does the outdrive impeller, that will be marginal also in 3-4 years.
 
I just replaced the water pump on the lower unit. also replaced the circulating water pump on engine and cleaned(housing) and replaced the thermostat. this is when i started getting the over heating issue. i don't know where the other flapper is. might be blocking exhaust. going to put a scope down the exhaust port to see if anything is blocking it. my question is do i take a chance and reinstall the elbows back on risers or replace them.
 
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