Stupid question…

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Aug 14, 2023
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I recently changed my outdrive from a alpha one gen 2 to a stern drive engendering brand that I bought used from a guy that told me was the exact same. Everything seemed to work fine as far as shifting goes, but it ran hot as soon as I got it on the water. It seems to have water running through it fine with the muffs on. I also changed the water pump impeller when I had it apart.
Also… I forgot to put the big bell housing gasket back in so it didn’t have that when it was on the water. But it still runs hot in the driveway in neutral with the muffs on. Any idea what it could be?
View attachment IMG_1335.MOV
 
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Scott Danforth

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Did you backflush the system starting at the T-stat housing?

Overheat is lack of cooling flow
 
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Thank you for the reply. No I havent, But with the muffs on I have water coming out of the transom holes and the prop. Doesn’t that mean I have flow? There’s also a lot of water coming from the spot where you can see the shift linkage. Not sure if that is normal or not.
 

Scott Danforth

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Kind of

Is your hose bib on full? 3/4" hose?

The pump in the drive will move more water than most 1/2 or 5/8 hoses can provide. So the hose has to be on full
 

QBhoy

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I recently changed my outdrive from a alpha one gen 2 to a stern drive engendering brand that I bought used from a guy that told me was the exact same. Everything seemed to work fine as far as shifting goes, but it ran hot as soon as I got it on the water. It seems to have water running through it fine with the muffs on. I also changed the water pump impeller when I had it apart.
Also… I forgot to put the big bell housing gasket back in so it didn’t have that when it was on the water. But it still runs hot in the driveway in neutral with the muffs on. Any idea what it could be?
View attachment 395019
Given the mention about the lack of gasket. Does this mean there are no seals between the mating surfaces at all ?
If so, are we sure that the water is making it past there at all ? Maybe it’s water expelled from there you are seeing ?
 

Scott06

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Thank you for the reply. No I havent, But with the muffs on I have water coming out of the transom holes and the prop. Doesn’t that mean I have flow? There’s also a lot of water coming from the spot where you can see the shift linkage. Not sure if that is normal or not.
that makes me think the water tube coming up off the pump is not connected.

I would pull the drive replace the gasket you mentioned, back flush from the thermostat to the outdrive as the PS cooler could be clogged. Look and see if the water outlet tube is ok in the drive. might verify that all the gaskets are in palace on the water pump and the damn the pump sits on is not eroded. These can cause it to suck air.

did you use a OEM merc impeller kit? Some aftermarket ones including SEI have a bad reputation. One of the professional marine mechanics who used to frequent the marine engine forum said when ever he installed a new SEI drive for a customer he would split it and put in an OEM merc impeller.

Also if you have check balls on your thermostat that feed the elbows separately from the manifolds, if these are not working properly they let too much water bypass the engine block vs supplying cooling water to exhaust until thermostat opens. Might also be worth checking the thermostat especially if the boat sat while you were finding a drive
 
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It was the bell housing rubber o-ring that I had forgot, so I put a new one on put it back together and also put a new thermostat in it (it said 140 on the top) the water pump still looked brand new not sure the brand but she is still running hot. I shut it off at 200 deg.. what is the proper running temp. Anyway? This is a video of it running with the muffs. Is the water exiting like it should?
 

Scott06

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It was the bell housing rubber o-ring that I had forgot, so I put a new one on put it back together and also put a new thermostat in it (it said 140 on the top) the water pump still looked brand new not sure the brand but she is still running hot. I shut it off at 200 deg.. what is the proper running temp. Anyway? This is a video of it running with the muffs. Is the water exiting like it should?
No water is coming out the idle relief ports on bottom sides of gimbal housing so you are not getting water up to engine.

with a 140 thermostat should run 150-160 max.
did you check if the impeller is spinning on the metal center in it.

to back flush remove drive , remove hose at thermostat housing that comes up from out drive hook it to garden hose and flush water back out bellhousing.
looks like water is coming out exhaust of drive but not getting up to engine . Wouldn’t run it long like this as you have no water getting discharged with the exhaust so rubber parts will melt

when you get it back together keep the hose coming up from drive to thermostat housing off , hook up muffs ,you should get a chit load of water , if not something is still clogging it .
 

Scott06

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Do you think it could be the water circulation pump?
Not off of what is shown.

In video linked you see water coming out the idle relief ports on gimbal housing. In your video there is none coming out there. This tells you that no water is coming up to the thermostat housing.


Even when the thermostat is closed it should be sending water into the exhaust so that it cools it . Not seeing any coming out your idle relief ports means water isnt getting into the exhaust. You need to break up the cooling system by taking hoses off and see where there is a blockage or lack of flow.

Willing to bet based on what you have posted that you are not getting water up from outdrive to thermostat housing.

If you can get your hands on a factory service manual it will have diagrams of cooling water flow. Otherwise follow the hose back from the thermostat housing to the drive. In most models there is a PS cooler on back of flywheel cover that can get clogged. Other will have a fuel cooler (MPI). just need to trace it out pull a hose off and see where you have water and where you dont before tossing parts at it
 

Stinnett21

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Did you put the key (small metal piece that fits in the slot on the impeller that lays on the flat part of the shaft) back on when you change the impeller? It's what turns the impeller.
 
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