Water flow in stern drive of an OMC 1987 4.3L GM V6 (432APARY)

[becoleman3]

The cooling system on this boat is a raw water system and the boat has been run on an inland lake that has zebra mussels.

Towards the end of last season my engine was overheating. Since the intake screens were essentially gone I thought I had some obstructions and that this was probably the issue. When I was winterizing it was not overheating when the water flushers were used over the intake so I assumed whatever was obstructing had cleared.

This spring I decided to take the stern drive off, split the upper and lower units and install new screens. After reinstalling the stern drive I ran the unit again with the water flushers over the intake and again no overheating. I now realized that the water pressure from the hose pushed it into the engine.

I put the boat in the water and it began overheating. So I checked the impeller and some of the fins were torn off and so I replaced the entire pump and after running it began overheating again.

I pulled the intake hose off at the engine's thermostat and tried the water flow test and there was no water at all coming up. I then disconnected the hose at water tube of the transom mount and the tube was clear down to there. I then took the water pump off and back flowed from the thermostat and water came out freely and some fins from the impeller came out also.

I then attached the water flushers over the intake of the lower unit and the the water did not flow that fast out of where the water comes into the water pump. I also tried flushing water back down into the lower unit from the whole from the water pump and again it didn't seam to come out of the intake screens that significantly.

Since I replaced the screens in the lower unit and installed new seals for the water supply tube I have to think that there is a clog going from the water tube entering the upper unit to the pump.

Any thoughts or suggestions of what I should try to do before I start disassembling it again?

I thought about taking the pump off again and trying to stick a wire back towards the lower unit to see if I could find any obstructions.

In the past when I've had these clogs they had cleared themselves; does anyone have any ideas on how to do this?

 

[Scott Danforth]

Your old pump vanes went somewhere and clogged stuff up. Also, your power steering cooler may be plugged

 

[Speak]

Might want make sure your impeller shaft is turning when the engine turns - cobra right ? Check that the shaft is ok

 

[becoleman3]

Thanks for both of your input!

The shaft of the impeller is turning, that is what I thought also, that's the very end of the drive shaft and was turning when I took off the water pump housing.

The power steering cooler is between the thermostat and bellows housing and the water flows both directions really well.

When I took the water pump off I tried sending a drain cleaning wire downward and it was stopping near where the lower and upper unit join and may be getting to the water passage housing. There was some resistance and so that area may be clogged or when I was assembling the water seal ring may have been nudged and blocking the passage also.

Coming back out of the water tomorrow.

 

[becoleman3]

Took the boat back out of the water and removed the stern drive and separated the lower and upper units. Anticipating that I would find a clog in the upper unit to the water pump impeller but it was all clear. I did find that the seal that goes into the upper unit at the end of the water tube was missing. I purchased two new ones for this and know that I attempted to put them in.

The last time I reassembled the units I lowered the upper over the lower and had the seal installed in the upper. Now thinking that the seal may have fallen out and fell down in the housing where the water flow around the propeller shaft. Where it went after that is anyone's guess, but could have fallen out during reinstallation to the boat through the opening to the propeller.

1) Would this missing seal prevent water from being sucked up into the water pump?

2) Should these rubber seals be put in with a gasket seal or anything to the housing or water tube.

3) What is the best way to reassemble the units of the stern drive?

a) lower the upper unit over the lower unit or
b) lower the lower unit over the upper unit​

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[becoleman3]

I had replaced the water seals when I originally did this and one of them fell out when putting it back together and must have fallen through to the housing of the propeller. The replacement ones don't fit as tightly. Put one of the original ones back in and and reassembled and pumping water again instead of sucking air.