Alpha I water pump problem

[Darol Wester]

This is a Mercruiser 260 outdrive lower unit. We had a nasty over heating problem of the port side exhaust hot enough to melt the 3" hose just before the elbow. We removed the lower unit and found that the white tube out the top of the water pump was melted down. The impeller is in good shape. I'm assuming that the pump tubing went first. Any ideas?

Also, this is a 1978 boat and motor. We've replaced the lower end with the Alpha I. On the older unit it shows an O ring at the top of the drive shaft in a grove just below the splines. On the newer unit there is no grove for a ring. There is a place up in the housing that would hold an O ring but we can't find the part listed anywhere. What should be at the top end of the drive shaft?

Would this missing O ring have caused exhaust to blow by and melt the tube?

Thanks

 

[Haut Medoc]

Re: Alpha I water pump problem

No, that did not cause you to overheat.......
You do not need the oring....
If you overheated on one side, I would pull the riser & check the water dumps....
I'll bet they are clogged with scale....
You are probably due for new riser/manifolds......​

 

[Darol Wester]

Re: Alpha I water pump problem

The manifolds have about 500 hrs on them. They are ran with a heat exchanger/contained cooling system. Could they go bad in that time?

Also, any idea what caused the plastic tube on top of the pump to melt or was it connected to the hot manifold? At the time of the melt down, we checked the motor temp and it was high but not over heated. It melted where it connects to the metal tube above.

 

[Haut Medoc]

Re: Alpha I water pump problem

It is the riser that is clogged, not the manifold....
500 hours should be OK for manifolds on a closed system....
But the risers are still the exhaust outlet for the raw water that cools the exchanger....
If your risers have 500 hours on them esp. in salt water use, then they may be ready for replacement.....
A riser gasket costs $5, & you will have to pull it anyway to replace the bellow.......
The only way for an over heat on one side is clogged water dumps....
That would explain your cooked exhaust bellow & the melted plastic guide.......
Exhaust exits through there....
One clooged side will not neccessarily make you over heat, but I'll bet the temp was above normal, because the raw water outlet was resticted by half..
Check your riser for clogging from scale.......
I see new ones in the near future....​

 

[Reel Poor]

Re: Alpha I water pump problem

I agree with Haut. The white plastic tube melted due to lack of water exiting with the exhaust thru the drive. No water in the exhaust flow melts rubber componants up stream (your exhaust hoses and flappers) and plastic parts down stream in the drive (water pump tube, water pump housing).

 

[Darol Wester]

Re: Alpha I water pump problem

Makes good sense. Thanks so much you guys. Always appreciated. Darol