sterndrive water pump loses siphon

[drewmaster]

I have a 1975 Viking deckboat I'm trying to restore. Model 990226A1 with an inline 4 cylinder 140 hp OMC selec-trim, sterndrive. I have put the whole water pump kit in with new impeller with housing. I have the sterndrive submerged in a big tub and when I start it up every time I have to hold the hose on the water inlet tube to get the pump to start sucking. Once it starts it pumps fine. I pulled the hose off the thermostat housing and filled a gallon jug in about 17 seconds. There is a new thermostat installed already. On the other side of the thermostat housing I get very poor water flow initially then it stops altogether and I had to shut her down. There is a little water dripping from the left pivot cap and a small amount sprays from the junction of the upper and lower gear box. Since I had it running I installed a new water pump on the front of the engine and the pivot cap and exhaust housing gaskets should be there today. Once they are installed and the sterndrive are back on I'm going to try it out but I have a feeling I'm still going to have it losing its water siphon after the engine is shut down. This is the last thing I need to square away before I can FINALLY put her in the water. Do you think the loss of siphon is due to the pivot cap leaking or perhaps something else I haven't thought of. And is the new engine water pump going to restore good flow to the manifold on the starboard side?

 

[Scott Danforth]

Re: sterndrive water pump loses siphon

my first guess is that your test tub isnt tall enough. I used to use a cut-down 55 gallon garbage can

 

[Boomyal]

Re: sterndrive water pump loses siphon

As to the leak at the pivot cap, maybe the big oring fell out of the groove in the end of the OD trunion? That happened to me when I last had the OD off. Fortunately I saw it rolling around on the ground before it disappeared under the boat. If I had not seen it, I probably would not have noticed that it was missing andI am sure my pivot cap would have been squirting as well.

 

[drewmaster]

Re: sterndrive water pump loses siphon

As for the tub- the intake is about 6 inches under water and has good suction once it starts. The O-ring was toast so I already replaced them with garden hose washers as they were the same size. I thought it might not be thick enough so I plan on perhaps doubling the left one when I remove it again tomorrow. Will let you know what happens. Thanks, Drewmaster

 

[Scott Danforth]

Re: sterndrive water pump loses siphon

6" is not enough. when you first put your boat in the water, the intake is at least 18" under water.

you should have water about 3-4" above the anti-cav plate at a minimum.

 

[drewmaster]

Re: sterndrive water pump loses siphon

If the anti-cav(or anti-ventilation) plate is the wide horizontal fin-like structure above the prop then it was 4-5 inches below the water. The inlet is on the underside of that plate which I estimated was ~6 inches below the surface.

And Boomyal, at first when u mentioned the O-ring in the end of the OD trunion I thought you were talking about the rubber washer under the trunion cap. I located the proper O-ring and the left one was quite flat, luckily I have one from my "donor" OD that came with the boat! Hopefully that will fix the dripping and the loss of siphon. Thanks guys, Drewmaster