water pump not pumping when on plane! why?

[bryanwess2000]

I recently installed a waterpump repair kit on my 1977 850 merc. and it stops
pumping water and starts blowing steam out of the telltale after about 5-10 secs once the boats on plane. I then throttle back and come off plane and the telltale resumes spraying water after about 5secs. Any help would be appreciated. the boat is a 1986 glasstream 1550 pro bass. The prop shaft is
8-9 inches below pad so it should be picking up plenty of water. A couple of things that come to mind are that I ground off a tab that was sticking out on the inside of the water pump insert and that I installed a different prop on the engine. thanks for the help!

 

[emckelvy]

Re: water pump not pumping when on plane! why?

Are you talking about the 'tab' that's punched-out of the top of the insert and goes into a slot in the top of the water pump body?

That tab is supposed to positively locate the pump insert, and I suspect keep it from moving around in the pump body.

By removing this tab, you've likely allowed the insert to move around and possibly block or partially block, a critical passage.

I take it that before this, it would pump water normally?

You might want to pull that lower unit down again and inspect. I bet you're gonna need to replace the insert and also the pump body. Make sure that the flat stainless 'impeller plate' under the impeller is in good shape, too, with no scoring or excessive wear.

You can pick up an entire pump kit for a reasonable price here and elsewhere, might not be a bad idea to renew the whole works and be done with it!

HTH & let us know what you find when you open it up..........ed

 

[bryanwess2000]

Re: water pump not pumping when on plane! why?

Pulled the lower unit this week and found that the water pump base was not properly seated and caused the impeller to burn up. I installed a whole water pump kit with base and housing and got it out on the water yesterday. I ran the oil mixture at 32:1 and only ran it at mid rpms. The motor ran great but now water is dribbling out of the #1 spark plug hole. This has me thinking I
blew part of the head gasket or warped the head or possibly cracked a water jacket. The compression checks the same as it did prior to overheating.
I ran the motor off and on for about 2 hours yesterday. Any ideas about the water leaking out of the spark plug hole?

 

[jeff_smith_0423]

Re: water pump not pumping when on plane! why?

Around the spark plug hole, or FROM the spark plug hole? I had that same motor and the cylinder head is integral to the block. No gasket. There IS a water jacket there though. It's possible that has begun to give way from overheat.

 

[emckelvy]

Re: water pump not pumping when on plane! why?

Betcha the cyl block water jacket cover gasket was "cooked" when your motor got hot, now you've got real good water pressure so it leaks!

Easy gasket to replace if all the bolts come out. If they don't, a combination of heat (propane/MAPP torch etc) followed up with penetrant such as PB Blaster should persuade the reluctant bolts out.

If the water leak was from a cracked block, you'd either have poor compression readings and/or water would be showing up on the tip of the spark plug.

HTH........ed

 

[jimmbo]

Re: water pump not pumping when on plane! why?

A new gasket might not fix the problem. The water jacket cover might have warped when it got hot. Happened on my inline. Cure is to replace the cover. Install new gasket dry, no sealer on it.