water pump priming

[meander]

I have developed an overheating problem this season. I did not have even the slightest issue last year. I changed the thermostat and pump impeller this winter and today was the first time cruising under power. I had it running at idle previous to today and it did heat up but I found a screw on top of the water pump above the impeller and decided it might be a bleed screw. I opened it until water came out and the temp came back down to "normal". I was wondering if this screw is indeed a bleeder screw and why am I having trouble losing prime in the pump. There does not seem to be any blockage in the intake.
Any ideas?

Thanks,
Will Hicks
1975 Tartan 30

[Don Moyer]

Meander,

The small machine screw that you removed from the top of the pump is the cam shoe retaining screw. With that screw removed, the cam shoe would have nothing to keep it from moving, however assuming that you were able to get the threads to hold when you reinstalled the screw, the cam shoe must have remained in place.

If I look at the essential elements of your report; (1) water temperature OK, (2) change thermostat and water pump impeller, (3) engine overheats, I'm sort of led to assume that one of those two items is causing the problem. You can check the thermostat in a pot of hot water on a stove, and the impeller (pump performance) can be evaluated by checking the amount of water coming out of the back of the boat.

If the overheating is in fact caused by something related to your work, it could well be that the new impeller is not performing as well as the old one. This may seem strange to you, but Oberdorfer engineers tell us that in the case of high time pumps, there is a level of wear reached when the inside of the impeller chamber is worn to the point that an old impeller (being stiffer and sometimes swelled by years of being in the water) will actually work when a new one will not.

In any case, if you can determine that your total flow of water is reduced, you might reinstall the old impeller and see if you get more water. We've also had a few cases where folks have soaked their new impellers in Marvel Mystery Oil for a few days.

As a practical matter, if it turns out that your water pump has reached this level of wear, it's usually better to replace it.

Best regards,

Don