the water pump from the factory has an extra hole coming out the side its the smaller one on the end of this pic.
i've always gone by the 30 second rule. even a NEW or emptied for winter motor that must completely fill, 30 seconds should be long enough. if it hasnt begun pumping by that point, i turn it off and give it some time to cool while i double check everything. then i might give it a full 45 seconds. but it wont overheat in less then a couple of minutes. and if its not pumping with the hose hooked up, the impeller is probably bad already anyways. however, if you do even get it near warm, its already hotter then you think it is where the heat is produced, the cylinders, and where you have tight clearances on fast moving parts, the cylinders and pistons. and if it gets too hot, major damage is quickly done. BTW, service period on a merc impeller is always 100 hours or 3 years. or NOW, before the motor is damaged, if unsure of when it was last done. when the impeller is less then $50 (and about an hour labor, if paying for it) and a new motor is THOUSANDS, you cant replace it too often. dennis, you have NO clue. i suggest getting one before you ruin the motor in your own boat. and in the meantime, keep your bad advice to yourself.
I would be a little hesitant on using an automotive water pump on a boat. The may seem similar however there are several key differences in the way they are made. excerpt from the below URL: In regard to the cooling systems, one of the major differences is found in the water-circulating pump. This is especially noticeable when you have a raw water cooled engine. Unlike their automotive counterpart, a marine pump works in an open cooling system. This type of system is extremely corrosive to the pump. Therefore, the pump must be altered for longevity. A marine pump has a special ceramic seal, stainless steel backing plate, and a bronze impeller to resist corrosion. An automotive style pump, with its stamped steel impeller, would fail due to corrosion in a short time. I have done this before, I boat in fresh water and my boat was raw water cooled, the pump was leaking after 2 seasons, wasn't worth the savings. The extra hole may have been for an optional closed loop cooling system on the boat or like was stated a heater or bypass line in a car.
This is your recirculating pump. If it is a marine pump, it will have a brass backed seal and no heater hose outlet. (have seen them in the casting, but no hole there) The only difference is the casting, as long as it was ordered for the boat, you should be OK. For got to ask, do you have a cabin heater in the boat?
