Mariner 30hp not pumping water

[Sandy-man]

A friend of mine bought a 16' boat with a Mercury Mariner 30AE, approximately 1980. Second time on the water it overheated, not pumping water. He pulled the lower end unit and installed a new impeller. Still not pumping.

Is it possible the thermostat is no good or maybe water jacket plugged up with a piece of plastic or other debris that may have gotten sucked in? What's the best way to flush out the water jacket?

Any help would be greatly appreciated.

 

[wn6ngp]

How did you know that its wasni't pumping water? No tell tail?
What did the old thermostat look like? Do you think pieces of rubber might have broken off the old impreller?

I had to replace the thermostat in a 90hp Merc. It would never close all the way so the motor ran too cool and wouldn't run right. thermostats do fail.

 

[Sandy-man]

I wasn't with him when it happened but he said he was motoring around the lake for several minutes and when he throttled it to get on plane it just wouldn't respond. He looked back and saw smoke coming out of the motor. Now at home, with the lower unit in a barrel of water, the motor running but no water coming out the pee hole.

 

[Sandy-man]

He hasn't taken the thermostat out yet, but I told him he should order a new one and gasket to replace once he has flushed out the cooling system. We just need to find out how to flush it out.

 

[wn6ngp]

It could be that the riser tube from the water pump to head has come loose somewhere. It doesn't seem likely that something big enough would get sucked in and block things up. Maybe the impeller itself broke apart and clogs things somewhere. With a motor this small I'd think that you could remove lower unit, stand the motor on end and look into that water tube to see how it connects or if something is in it. Do you have a pix of the old impeller?

 

[Sandy-man]

He said the pump he took out still looked good. I just told him he needs to take the lower end back off and look up in there with a good light to make sure it's all intact. I also told him if I was in his shoes I would replace the thermostat and while he has it out, run some water through the openings where the thermostat sits to make sure the water will flow all the way through and out. I'm only guessing because I've never been up against this before.