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Mariner not pumping water

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Harry Burnell

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" Hello, I've got a Marine

" Hello, I've got a Mariner 25M that will not pump water from the thermosat opening with the tsat/cover removed. I've replaced the impeller and checked all passages for blockage, but when I run it in a barrel no water exits. I get some water stream from a hole on the side of the leg near the pump and only bubbling otherwise. Any suggestion? Thanks
Harry "
 
"Harry.... Mariners are not my

"Harry.... Mariners are not my line of expertise but from what you've said, I'd suggest that you leave that thermostat cover off, remove the lower unit, then apply either a water hose or air pressure direct to the water supply tube. If either has a unrestricted flow to that thermostat area, my guess would be that something has been overlooked in the water pump.

Joe
"
 
" Joe, I've done that and

" Joe, I've done that and I get good flow throughout. I notice exhaust coming from the thermostat ports is this normal?
thanks
Harry "
 
"Harry.... Hopefully some othe

"Harry.... Hopefully some other tech with knowledge of your engine will jump in here. I have no idea of the exhaust/water routing of the Mariner engine. Tony probably has the answer to that one.

Joe
"
 
"Harry,

If you observed goo

"Harry,

If you observed good flow when you performed the test that Joe described, you can be sure that the problem is with the pump or the water channel below the pump. Make sure there is no blockage there, and check the screen where the water is drawn into the lower unit. Check the walls of the water channel for cracks.

The base plate of the pump and the gasket underneath must seal properly or you will draw exhaust into the pump. If the top of the casing is worn, you might not get a good fit here. The pump housing must also seal properly on the base plate for the same reason.

I'm assuming that you have a 25 HP Marathon, which is the same as a 15 HP. There is the possibility that you left out two washers when you assembled the pump. There should be a washer above, and one below the impeller. The pump will not work without them.

Make sure the water level in the tank is at least as high as the pump, or the pump might have trouble drawing enough water to prime itself.

If this does not sound like your engine, give us the full model and serial numbers, so we can be sure exactly what you have.

"
 
" Tony, Thank you for respondi

" Tony, Thank you for responding. The stainless steel washers that you mentioned are in place. The flow through all ports/screens is good.
Should I get exhaust from either thermostat port when I run it with the tsat and cover removed?
If not, then is this an indication that the head gasket is leaking combustion into the cooling system? It seems odd that it will lose its prime when I rev it. If the impeller is damaged at all how will this affect the pump operation? What is hiding under the cover on the side of the cylinders? Sorry for posting so many ?s.
Thanks
Harry "
 
Tony it is a 25m Mariner made

Tony it is a 25m Mariner made in Japan.
Harry
 
"Harry,

The cover on the po

"Harry,

The cover on the port side of the engine is covering the exhaust. Water flows through here, cooling the exhaust. If the gaskets or exhaust plate are bad the exhaust could mix with the cooling water. Likewise, if the head gasket is blown, the same can happen.

Usually, if you have either of these problems, you would see water come out of the t-stat port, at least for a while. If the water starts to vaporize, then you will see smoke or water vapor. It can look like exhaust gases even if it is not.

Try removing the lower unit, and attatching a water hose to the water tube again. Start the engine and let it run, with the water running, of course. See if it seems to cool properly. If the exhaust system is leaking into the cooling system, you should notice the cover plate heating up. After turning the engine off, let the water run for a few minutes. If the head gasket is leaking bad enough to cause the problem you described, you should find some sign that water is getting into the cylinders. It should be obvious if you remove the spark plugs and inspect them carefully.

If the impeller is damaged, even slightly, it can have a noticeable effect on the pump output.

Is it possible, that for some reason, the driveshaft is not turning, or that the shaft is not turning the impeller? Just a thought, but I have seen people spend hours looking for trouble in the wrong place, when the actual problem was some silly little thing that had been overlooked.

"
 
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