Why has my water pump failed?

[sly_karma]

Cooling system on '88 Evinrude 40 not working. This engine was submerged at its mooring last summer and was resurrected by family members. I brought it back to the Okanagan a few months later to work on it. Got it running OK after changing out CDI pack. Starts and runs easily and consistently now but not cooling. Got some time to tinker again and went looking.

• installed new impeller
• installed new thermostat - old one was seized open
• ran engine with water/vinegar 4:1 solution. Water now coming out of spitter but only at higher rpm. Engine still overheating.
• re + re lower unit to verify impeller installed in correct direction.
• flushed away vinegar solution with fresh water via ear muffs. Cooling OK now, water seen to be exiting via prop hub. Spits at > 3000 rpm.

My conclusion is there was a salt/crud buildup that was blocking the water passages; this is gone now. But the water pump appears to be not working effectively, since the cooling system only works when it gets assistance from 50 psi city water pressure. The impeller is new and I don't see any obvious scoring or galling in the pump housing. Did seem though that the impeller was fairly easy to remove and replace, usually they are tough to twist back into the housing. I'm planning to buy another and install it anyway. Any other ideas?

 

[Ringo]

I would flush it with regular water until the thermostat opens and then switch to Salt Away just so the stuff gets into the entire circuit. Then fill up a big can with fresh water and let the engine run in it at idle rpm. Check the pee hole for water pressure.

 

[Reel Gone]

Partially plugged water jacket on engine perhaps? What does the water pump housing and lower plate look like, if scored or worn could cause reduced flow in the pump.

 

[GLG]

Here is a way to test your water pump.

There is also a tube that runs up from the water pump to the block that may need a look over. On some outboards they can get corroded and leak causing loss of pressure.

 

[sly_karma]

Thanks @GLG that first video especially worth trying. Although my drive shaft diameter is greater than 1/2" so I'll need to figure out a way to adapt a drill to turn it and test pump function. There did seem to be some blockage in the tube up the leg which I removed using compressed air and probing with a bicycle brake cable. The housing of the water pump doesn't have any serious scoring but I've ordered a full pump kit anyway. Everything is much harder to access when it goes back to its island home, better to replace it all now while it's relatively easy.

 

[sly_karma]

I would flush it with regular water until the thermostat opens and then switch to Salt Away just so the stuff gets into the entire circuit. Then fill up a big can with fresh water and let the engine run in it at idle rpm. Check the pee hole for water pressure.

I had it in the vinegar solution with t-stat removed altogether, but still insufficient water flow for cooling. On the ear muffs it does flow and cool, making me conclude pump malfunction.

 

[gungadin]

Not certain about your motor but most outboards have a pipe that runs from the pump into the block. If yours does, remove the leg, and clamp a hose to that pipe, connect your garden hose and turn on the water. If good flow-- pump. no flow, plugged passages somewhere. Also the tell tale hole could be partially blocked gy a piece of debris from inside the block. Insert a wire or blow it back into the block to see if that clears it.

 

[sly_karma]

Thanks, will try that too. I'm concerned about a possible partial blockage up near the head. The copper pipe that runs up through the midsection transitions at the block via a plastic sleeve. any damage or melting due to overheat there could partly constrict it and the only way to access is a full powerhead removal. Adapting a hose to the pipe is a little easier, def worth a try.

 

[sly_karma]

Spun the drive shaft today with a drill on the lower unit in a tub of water. The impeller I installed only a few weeks ago is limp and providing little to no pressure. Switched to a new one and presto, water everywhere. Decided to install a new pump kit so it's going to island in best condition.

Ran well in the tub and appears to control temp. Still dont understand why the near new impeller had failed. Wasn't worn or melted. Weird.

 

[Oly1]

Glad you found the problem. I hate fixing something with a part that you believe is good. Then having problems and checking everything else, then coming back to the one part you thought was good, only to find out it was the problem all along. Frustrating for sure.

Hope the engine runs flawless for you.

Oly

Spun the drive shaft today with a drill on the lower unit in a tub of water. The impeller I installed only a few weeks ago is limp and providing little to no pressure. Switched to a new one and presto, water everywhere. Decided to install a new pump kit so it's going to island in best condition.

Ran well in the tub and appears to control temp. Still dont understand why the near new impeller had failed. Wasn't worn or melted. Weird.