Water pump ran dry and now overheating

[PensacolaJason]

I ran my new (to me) boat this past weekend for the first time and after about 10 minutes at full throttle a solid alarm rang and wouldn't stop until we shut the motor off. The motor is pumping water through the telltale. After letting it sit for a while we could run the motor just above idle with no alarms, but as soon as i'd give it some more throttle it would sound the alarm. I pulled the thermostats and they look good to me. I pulled the lower unit and it had all kinds of mud and sand in it. The water pump casing looked prettey good and the impeller didn't have any cracks that I could see, but the prongs were definitely bent from use and would not straighten out. I have cleaned it out and am waiting for a new water pump kit.

I do have a confession to make. On Friday night, the night before I took my boat out, I wanted to make sure the motor would start and turn over, but I didn’t want to hitch it up to my truck just to move it over to the hose to put the muffs on it. I figured running it for just a minute without water wouldn’t hurt it. And that is what I did. After doing some research here in the forums, I have found that some people have reported that running without water for just a few seconds can warp the impeller causing it to pump water still, but to the point where it’s not strong enough to keep the motor cool at high RPM’s.

I doubt it’s a coincidence that the boat never overheated before for the previous owner and after I run it for minutes without water it overheats the next day. I rrealize that was a stupid move, but I'm wondering if this might be the contributing factor to my overheating issue.

 

[kbait]

Motor brand/model?

On smaller outboards, when the impeller takes a 'set' (bent fins), it'll normally cool fine at higher rpm's, but fail at low idle. Maybe that's different w/larger motors?

Also strange it'd pump fine out the tell tale when failing/overheating. I'd change out the waterpump/impeller and test, and hope the worn impeller is the issue.

Good luck!

 

[Barramundi NQ]

I once saw a guy with half his family in the boat on the trailer with the brand new boat and engine running for 5 minutes before he put the boat in the water. That was all it took for him to ruin his motor. Because the impeller is a hard piece of rubber inside a housing that is under fairly strong pressure (if you've ever replaced an impeller you'll know exactly what I mean) the tips and blades of the impeller get hot real quick without water. If you did shut your engine down before any internal damage was done you may have dodged a bullet. Step 1 replace the entire impeller housing and impeller. Step 2 test engine on the water again. If no alarms go off you are good to go. This doesn't mean it's all perfect, there may be some damage done to a bearing or 2. You wont know. So be gentle with it for a while. If inboard outboard arrangement, be a good idea to replace your oil too.

 

[PensacolaJason]

Motor brand/model?

On smaller outboards, when the impeller takes a 'set' (bent fins), it'll normally cool fine at higher rpm's, but fail at low idle. Maybe that's different w/larger motors?

Also strange it'd pump fine out the tell tale when failing/overheating. I'd change out the waterpump/impeller and test, and hope the worn impeller is the issue.

Good luck!

It's a 1987 120hp Evinrude (E120TXCUR)

 

[Barramundi NQ]

Outboard 2 strokes dont like to be overheated. Bearing damage can occur and not show up for a while. I'm dealing with a rebuild now due to picking up a plastic bag on my little 30 mariner. Needle bearing went on the bottom piston. Not trying to scare you, it all depends on how long it was running hot from the time the alarm went off and you shut down the engine.

 

[PensacolaJason]

Outboard 2 strokes dont like to be overheated. Bearing damage can occur and not show up for a while. I'm dealing with a rebuild now due to picking up a plastic bag on my little 30 mariner. Needle bearing went on the bottom piston. Not trying to scare you, it all depends on how long it was running hot from the time the alarm went off and you shut down the engine.

I shut it off as soon as the alarm sounded. Although, I was told that the alarm sounds well in advance of a major overheating issue usually.

 

[Scott Danforth]

yep, running without water toasted the water pump.

 

[tblshur]

one of the impeller blades may have come off and lodged in enjine water passage, you will know when you inspect the water pump if you have someone else do it i would want to be present if i were you. good luck hope your enjine is fine.:joyous: