Water pump keeps burning out

[ndyeti]

I have an '85 50hp Merc 4-cylinder 2-stroke. I have replaced the water pump three times. Being a novice at boat motors I chalked the first time up to my lack of knowledge (running dry, which I never did for more than 30 seconds and running through lily pads.).
Here is my problem, when I first start the motor (cold) water comes out of the weep hole just like it is suppose to, but when I start increasing the throttle and running at a nice cruising speed the weep hole starts spitting and steam starts coming out. I just had the water pump replaced for the third time, the local boat motor mechanic once again told me it was running great just needed a water pump. So I headed to the lake for a day of fishing and as soon as the motor got up to operating temp it started spitting water and steaming like a tea kettle.
Does anybody have any idea of what is going on in my motor that would cause a water pump to fail like that.

Thanks for your help.

 

[Bifflefan]

Re: Water pump keeps burning out

(running dry, which I never did for more than 30 seconds.

First, that is 30 seconds to long. Dont do it at all, ever.

When you did the impeller did you do the housing also?

 

[huntin dawg]

Re: Water pump keeps burning out

Sounds to me like your water pump is fine but your exhaust cover gaskets are shot. The symptoms indicate there is water leak in the exhaust cover and you are seeing exhaust gases coming out the pee hole.

You need a new mechanic.

HD

 

[Faztbullet]

Re: Water pump keeps burning out

I sounds as if it might have a warped base or housing, if it got hot enough to melt the wear plate gasket or lower housing I suggest you replace both. What can happen is when you get to speed the base in no longer submerged and sucks air.

 

[ndyeti]

Re: Water pump keeps burning out

Hey Bifflefan,
Thank for the reply. After the first one burnt out I never started it out of water, and yes the housing was replaced all 3 times.

 

[ndyeti]

Re: Water pump keeps burning out

Hey bullet,
Thanks for the reply, I guess I am not quite following you. At higher speeds (over 15mph) my water intakes are still submerged. I do have a stabilizing wings (not sure what the exact name is) that are mounted above the prop housing (is that the lower housing you speak of), could these wings interfere with water intake?

 

[ndyeti]

Re: Water pump keeps burning out

Hey Hunting dog,
Thanks for the reply,you might be onto something there. I replaced the water pump the second time last year and every time I went out (3 times) I could run under 15mph and not have an issue, pump pees like a champ but as soon as I start to get after it the steam (exhaust) starts coming out and the water just spits out. It reminds me of my steam gun at work.

 

[Faztbullet]

Re: Water pump keeps burning out

No the water pump is higher than the intakes, if the gaskets or lower base is defective it can suck air as the midsection is submerged when idling and at slower speeds. When boat is ran faster midsection is out oot of the water and can suck air as no water to seal it. If it was in my shop I would pull the lower unit off and replace the lower pump base and gaskets...

 

[sschefer]

Re: Water pump keeps burning out

No the water pump is higher than the intakes, if the gaskets or lower base is defective it can suck air as the midsection is submerged when idling and at slower speeds. When boat is ran faster midsection is out oot of the water and can suck air as no water to seal it. If it was in my shop I would pull the lower unit off and replace the lower pump base and gaskets...

Ditto... Also, check yourself to be sure the upper cover and cup were replaced. There's a tab that holds the cup in the correct position and if it spun it will will cause reduced water flow.

Oh heck, just order a complete kit for 40.00 and replace everything yourself. It only takes 1/2 hour. Well maybe not the first time but for sure the 10th time

 

[ndyeti]

Re: Water pump keeps burning out

The first time I replaced it I did the complete kit. I thought I messed something up so the second time I had a mechanic check it out and he told me it just needed a new water pump, which he replaced last year. I had the boat out 3 times last year after he replaced the pump. I could troll and she would pee just fine but at higher speeds it would just spit and steam, basically it seems like its running so hot that the water that is suppose to come out is turned to steam. It even sounds like water hitting hot metal, you can hear it hissing after I shut the motor down.
I called the mechanic today (same guy who has replaced it the last 2 times) and he is thinking my head gasket needs to be replaced.
What do you guys think, should I go else where or keep bringing it to this same mechanic.

 

[sschefer]

Re: Water pump keeps burning out

Yeah, I'm pretty sure I'd find another Mechanic if he's telling you that you need a head gasket... You're engine doesn't have a head gasket, the head is cast into the cylinder. There is a cylinder cover but it won't hurt squat if it's leaking. The exhaust plate on the side of the engine is the most common culprit but rather than try to diagnose it on the internet I suggest you get a second opinion from someone that can be there to see what it's doing.

 

[Wingedwheel]

Re: Water pump keeps burning out

SSCHEFER you are correct, it does get faster dropping the lower unit after ten times. Heck, I'll bet I cut my time down to less than 5 minutes!

 

[sschefer]

Re: Water pump keeps burning out

SSCHEFER you are correct, it does get faster dropping the lower unit after ten times. Heck, I'll bet I cut my time down to less than 5 minutes!

ROFLOL, yeah you tend to get pretty good at it after awhile As a matter of fact, I sucked up a bunch of sand and destroyed the pump on my 150 last week. I had a spare L/U so I just swapped them but I still have to fix it. New kits will be here Wednesday.