Engine runs fine on hose but gets hot on the lake

[CatriderF7]

I was recently talking to a guy who said his boat runs fine on a hose, but everytime he puts it in the lake it starts getting hot. Ive read a few different threads of people having this issue but never saw any concluded with an actual fix. I would assume its a water flow issue somewhere, since running cold/pressurized hose water seems to keep it cool. It must just not be drawing enough on its own. Anyone experience this problem before and find a fix? Is there an area that regularly gets plugged up in the cooling system? My first thought was thermostat but theres probably another tight passage somewhere that could get closed up over time. The engine is a 1989 5.7 mercruiser with an alpha one outdrive

 

[Bt Doctur]

Talk to him somemore and find out if he rev`s it up on a hose. If he does he destroyed the impeller in the lower unit. What happens is the pump has so much suction it collapses the hose cutting off the water.The impeller gets destroyed, the suction stop and the hose pressure flows water thru the engine.
On the water the impeller is no longer capable of supplying water to the engine.
And I wish they would fix the website so these messages stop appearing when posing
There has been a database error, and the current page cannot be displayed. Site staff have been notified.

 

[ihearth2o]

you're right about the pressurized water flow. Also, tap water is probably colder than any body of water that he puts the boat in. He could try replacing the impeller if it hasn't been changed in a while.

 

[rvaughn704]

It is the Impeller in the Foot. The part is very inexpensive. You can change it yourself and save some bucks.

 

[CatriderF7]

The impeller is kind of what i was thinking, but he said he looked at it and it looked fine. Although i guess it could still be worn and not making as much suction. He said its been an ongoing problem for a year or two. He hasnt used the boat because of it and now he just wants to sell it

 

[geneseo1911]

Sounds like an opportunity to buy a cheap boat. The impeller vanes get weak after a while and can't spring back like they should. At that point the pump will still move water, but not enough. When the hose is forcing water to the pump, it seems OK, but when the pump is called on to suck water up on its own, it can't move enough. Impellers should be replaced about every 3 years.

 

[ihearth2o]

If his water pump is any where as near buried in the engine compartment as mine is, there is no way I'd go through the trouble of checking the impeller and not replace it. It's too cheap of a part. After a couple years of non use, it's probably due for replacement anyway. The longer his boat sits unused, the more that rubber will harden, chip off and cause burrs inside the edge of the water pump or worse yet, get sucked up into the cooling system and clog everything up.

 

[CatriderF7]

Yeah Im considering buying it, just dont know if its worth it, ill have to go hear it run. The interior has seen better days it looks like its sat outside uncovered for years. When he said the impeller looked good im pretty sure he was talking about the impeller on the out drive not the water pump on the engine.

 

[sean.deangelis]

I could be wrong on this but: If the impeller is bad it will fail to draw water up from the lake into the cooling system. The water pressure from the tap-to-hose-on-rabbit ears is usually enough to circulate water through the block with help from the engine mounted water pump despite the bad impeller. So, even if you could lower the outdrive into a large tub of cold tap water it would still probably overheat because the impeller's failure to draw water up.

 

[CatriderF7]

I could be wrong on this but: If the impeller is bad it will fail to draw water up from the lake into the cooling system. The water pressure from the tap-to-hose-on-rabbit ears is usually enough to circulate water through the block with help from the engine mounted water pump despite the bad impeller. So, even if you could lower the outdrive into a large tub of cold tap water it would still probably overheat because the impeller's failure to draw water up.

Thats what I was thinking. But I never thought of using that as a test. I guess a guy could use that method and if the container/tub doesnt drain or lower you'd know it isn't pulling water in

 

[CatriderF7]

I may have found the cause. I went and looked at it a little bit ago. The outdrive is pitted pretty bad, mustve sat in the water for a long time. Even though the hull is nice and white. Maybe its been acid washed. The exhaust bellow is ripped in half and the shifter boot is all cracked up and falling apart. I couldn't see the water pickup hose but I would bet it probably is in pretty bad shape.

 

[ihearth2o]

that's cool but how does this explain not overheating with muffs?

 

[CatriderF7]

Well as I understand it, the water impeller actually makes suction, so if the water intake line is leaking or falling apart maybe the impeller can produce much suction so it cant push the water as hard. Im just kind of guessing here, someone correct me if im wrong. Obviously the intake hose has to be somewhat in tact for the engine to stay running cool when on the hose adaptor

 

[ponchoman]

My boat almost sunk due to a ripped shifter bellows. Maybe sure he/you get that fixed.

 

[ponchoman]

My boat almost sunk due to a ripped shifter bellows. Maybe sure he/you get that fixed.