Yamaha cooling system help

Glass_On

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Jul 7, 2016
Messages
9
Hi everyone. New to this great forum. I purchased a Glastron with a Yamaha 5.7L sterndrive in September of last year. Winterized it good and just took her out yesterday. After 5 minutes running, I noticed it was overheating. The previous owner changed the seawater pump impeller because he said it sometimes overheated. I removed the pump and impeller parts were in the hose on discharge side. I ordered a new impeller because the one in the pump is just starting to get chewed on the face. Now my question is: after putting a flush attachement on the drive, should water be coming out of the pump inlet hose? I even disconnected the hose at the transom and no water is coming in even with the garden hose full blast on the flush kit. Thanks'
Don
 

Bondo

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Apr 17, 2002
Messages
70,465
Ayuh,..... Welcome Aboard,.... Try back-flushin' from the pump to the pickup to see if it's clear,....

It's abit uphill, 'n abit restricted, but, Ya, ya should get water up through from the muffs,....
 

Glass_On

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Joined
Jul 7, 2016
Messages
9
Well, I did backflush and it's clear from the pump to pickup. I removed the 2 water inlet covers yesterday and made an aluminum set with a fitting so I could plug a garden hose and now, I do get water to the pump. I guess the water passages from the drive to the pump are designed in such a way that they need more pressure than muffs will allow when the engine is not in function. I had the sterndrive off for the winter and before I put it back on, I plugged a garden hose direct in the water tube to flush the motor and temperature never got above 150F on the gages. I just thought that muffs would provide enough pressure for that. Now I know why I could not get anti freeze from my small pump to the engine on muffs for winterization. Thanks'
Don
 

Glass_On

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Jul 7, 2016
Messages
9
Well, its not working like it should. Even with my adapter, water is not reaching the new rebuilt pump. I unhooked the hose at the transom and inserted a garden hose and the engine stays cool. Ran it for 1/2 hour and no overheating so, I guess this means out comes the sterndrive. Could there be something cracked in there for the muffs or the adapter I made to not work? Water is not going to the pump on muffs and with the adapter, it is barely making it out of the plastic nipple at the transom.
Don
 

Glass_On

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Joined
Jul 7, 2016
Messages
9
Removed the SD and put it on the bench. On muff and with water full blast, nothing is coming out of the water outlet. I split the case. There is a 4"water tube in the lower unit and it looks like it was JB Welded in place. Even then no water is coming out of that tube. Is this normal? The seal looks good. What am I missing? I don't want to put it back together without finding the cause of why water is not reaching the pump. Any suggestions!! I tried to upload photos but I guess I don't yet qualify for that.
Don
 

Bondo

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Apr 17, 2002
Messages
70,465
Ayuh,.... Ya gotta find the plugged up spot, 'n fix it, or you could feed the raw water pump with a thru-hull fittin',....
 

Glass_On

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Jul 7, 2016
Messages
9
Thanks' Bondo. There is no plugged up spot. I can see clear through when looking into the water tube. I am just wondering why water is not coming out of it or is it just that this design does not work with muffs and the boat has to be immersed in water. Maybe the pump needs to be primed first. It was working last season. Wondering why it's not working since I took it out of storage.
Don
 

Glass_On

Cadet
Joined
Jul 7, 2016
Messages
9
I decided to put the drive back together. I made sure water came out of the drive before hanging it back on the boat. It did with my adapter but not on muffs. I primed the pump directly through the water intake hose. Once everything was back together, I went and tried it out on the water and she runs like a champ. I have no idea on what was wrong other than the pump needed a prime and to not rely on muffs for this design.
Don
 
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