Mercury blue band thunderbolt 50hp 1970’s

twony085

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Apr 4, 2022
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Hi I was wondering if anyone could inform me of the best way to clean the water pipe that cools the engine? There seems to be a blockage
 

racerone

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Dec 28, 2013
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38,073
Did your motor over heat ?-----Are you referring to the copper tube from the pump to the engine ?-----Or the tell tale water pump indicator.------You did install a new impeller I hope ?
 

twony085

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Apr 4, 2022
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It did over heat and stall yes. I noticed it wasn’t pumping water out the back of the engine.
 

racerone

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Dec 28, 2013
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38,073
Step #1 is a compression test.-----Post the numbers for #1 , 2 and 3.----Bottom one is harder to do.-----These motors do not have a warning horn or a shutdown system.---They will keep running and destroy pistons / cylinder walls when impeller fails..-------Folks repair / replace water pump impeller when it is too late.----Have you installed a new impeller ?---That needs to be done every 3 years or so.------How did the motor run for you last season ?
 
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twony085

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Apr 4, 2022
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I bought the boat last year, it ran fine and water was coming out the pipe fine. It only happened the once, I’m not sure when the impeller was last changed, I had asked a few companies near me if they’d do it and everyone said no as it’s an old engine….
 

racerone

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Dec 28, 2013
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There simply is no difference between changing an impeller on your motor and a motor that is 10 years old.----Sad when these shops treat folks this way on an ultra simple job !!----Just inspect the impeller .----Do the compression test.------This is a hard lesson to learn for some folks.-----But do the impeller change yourself if compression is good.-----Easy to do and lots of You tube videos to help you.
 

achris

More fish than mountain goat
Joined
May 19, 2004
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27,468
I bought the boat last year, it ran fine and water was coming out the pipe fine. It only happened the once, I’m not sure when the impeller was last changed, I had asked a few companies near me if they’d do it and everyone said no as it’s an old engine….
First rule of buying anything second hand. FULL service before you start using it.... My own boat spent 3 months going nowhere after I bought it. EVERYTHING got serviced/inspected before I put it in the water!

If none of the service companies will do it, do it yourself. Plenty of information on youtube and this forum to help you along the way.

Chris..
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,046
When you drop the lower unit to change the impeller there's a copper tube that leads to the power head, don't pull it out just take a garden hose and send water up the tube; water should come out of the tell tale and out of the driveshaft housing.
 
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