Need not peeing on first season fire up

hotrod53

Chief Petty Officer
Joined
Oct 16, 2009
Messages
508
1977, Merc 500 Thunderbolt….I put a new impeller in at the beginning of last season. Today I fired it for the first time of the season in the river. I typically like to test fire in the river because this Merc doesn’t pee as well on muffs.

The Merc started right up and for the first little bit it didn’t pee at all. After a half of a minute I got a pee bubble out of the tell tale but it never got any stronger. I took it home and I stuck some weed wacker string in the pee hole, I didn’t sense any blockage. I fired it in the muffs in my driveway and I’m getting warm water out of the exhaust, but still no peeing. I even tried putting a few pounds of air into the pee hole, no change. The impeller was new last year, prior to that the impeller was about 7 years old with no issue.

What’s your thought, put it in the river and send it thinking the pee line will clear up, or rip it apart? With warm water coming out the exhaust, it’s got to be getting water.
 

airshot

Rear Admiral
Joined
Jul 22, 2008
Messages
4,334
Was the old impellor in one piece ? Often these come apart and pieces get stuck in the cooling system...
 

hotrod53

Chief Petty Officer
Joined
Oct 16, 2009
Messages
508
The old propeller was in good shape but curved as expected. The motor has run a half dozen times since that impeller was installed.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,312
I doubt you will find a poppit valve.----And there is no thermostat either !
 

stresspoint

Ensign
Joined
Sep 19, 2022
Messages
988
I doubt you will find a poppit valve.----And there is no thermostat either !
okay then no poppit or Tstat in that motor, then it must have a corrosion problem, being such an old motor that would not be out of the question i guess.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,161
Trace the telltale hose to the cylinder head water jacket. Remove the telltale hose at the cylinderhead water jacket. Start her on a flusher device and see if a strong telltale stream comes out of the elbow.
 

OCboat

Seaman
Joined
Apr 26, 2007
Messages
73
Did you figure out your issue? I have the same motor and mine does not pump well on muffs either. It will not pee at idle but if I rev it a little and then back down to idle it will start to pump a little. I haven't had it out on the water in 3 or 4 years and will be taking it out soon.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,312
OCboat----Install a new impeller now.-----A 77 does not have a warning horn or a shutdown feature.----It ( and many have ) will run and destroy the cylinder walls !!!!
 

hotrod53

Chief Petty Officer
Joined
Oct 16, 2009
Messages
508
Did you figure out your issue? I have the same motor and mine does not pump well on muffs either. It will not pee at idle but if I rev it a little and then back down to idle it will start to pump a little. I haven't had it out on the water in 3 or 4 years and will be taking it out soon.m
I pulled the lower unit and replaced the entire water pump. Housing, seals, impeller, everything is new. When I pulled it apart I saw that I had replaced the impeller in 2019, longer ago than I thought, but I’d bet it didn’t have more than 10 runs on it.

It’s all back together but time hasn’t allowed me to test fire it on the muffs yet. I’ll update once I do.
 
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