Water circulation

[TriadSteeler]

This was part of a thread I have going on the Boat Resto forum, but my particular question fits better over here.

It is in reference to a 1974 Merc500 (3823131). I have rebuilt the carbs, new plugs, water pump assembly, new internal harness, and fuel hoses.

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Finally got an opportunity to get back to the motor. Hooked it up to a new battery, new fuel tank, and the muffs. After about 3-4 seconds with the choke closed, she fired right up after 10 years dormant and idled like a champ.

Here is my first issue. How long does it take for water to come out of the pee hole. I shut her down after about 15 seconds because I didn't want to burn up the powerplant. Is there any way to flush the cooling system and make sure water is getting into and thru the jacket without running the motor.

I had water coming out from the prop exhaust while it was running and some lazy smoke was coming out of the upper exhaust ports after I shut it down. Before I started it, I made sure that the pee hole was clean at least into the rubber hose that is inside the cowl. I also replaced the entire water pump including the impeller.

 

[OldMercsRule]

Re: Water circulation

Hi, I would use compressed air to blow into the 'telltale' or pee hole hose. Fifteen seconds seems a bit short, (in terms of time). The water pressure from the hose should have filled the block so I would try again after blowing out the hole. Good luck JR

 

[TriadSteeler]

Re: Water circulation

I'll give that a shot. Thanks OMR

 

[emckelvy]

Re: Water circulation

Take note of how much water spills out from around the "muffs" before you start. Right after starting the motor, you should notice that significantly less water is being spilled around the muffs. This would be an indication that water pump is taking up water. Ideally you should have enough water pressure to produce a small amount of water spilling out when the motor's running on the flusher; this ensures the suction side of the pump is completely 'flooded'.

You can get a good idea of how hot she's running by feeling the exhaust manifold outer cover. If there's no water circulation it'll get uncomfortably hot VERY fast!

If it's just lukewarm and never gets more than that you've got water flowing.

Check the temperature of the water spilling out the center of the prop and if it's warm you know that water has passed thru the motor. If it's stone cold there's a 'disconnect' somewhere and the water likely isn't even making it to the powerhead (water tube missed the rubber grommet in the pump, for example).

On the flusher, you'll probably see more water dump down the center section and go out the prop than what will blow out the exhaust relief ports in the upper part of the center section. Once in the water, backpressure will force more exhaust out of the reliefs and also carry more water with.

HTH & let us know how it turns out............ed

 

[TriadSteeler]

Re: Water circulation

Took a drill bit and with a hand drill, completely cleaned out the tell-tale. Fired the engine back up and let it idle for 5 minutes. The exhaust casing and cylinder cover were both slightly warm. Throttled up to probably ~1500-2000 RPM and after about 10-15 seconds got a steady stream from the tell-tale.

That problem solved, it uncovered the next issue. a small amount of water was collecting around the spark plugs and running down the outside of the cylinder cover. I'm guessing that the cylinder cover gasket is shot. Which isn't surprising given that this motor has been sitting 10 yrs.


Couple of questions:

Can that gasked be replaced without removing the powerhead? I'm able to get my Torque wrench to all of the bolts, but are there any hidden issues like removing the bracket that loops over the powerhead.

I'm also considering changing the exhaust cover gasket while I'm at it. Can this also be done with the PH in place?

Are there any other gaskets I should be looking at?