Mercury black max 150hp pee questions

Jackson777

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Joined
Dec 15, 2014
Messages
8
Hi guys. I have an 1984 Mercury black max 150hp motor. It's started doing this thing where it runs great and pees fine. After about 30-45 minutes it quits peeing and looks like it is spraying a high pressure mist out the pee hole. No idea if it's water, steam or smoke because I'm driving it at the time. Let it sit for a while and it goes back to peeing fine. Any ideas? I thought impeller but why would it work fine, mess up and go back to fine? Thermostat maybe? It's confusing but any help is greatly appreciated!!
 

1nebel0

Chief Petty Officer
Joined
Nov 28, 2005
Messages
512
I would check therms, poppit valve just to make sure all of those parts are working correctly...When was the impeller changed? you don't say at what rpm it is peeing etc..more information needed...The impeller is a very small one that should be changed every year..Max two years if you used the motor weekly... Once it takes a set, it loses pumping ability...not having all of the information needed my bet is on the impeller...
 

Texasmark

Supreme Mariner
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Dec 20, 2005
Messages
14,544
I just responded to a similar on "2008 running hot". Check it out for my answer.
 

Dukedog

Captain
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Oct 6, 2009
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3,235
"ANYTIME" ya have an unknown water and/or over heat problem ya change tha complete water pump, check and/or replace t-stats and poppet first thing.....these things are pretty cheap as for as merc parts go.. change one at a time if ya want but start with tha pump stuff, all of it, not just tha impeller.......jmo.
 
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Jackson777

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Dec 15, 2014
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8
Thanks for the advice guys. Impeller was last change is unknown but it's been at least a year if not much longer. It does this "spray" at any rpm. I am mechanically inclined but have no real experience with boat motors. I will research on poppet and t-stats and impeller. I watched a video on YouTube of a guy doing an impeller and the thought of missing a step or not putting on a gasket right makes me nervous. I will research and try to find the t-stats and poppet and see if that will fix things and work my way on to impeller.

Texasmark, I tried the search for that thread but didn't find one by that tittle. Did you say anything dramatically different than what others above have stated?
 

Texasmark

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Dec 20, 2005
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14,544
Thanks for the advice guys. Impeller was last change is unknown but it's been at least a year if not much longer. It does this "spray" at any rpm. I am mechanically inclined but have no real experience with boat motors. I will research on poppet and t-stats and impeller. I watched a video on YouTube of a guy doing an impeller and the thought of missing a step or not putting on a gasket right makes me nervous. I will research and try to find the t-stats and poppet and see if that will fix things and work my way on to impeller.

Texasmark, I tried the search for that thread but didn't find one by that tittle. Did you say anything dramatically different than what others above have stated?

Not but a few posts from you for the latest iteration: 2008 Mercury Running Hot
On 2 strokers, know not about 4s, there are 2 valves: 1 thermostatically controlled up to 2500 rpm set to start opening at 143 F with the engine OT alarm set to 195, and a second larger pressure regulated pop-off that allows improved, non regulated, flow above that rpm...stated number in manual, actuals may vary somewhat on opening rpm. If your pop-off doesn't open you can experience what you are experiencing.

On 2 stroke I engines both valves are under the same cover on the rear of the engine block, easily visible as a bolted on protrusion from the water jacket cover. If you are going to pop the cover you might as well change the stat too while there. On V engines, that I have seen, there is a stat at the top of each bank but the popoff is below the block fed from a hose connected to the top, rear, center, of the block.
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Complete water pumps are expensive. I don't change just to be changing, especially on expensive parts. One year meets a lot of the criteria of a lot of folks on here. Mine went 10 years and was still working fine but figured it was time to do it. It had a set, slight wear but was still keeping a tough enough pee stream to shoot about 1.5" below the water's surface at idle.

Personally I'd do the popoff and stat as they are easy to do for a beginner. Just remember where things were when you took them out. The money you could have put into a water pump will buy you time on the site Seloc www service manual and help you get them changed out correctly the first time. They sell stats and pressure valves on here too.
 

Jackson777

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Dec 15, 2014
Messages
8
Thank you for sharing Mark. Very good information and I appreciate you taking the time to post it. I'm with you on not replacing just for the sake of replacing. I'm assuming the poppet and popoff valve are the same thing. Just based off what I've read and am experiencing my guess, for what it's worth, is the popoff valve. I watched a vid on the t-stats and they look easy to replace. The poppet looked a little more involved and if t-stats don't resolve it I will likely give it a try. Thanks again.
 

Dukedog

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Oct 6, 2009
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3,235
Tex, ya need ta modify tha part 'bout tha hose from tha top of tha block "feeding tha poppet".. that hose didn't even show up till '89 as a relief of sometime "air pockets" in tha water supply.."after" a lotta reg/rectifier over heat problems surfaced.. thus tha reason for 3 different types of poppet design... his has no such hose as with anything pre '89... more water comes from tha block than that hose... justa a little insight for ya..
 
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Texasmark

Supreme Mariner
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Dec 20, 2005
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14,544
Tex, ya need ta modify tha part 'bout tha hose from tha top of tha block "feeding tha poppet".. that hose didn't even show up till '89 as a relief of sometime "air pockets" in tha water supply.."after" a lotta reg/rectifier over heat problems surfaced.. thus tha reason for 3 different types of poppet design... his has no such hose as with anything pre '89... more water comes from tha block than that hose... justa a little insight for ya..
Thanks.
 
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