'95 Merc 150 warning horn problem

pablo1804

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Joined
Jun 14, 2003
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'95 Merc 150 carb type, black, oil injected.<br /><br />I'm having an intermittent horn warning together with a loss of RPM after running at about 4200 RPM for about 10 minutes. When the loss of RPM occurs, the horn makes the beeping sound, but it may be interrupted or disappear after a throttle reduction or reducing to idle. The RPM will not reset after cycling the ignition switch. When I run the engine the following day, it will come up to full power, but the same problem will occur again after about 10 minutes running at 4000 to 4500 RPM. I have changed the pump shaft sensor and reservoir level is correct.<br /><br />Telltale water flow looks good, but I suspect it is a temp problem and not oil related. What I plan to do is hook a premixed tank to the engine (just in case), disconnect the reservoir and shaft sensor leads to the warning module and run it again. If the warning recurs, I think I will have eliminated an oil related source.<br /><br />I have inspected the thermostats and found that they had been gutted by the previous owner and are just there as gaskets. Can anyone please suggest something else I might check before the next run, such as how to check cylinder temp sensors.<br /><br />Any info would be greatly appreciated, as I do not have a manual yet.<br /><br />Thanks,<br /><br />Paul
 

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Mar 25, 2001
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Re: '95 Merc 150 warning horn problem

Welcome to iboats,com.<br />Do not run this engine without the thrermostats in place, as it can severely damage it, by wapring the head,exaust port plates, or crack the block in extremely cool water.<br />If this engine was designed to not require thermostats, the maker would've saved the 5 buks per model for his profits, and rightfully so. They chose to include them.<br /><br />It sounds like you have a worn impeller, or restriction in the block, most often caused by salt corosion or mud injestion. If the telltale is telling, cooling water may be blocked inside from the afore-mentioned restrictions, or pieces of impeller. Is there any paint discoloring or blistering anywhere? This will appear in worse-cases,and if it IS seen, it is probably time for a rebuild (check compression).<br />Impellers should be changed as normal maintainence items, every two seasons, whether they need it or not. They may last as long as 5 years without flying-apart, but the reason the book calls for every two seasons, is to prevent that...Because, when an impeller grenades inside an engine, the pieces can block vital cooling circuit ports, and kill an outboard, at the same time the telltale is squirting.
 
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