Wiring a water temp gauge.

[Rranger]

I did try looking up the posted diagrams but they won’t open. My motor 1996 merc 125Hp had the heat alarm come on last couple times out. Have checked impeller all good, and replaced the thermostat. Before I hit the water again I want to get a temperature gauge hooked up. My motor presently has this plug in it, I’m not sure what it’s for (first picture) and other pic is a mercury sending unit I’m waiting on, and another pic of the brown wire at the engine coming from the front that I assume I add to to reach the new sensor I’m putting in the hole the other plug is in? And what is that plug in the first pic used for?

 

[dingbat]

How do you know it over heated?

If you got an alarm the "other" plug is the temp switch that triggered the alarm.

With a temp switch already in place, I prefer a pressure gauge to alert me to the loss of water pressure prior to it over heating.

 

[Chris1956]

Ditto

 

[Rranger]

How do you know it over heated?

If you got an alarm the "other" plug is the temp switch that triggered the alarm.

With a temp switch already in place, I prefer a pressure gauge to alert me to the loss of water pressure prior to it over heating.

I don't think it overheated only that the alarm went off. Non stop alarm. Shut off motor for a bit end of alarm til it runs some more. So the plug in the engine is for the alarm? In the video below the guy takes it out without explaining what its purpose is. Plus no wires to it, how does it work? And I appreciate your answers to questions probably seen as a little simple on your end. But believe me I have spent some time googling trying to see what that brass plug in my motor does and came up with squat.

 

[Rranger]

 

[briangcc]

From the vid and your pic, that looks like a standard "bolt" used to close the threaded hole up so it doesn't leak. Any sender I've ever seen has a wire running to it as that's how they generally function.

That bronze/brass "bolt" looks very similar to the water jacket plugs I had to pull when winterizing my Volvo (Four Winns) which is why I'm leaning that direction.

My hunch, is there's another sender you're not seeing either under cowling, wiring, plumbing, etc that triggers the overheat alarm.

**Not an expert in any way/shape/form.

 

[Rranger]

Thanks briangcc appreciate that. Now I can remove it and put in my new sending unit. And will look around for the alarm sender.

 

[Rranger]

A couple more questions my third pic shows a tan and a tan/white stripe wire coming off my remote cable at the engine. As they are also coming off the remote control at the front. From what I’ve read the tan wire is for my sending unit to the gauge at the helm. So I run it from the sending unit to connector off remote cable at the engine then from the tan wire off the remote at helm to the gauge S connector. what is the the tan/white stripe wire for?

 

[Rranger]

May have found it on net tan/white stripe goes to trim unit?

 

[Chris1956]

A couple of things. Your motor very likely has an overheat alarm, that is wired to a buzzer in the remote control. The tan/white wire could be for the temp gauge, as those are "pulled out" of the control along with wires for the tach, trim gauge and instrument lights, plus ground.

I do not know if an inline motor has both an overheat switch and a temp gauge sender. You probably need to find a tapped hole to install one. The V6 engines usually have both from the factory.

Finally, a water temp gauge on an outboard is fine, but a water pressure gauge is much better IMO. A pressure gauge requires a NPT fitting with a hose barb on it, as pressure gauges are mechanical.

 

[Rranger]

Chris1956 I am checking out water pressure gauge’s to buy and will probably go that way, but had a couple water temp gauges, sender was cheap so trying that to get to bottom of temp alarm going off.

 

[Chris1956]

Does temp alarm go off at idle speed or at cruise speed? If idle speed overheat, check bottom of impeller for chipping, check/replace thermostat or look for bad water pump housing seals. If overheat is at cruise, poppit valve could be bad.

If that doesn't fix it, there could be some sort of obstruction. Look under waterpump base for clogs/dirt/debris between water inlet holes and water pump base. My old I/O water intakes used to get clogged with barnacles, as it stayed in the water all summer.

If none of that is the issue, check head bolts for proper torque. Check compression to try to diagnose a leaking head gasket.

 

[Rranger]

Goes off at cruise speed. New thermostat just installed, have a leg extension kit so took drive off and checked impellor( was new) its fine. Poppet Valve I changed the diaphragm, rest looked good. And changed installation method of the ext. kit and outdrive to make sure I have a good seal with water tube and impellor, which I know I have now. Just need to install this temp gauge to see if that helps to figure out why alarm is going off at cruising speed. Once I get this temp gauge hooked up (expecting sending unit today) I can take it for a run.