Overheat Alarm doesn't seem to work..

[apaseman]

I know there are other posts about this, but not one that my ignorant brain could understad...

My key does not beep when I turn it half way, and I have been told that it should. I have a 1987 Champion bass boat with a 1986 Mariner 175 motor. So I am assuming this indicates that my overheat alarm is not working.

Some info. I believe the oil injection system has been turned off and I believe there would also be an alarm for that as well that the original owner disabled, so it may be possible that the overheat alarm is tied to this?

So, if anyone could let me know a few things to look for and possibly where to look I'd truly appreciate it. I've read something about grounding wires to test but I guess I'm such a simpleton that I don't know how to go about doing that :redface:

Thanks for your time, I'm learning a lot working on my boat, and one day hopefully i can return the favor and help someone else in need

 

[Silvertip]

Re: Overheat Alarm doesn't seem to work..

Your not sure the oil injection is turned off????? Are you premixing oil/fuel?? If not, and the engine hasn't locked up I suspect the oil injection is not turned off. The test for the hot a horn is to disconnect the tan wire from the temp sensor on the engine cylinder head. Ground the wire with the key in the RUN position. Make sure you ground the harness end of the wire -- not the sensor end. If the horn doesn't sound it there is a problem.

 

[apaseman]

Re: Overheat Alarm doesn't seem to work..

Sorry, yes I know the oil injection system is not working, I am pre-mixing. I'm not sure if how it's been disabled. Again, with my ignorance, how do I ground a wire? Any tips on where the overheat sensor will be?

 

[sschefer]

Re: Overheat Alarm doesn't seem to work..

Lot's of time this is caused by hooking a stereo up that needs a constant hot to keep the programming. The stereo backfeeds into the accessories (purple lead) and the warning module has voltage on it always. Since it never turns off it never goes through the intial self test beep.

The other thing that happens is that the purple wire (key on accessories) gets wired to the main panel so it's always hot. Again, the purple wire powers the warning module.

 

[Faztbullet]

Re: Overheat Alarm doesn't seem to work..

If the oil injection was properly bypassed and module removed/disconnected, you will not have a beep when key is turned on. To test overheat system, turn key to on, remove cowling and find tan wire on head/s, follow wire to starboard side of engine connection close to behind top of starter, take a piece of wire and ground one end to block and other to phillips screw with tan wires and horn should sound. If not check to seen if horn is disconnected under dash as older motors have a remote horn and is not built into control box.....

 

[apaseman]

Re: Overheat Alarm doesn't seem to work..

Thanks everyone for the responses. I will see what I can figure out

 

[apaseman]

Re: Overheat Alarm doesn't seem to work..

Ok..so I THINK i found the overheat sensor...top of the motor, black box..one set of wires coming out of it..2 purple, one white..or is the white one tan? Anyways, IF this is the sensor, I followed the wire and found where it connects to another part of the motor (where multiple other things are connected), took the white wire (tan?? lol) off, turned the key to on, and touched the white wire to the engine block. No sound.

However, I'm not entirely sure that I found the overheat sensor...but assuming I did, and assuming i did the correct procedure, it seems my overheat sensor is not working. I think i found the "horn" or "bell"...silver thing, looks sorta like one of those bells you'd find on a hotel desk..two wires going into it, under my driver console. I'd assume that it's possible that it could be bad..impossible for me to tell.

Did I do the procedure correctly? If not, what did I screw up? Thanks everyone for your patience!

 

[sschefer]

Re: Overheat Alarm doesn't seem to work..

You should have two black box modules. One is located on the side below the starter and the other on top of the port head. The one on top is the advance module or idle stabilizer whatever they decided to call it that year. The one below the starter is the alarm module.

The temp switch is on the starboard head below #1 cylinder the temp sender (goes to a temp gauge if you have one) is on the port head below #2 cylinder and may or may not be connected to the advance module. During an overheat it is supposed to retard the timing and keep you from exceeding 2000 RPM's. That all depends on what Merc decided to do that year.

The temp switch on the starboard head is what triggers the alarm and is connected through the alarm module. The wiring varies from year to year and some are interconnected. The correct wiring diagram may be tricky to find unless you buy the real Merc Manual.

The first thing I do is get rid of the advance module. I've seen the results when they fail. I also get rid of the the oil tank, remove the oil pump and install a block off plate. I actually do it a little different but for the average guy a block off plate works well.

I run a water pressure gauge and a water temp gauge. I pre mix my fuel and set my timing at 21 degrees to start but usually end up at 24. Since I monitor my temp and water pressure I don't have any need for an alarm that sounds when my engine is already toast so I get rid of that module too.

 

[apaseman]

Re: Overheat Alarm doesn't seem to work..

Wow. Sounds like a good idea, one which I will maybe be able to do one day lol. However, I'm still at the "changing the oil on the lower unit, impeller, T-Stats" stage of motor repair I'm about to give up on this overheat sensor business I'm 99% sure I've found it, but grounding the wire doesn't trip any alarm, and I have no idea how to take this any further with my limited knowledge. I truly appreciate all the reply's!