1994 Mercury 135 hp Blackmax overheat alarm

Joined
Nov 24, 2009
Messages
19
Hi guys,

A quick question for you.

I purchased my boat about 6 months ago and have used it a few times (and had a great time!)

As it says above, it has a '94 135hp Blackmax. I have had the impeller and t-stats changed since buying it and it generally runs great.

I have the usual Quicksilver throttle also.

My question is, should there be a beep either on the throttle of the engine when starting the engine to indicate that the alarms are working? It has never done this, so I'm concerned that they may not be working.

The oil injection system has been disconnected, and I pre-mix, so I wasn't sure if they previous owner may have disconnected the alarms to stop the low oil alarm going off all the time? Is this what is normally done?

Hopefully you can give me some information and tips on this matter!

Thanks again for your time! :D
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 1994 Mercury 135 hp Blackmax overheat alarm

The oil alert goes through a power on self test, and beeps a few times. There is no controls in the overheat alarm except the sensor itself.

Therefore it appears normal to me if the oil alert has been removed.

If you're concerned, just run it without water for a few minutes and see if the alarm sounds.

JUST KIDDING..................:D

There should be a small (klixon )module held into a shallow cavity on one of the heads with 1 wire coming out of it. (If there's one with 2, its the temp gauge sender) Follow that wire, and it should come to a terminal strip somewhere, usually on the starboard side. With the key on, ground that screw with a test wire and the alarm should sound. That tests the alarm itself.

The only way you can safely test the module itself is to take it off, connect it to a meter or test light, and heat it up on the stove in a pan of water. It should short to the frame before the water boils.

Usually the alarm beeper is so wimpy that when yer going WOT with a lily pad wrapped around the LU, you can't hear it anyway. Don't ask me how I know.

hope it helps
John.
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: 1994 Mercury 135 hp Blackmax overheat alarm

Some modules have a test beep at "Key On" and some don't. Merc made them both way's. John's test will tell you if it's working or not and is the only way to be sure. The temp switch is designed to go to ground at 190 degrees. I test it by heating a cup of water to a boil, putting a thermometer in it, dropping the temp switch (still connected) in to it and turning the key on. I watch the thermometer and note the temp that the alarm stops. If it stops +- 5 deg of 190 I call it good.

One thing to remember, this switch is the equivalent of an idiot light. If the temp is comming up fast by the time you react, damage is likely to have already begun occuring. Like John's say's, it only takes a Lilly Pad to ruin your day.
 
Joined
Nov 24, 2009
Messages
19
Re: 1994 Mercury 135 hp Blackmax overheat alarm

Thanks guys!

Have taken it to be looked at today. They are probably going to install a water pressure meter for me, which should solve my worries. They said the same- that by the time you get a warning (or hear it a WOT) that it's probably too late anyway!

Thanks again... I'm sure I'll have more questions for you sometime soon! :D
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 1994 Mercury 135 hp Blackmax overheat alarm

Some modules have a test beep at "Key On" and some don't. Merc made them both way's. John's test will tell you if it's working or not and is the only way to be sure. The temp switch is designed to go to ground at 190 degrees. I test it by heating a cup of water to a boil, putting a thermometer in it, dropping the temp switch (still connected) in to it and turning the key on. I watch the thermometer and note the temp that the alarm stops. If it stops +- 5 deg of 190 I call it good.

One thing to remember, this switch is the equivalent of an idiot light. If the temp is comming up fast by the time you react, damage is likely to have already begun occuring. Like John's say's, it only takes a Lilly Pad to ruin your day.

Don't forget to use a test lead to provide a return ground path from the switch case to the engine block. With one wire, you could burn it up with a torch and the alarm won't sound.

Using a pressure gauge is the best bet. They have a funky pressure pattern you will get used to, and if it varies, go looking into why. It'll warn you early when there's trouble.

hope it helps
John
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: 1994 Mercury 135 hp Blackmax overheat alarm

John's right. I took it for granted that you'd figure that out.
 

Jonezin

Petty Officer 1st Class
Joined
Jun 15, 2009
Messages
200
Re: 1994 Mercury 135 hp Blackmax overheat alarm

I have a 88 merc 135 v6 #B278681.
My family has had this boat since new, now i have it. I did the grounding test nothing happened. I ordered new thermostats and water pump kit(i know that has nothing to do with nothing). I have a leak in the exhaust plate cove got those gaskets ordered. my temp runs 180-190 at 3500 rpm cursing speed. How close to danger am I?

I would like to put in a buzzer, but I'm a little confused. There is only 1 wire coming from the sensor that goes to this screw, how do I do this, do I take that lead off the screw and splice it to the ground for the buzzer. If you have a diagram that would help me a lot.

My dad gave my brother this boat a few years ago and he didn't give a **** about it,I've loved it from day one. So it has mostly sat in his shop. Well this year he pulls it out wont fire he has all kinds of work done to it, carbs rebuilt new stator injector and fuel pumps rebuilt new coils, everything shy of pulling the head. Wont fire, no spark. So he calls me ask me if I want it, hell yes its my dads Sea Ray Servile if for no other reason. I get it check it out change 2 fuses on the motor and one under dash fires right. Aint life sweet.

But I'm worried she running to hot, everything I could fine calls for 140 degree thermostats,40 less then where we at now. water is very hot out the pisser port. What you think?
 

j_martin

Admiral
Joined
Sep 22, 2006
Messages
7,474
Re: 1994 Mercury 135 hp Blackmax overheat alarm

We were talking about testing it.

The overtemp switch has one wire to it. It is clamped to the head in a little depression, connecting the outside case to the head. If it gets to 190 degrees, internally it connects the wire to the case, effectively grounding it to the motor. Follow the wire to a terminal, where it might pick up a parallel circuit from the oil alert circuit, and then through the engine wiring to the control wiring, to the alarm module, and to +12V through the ignition switch.

If you grounded the circuit at the screw and nothing happened, there's something wrong in the wiring or the buzzer. The ignition switch has to be on for the alarm to sound with it wired as it normally is.

If it gets hot, it grounds one end of a buzzer circuit. The other end goes to 12V.

There's another similar module on some engines on the other head with 2 wires coming out of it. That is a resistance temp sender for a gauge.

hope it helps
John
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: 1994 Mercury 135 hp Blackmax overheat alarm

Maybe this will help - #15 is the switch. The terminal block your looking for is normally on the electrical plate above the switchboxes (#14 in the pic). The factory wire on the sensor is just so long so it will be close to the same area.

v6_wire-1.jpg
 
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