75 HP Mercury 1994 continous beep problem

[bacchus99]

As soon as I turn the key on I get a continuous beep that never goes off whether I start the engine or not. So we know its not overheating because the engine is still cold. Must be a faulty temp sensor...Anyone know what my next steps should be? I'm not sure where the temp sensor on that motor is or how to change/test it. I have also "heard" the actual horn can "stick" but its in the throttle handle and not sure what to try there. Any help is appreciated!!

 

[Texasmark]

Pop the cowl and look at the rear of the block around where the spark plugs are located. At the upper left should be a little cover with 2 bulges in it, one larger than the other...small thermostat used up to 2500 rpms and the big one the pop off valve, pressure operated high flow valve. Below that you should find a tan or tan with a light blue stripe going into a hole in the water jacket. That's the sensor and it's held in place with one screw. It shorts to ground at 195F give or take tolerancing. To test it, follow that wire back to a bayonet coupling in the wiring harness and pull it loose. If your problem goes away your sensor is shorted.

If you don't have a modulating module in your engine and that doesn't solve the problem your magnet in your oil tank fell off and your sensor thinks your oil tank is empty.

 

[bacchus99]

Pop the cowl and look at the rear of the block around where the spark plugs are located. At the upper left should be a little cover with 2 bulges in it, one larger than the other...small thermostat used up to 2500 rpms and the big one the pop off valve, pressure operated high flow valve. Below that you should find a tan or tan with a light blue stripe going into a hole in the water jacket. That's the sensor and it's held in place with one screw. It shorts to ground at 195F give or take tolerancing. To test it, follow that wire back to a bayonet coupling in the wiring harness and pull it loose. If your problem goes away your sensor is shorted.

If you don't have a modulating module in your engine and that doesn't solve the problem your magnet in your oil tank fell off and your sensor thinks your oil tank is empty.

If the magnet fell off in the oil tank wouldn't the beep be intermittent? I did unplug the sensor on the oil tank and it kept beeping(not sure if that clears the oil sensor from being the problem). The only wire I saw going into the head looks like it was pretty far up in the head and kept in place by a foam or rubber piece. Is that the temp sensor? I looked at it and not quite sure how to get it out without damaging the rubber/foam.

 

[Texasmark]

Get a camera and shoot a picture of the rear of the block looking right at all 3 spark plugs. If you have a modulator module oil will be intermittent beep and OT a constant. Otherwise they are both on the same wire and give a solid alarm. If you unplugged the oil sensor your problem is not oil, it's OT or a short in your wiring usually caused by chafing and connecting with a ground.

 

[bacchus99]

The temp sensor goes from the head to a little screw on the side that terminates with 2 other wires. I disconnected temp sensor but beep continued. It stops when I disconnected the wire going back to the horn in the handle. Does that mean it's the horn?

 

[Texasmark]

"The horn in the handle"? You mean the horn at/ in the remote control that you hear blowing? The horn gets 12v from the key switch in all positions other than OFF on either a red wire with a purple stripe or purple wire....that color denotes switched 12v as compared to solid red which is hardwired/fused to the battery.

To blow the horn you ground the other terminal of it. Unplug your remote wiring harness in the engine on the right (starboard) side of the engine. If the beep stops the problem is in the engine. If it doesn't it's the horn or a short in your cabling from the control area, including in the control if your horn is in the control, to the engine. On some controls, like the Quicksilver Commander 3000 (the one with the big black button for fast idle throttle only) the horn is not in the control but tie wrapped to the wiring harness near the control.

"The temp sensor goes from the head to a little screw on the side that terminates with 2 other wires." Other wires Lt. Blue and tan/tan with lt. blue stripe? If so you don't have a fault modulator module and the blast, if in the engine could be either oil or temp. Personally I'd go with the magnet falling off in the tank. I hear a lot about that problem but never have heard of a bad OT sensor.

 

[bacchus99]

The 3 wires that come together are tan with blue stripe that goes to temp sensor, another tan with blue stripe that goes to remote control (I assume it's going to horn) and a plain tan wire which I forgot to trace where it goes but if i had to guess it goes to the oil tank. If I disconnect the temp sensor completely the alarm still sounds. If I disconnect plain tan wire the alarm still sounds if I disconnect all 3 alarm stops... If I just touch the tan with blue stripe wire that goes to the remote control back to the block the alarm sounds. Does this tell me the alarm is bad?

 

[Texasmark]

No. By touching the tan with blue stripe that goes to the remote back to the block, you essentially simulated a fail condition.

Some engines have a tan wire for a dash mounted analog temp gauge that requires a thermometer to be installed in the block's water jacket....would be a 1'8" brass plug in the upper right corner of the rear water jacket....the one that contains the OT sensor with the wire you mentioned.

Pull your oil tank and look on the rear at the two wires. What's the color and where do they go?

 

[bacchus99]

No Title

Here is a pic of the block and wires. From closest to block the wires are: tan and blue going to temp sensor, middle wire tan and blue going to remote control, and then just plain tan but I forgot to trace it. If I totally take the temp sensor out of the equation it still beeps. If I take both the temp sensor and plain tan wire out of the equation it still beeps. If I take all 3 wires and keep them separate not touching anything the beep stops. I have half a mind to just disconnect the middle tan and blue wire and stop the beep. If it is only a low oil sensor in the tank i'll never let that happen and if the temp is based on the water stream that is sprayed out the head that is easy enough to see. I'd like to fix it correctly but if it is only saving against common sense then I don't need it.

 

[Texasmark]

In pic #1, Just below plug #2 and almost to the left edge of the water jacket cover we are looking at is the temp sensor with a black plastic shield/sleeve over the tan or tan lt.blue stripe wire coming right out the back of it. It closes at 195F with tolerances and shorts the wire to the block thus grounding the horn and making it blow. Above it, mounted vertically is the cover for the tstat and pop off valve; stat the smaller of the two bulges. Popoff kicks in at 2500 (serv. manual number) significantly increasing the flow through the block and essentially eliminating the effect of the tstat.

Agree with your comment about oil level and associated sensor wire. That's what I'd do on my personal engine if it happened to me rather than tearing out the tank and chasing the magnet and all that. If I were working on someone elses engine for hire, that would be the norm, but I'm not.

If you pulled the OT wire and it didn't change anything then you ought to be able to reconnect it to the control box wiring harness and you will have that protection after you eliminate the tan wire from the junction.

The Pee/tell tale/water stream comes from your exhaust manifold cover. If you refer to Pic #1 and look at the side of the water jacket cover mentioned earlier in my reply, just to the left of the OT sensor, there is a black hose running up the side of the cover and around to the left side of the engine; the big plate. That's the exhaust manifold water jacket cover and it gets water as long as the engine is turning and there is sufficient water above the top of the water pump for it to pump water to the powerhead. It has nothing to do with the block cooling so don't think that that will sub for an OT sensor. It won't other than if there is none, you know the engine is not getting water and will result in an OT.

Looks like you have a workable solution and it was cost effective.

Mark