2000 SN 196 Overheat Audible Alarm or Buzzer - GT40

[roger2700]

Hi, have only posted a couple times and did not find a thread on this by searching (apologies if there is one).
On a 2000 SN 196 with GT40.
Recently overheated (~230F or greater) with another person driving, I assumed it went to SLOW limp mode as driver thought boat was running out of gas. There was no audible alarm (may have got a alarm light but it was day and not noticed by person driving). I know an audible alarm was not standard this era, may have been optional? I also know if one is familiar with SLOW it would be obvious that the boat went into limp mode and to check the oil and temp gauges. I am trying to set boat up in case other drivers are using boat and unfamiliar with SLOW limp mode. Questions/thoughts on what others may have done.
1. Can a buzzer of some sort be tied into the overheat system so an unfamiliar person driving the boat would stop boat immediately?
I thought of adding a 12v buzzer but am worried about current draw as I chased the wiring from this site's electrical schematics to the ECM. I assume the ECM gets resistance from temp sensor and triggers SLOW limp mode and also sends a voltage to the alarm light. I would hate to fry that circuit by just putting a buzzer in parallel or in lieu of alarm light.
2. The owner's manual states that "if boat is equipped with Audible Alarm Kit and alarm will sound". Is anyone familiar with this kit?
3. What is the proper function of the alarm light. Is it supposed to light with ignition on and then go off when starts? My light is not on in any start sequence (perhaps because it is defective).
4. Boat had a light blue smoke when opened hatch, all seems to run ok but wonder what caused smoke. I changed engine oil in case that was compromised. Is there anything else I might check or do after such an overheat.
5. Changed impeller and temp back at 160F. Old impeller looks like the rubber vanes may have been spinning independently of the core (metal center with the key slot). Looks like rubber vanes have shifted relative to this metal core, see pic and bulge around core. Is this odd? I thought vanes would be destroyed for an overheat. Impeller was 1 year old and marked with Sherwood on rubber (thought Sherwood has a brass core though). Hope this is not another failure mode to worry about lol.
Thanks for any replies

[Peter6000]

The Check Engine light goes on with ignition on and turns off as soon as oil pressure builds (running engine).
Turns back on if low oil pressure or high water temperature occurs.
This is done by 2 switches oil pressure (normal closed opens with oil pressure)
Hight Temp sensor (switch) closes when temp goes above 210 deg or so.
The 2 sensors (switches) are parallel one side connected to ground the other goes to the check engine light.
2nd pin of the check engine light goes to Ignition +.
The line from the sensor to the ECU is not what controls the light, its a input on the ECU to control limp mode.
When in Limp, RPM's are cutt off at 2400 RPM or so and Idle speed goes from 600 to 800 RPM.
Putting a buzzer parallel to the light would work. The sensors (switches) can probably handle 1 Amp or more.
The problem is the buzzer goes off as soon as you turn on ignition just like the light.
You could feed the plus from the fuel pump relay. In this case you would get a short buzz when you turn on the ignition
and may be a short buzz while cranking until oil pressure builds up.
The fuel pump gets turned on by the ecu for 0.5-1 seconds to build up pressure than turns off. It turns back on when engine is cranking and running.
I'm not sure if a spare cable is available from the motor to the dash. You could put the buzzer in the engine compartment.

[roger2700]

Thank you. Great info/thoughts! So if the the buzzer is in engine compartment it seems I have to get a temp switch that closes at 200F or so, find a place in block or ? with a 1/2" hole to install, wire buzzer negative to temp switch and buzzer positive to 12V. I can't think of way to use current thermistor type sensor with a buzzer due to varying resistance of the sensor.

[Tom_H]

That impeller failure you found (where the hub separates from the rubber) is unfortunately somewhat common on different runs of impellers. I've had it happen as well (the one time I didn't put a new impeller in for the spring). The only good part about that type of failure is you don't have to chase down any rubber pieces like you do when they lose the fins.

Regarding the smoke, hard to say, but it's not a bad idea to check your exhaust hoses, as they can be damaged on an overheat. I'd recommend pulling an end off to get a look inside the hoses to make sure the interior lining hasn't blistered up or melted. It's also possible the smoke is some latent oil grease that cooked off on an engine that was a bit hotter than it usually is....

[jpwhit]

The smoke is most likely from the exhaust hoses as Tom_H suggests. On a marine engine, the exhaust system typically overheats before the engine itself when raw water stops flowing. Because of that, I would actually key an alarm off the exhaust system instead of the engine. You'd get the alarm very early in the overheat process that way. Long before the engine started overheating. I've actually wanted to put together a similar alarm for my boats. Especially for the ski club boat where I have the same concern. Lots of people driving the boat that may not pay attention to the gauges or even messages on the screen. And IMO, the built-in alarms let things get too hot before they go off, except on the very newest boats where they finally started monitoring exhaust system temperature.

I think I'll throw together 3-4 for my boats. If you'd like one, PM me your address. You can help me test it.

It would be a temperature sensor that zip ties around the rubber exhaust hose connected to a small microprocessor board that measures the temp and drives a loud buzzer if the temp goes over the set value. If you want one, tell me how much wire you'd need to reach from the exhaust hose to your preferred power connection. What kind of terminals on the end of the power connection wires? Power connection would need to be energized when the key is on. It would only draw a tiny amount of current.

[NautiqueTim]

Keep checking the oil to see if it turns milky. Hope you didn't blow a head gasket.

[roger2700]

Just a follow-up to close out this thread on the alarm and hope it's helpful to others. I wired an alarm parallel to the Warning light. At least on 2000 SN keypad, the first push of Start button powers accessories like stereo (no alarm). The second push of Start button and alarm sounds and light goes On and engine cranks. Alarm and light goes off within a second after start. I do like hearing the alarm during start verify alarm is functioning.
Now I have an alarm for overheat yet am still able to use stereo with no alarm sounding.
- Alarm was "DC 3-24V 90dB Active Piezo Electronic Buzzer" from Amaz.
- Warning light was bad, replaced with "12V LIGHT, ENGINE WARNING / LIMP MODE" from Nautique Parts.
Thanks to all from Planet Nautique for input!
FYI, another thread on GT40 alarm shttps://www.planetnautique.com/vb5/forum/nautique-topics/maintenance-technical-discussion/598836-gt40-alarm-test