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wesgardner
08-19-2004, 05:03 PM
Hey All,

There's been plenty of talk recently on wakeboard.com about engine overheats...

How would I know if my overheat alarm works? When I turn my key to "On" nothing sounds...there is a printed circuit board just behind my hour meter that is a piece of rust...this may have been an alarm?

I keep a very close eye on my temp gauge when I'm driving but my wife and others also drive and they may not be quite as diligent.

Any suggestions?

1989 Maristar 240 (being slowly restored/upgraded)

Wes

JimN
08-23-2004, 12:37 AM
On that PC board, is there a round plastic part with a little hole in the center? That may be the sensor/alarm.

Leroy(or anyone else here who has an electronics background) - what do you say we design an overheat circuit here? Maybe something with an adjustible threshold?

wesgardner
08-23-2004, 11:07 AM
Yes, there is a small "can" with a hole in it...so much other stuff has been "altered" by previous owners that I wouldn't doubt if it were merely disabled some way although everything appears to be connected just really badly rusted/corroded. I assume the way the thing is supposed to operate is when you first turn the key it gives you a "beep" that then times out and is only supposed to activate if/when there is an overheat situation? I suppose I could take the impeller out of the intake pump causing the motor to overheat and see if the alarm works...but I don't think I'll do that :noface:

Anyway, any light that can be shed is appreciated...

Wes

Leroy
09-19-2004, 09:01 PM
JimN; Given the consequences when you overheat I can't believe engines don't have a shut down circuit. One little piece of stick, or impeller goes bad, and with the noise in the boat you normally don't see gauges or hear warnings. The circuitry would be so simple, I really can't believe it isn't there, especially for boats. Seems you almost never see a car overheat anymore.

Aftermarket device, ready! Who wouldn't pay $50 to save their engine!

JimN
09-19-2004, 09:47 PM
Cars overheat all the time, just not as often because they have a closed cooling system. On the other hand, if a car isn't maintained, it will definitely overheat. Since boat motors are basically car/truck motors, the manufacturers would never expose themselves to the liability of a boater or motorist whose vehicle shut itself off because of an overheat and the people in it were injured or killed because they couldn't get out of the way of something. Much better to toast the motor than get hurt or die.

Programming an ECM to shut a motor down from an overheat is easy. They would just need to interrupt the fuel pump relay trigger or spark when the temp semsor sees the extreme temperature. Unfortunately, Murphy's Law plays a big part here when it comes to the timing of the shut-down.

You could make an aftermarket device, just be prepared for the lawsuits when people get hurt in a collision, storm, or can't avoid going over a waterfall because they can't get the boat running. You have seen people here who didn't change their oil, impeller or do other routine maintenance when they should have- what makes you think they won't use something like this as a crutch? "It's OK, if there's a problem, the motor will just shut down."

A cast iron motor will tolerate an overheat in many cases. A motor with aluminum heads and blocks won't. Not that it's ever a good thing to do, but that's just the reality of it.

I would rather see a passive raw water cooling system with 2 inlets and closed cooling.

Bert
09-20-2004, 12:25 AM
I assume the way the thing is supposed to operate is when you first turn the key it gives you a "beep" that then times out and is only supposed to activate if/when there is an overheat situation?

I am the only owner of my boat and the overheat alarm has never come on when the key is turned on. the one time the impellor failed it did come on whent the temp guage was at 200 degrees.

JimN
09-20-2004, 12:43 AM
No, you aren't the only one whose alarm hasn't gone off and 200 is about where it should make noise, anyway.

hardycm
09-20-2004, 07:38 AM
Wes,

I have an '88 PS 190 and it has the same thing -- a piezo buzzer that buzzes if the key is on and the oil pressure is low or the temperature is high. You can buy a warning buzzer system from Skidim.com for $40. Its item 1330.

Bert
09-20-2004, 09:50 AM
No, you aren't the only one whose alarm hasn't gone off and 200 is about where it should make noise, anyway.
OK, back to the original question. If it doesn't buzz when the key is turned on, how do you know it will work when needed?

Leroy
09-20-2004, 10:08 AM
I guess you could boil the sensor? Unless JimN knows of a secret test mode.

JimN
09-20-2004, 10:15 AM
The circuit is supposed to activate when the temperature sender's resistance is within a specific range. At key on, it won't see overheat unless it's within this range. The only reason the new motors have a key on buzzer is to confirm that the circuit is working properly and this is easy to do with an ECM- they just assign an output wire to send a voltage to the circuit when they decide that it should. I think yours has four wires going to it, right? 12V+, Gnd and input from the temp sender and maybe fron the oil pressure sender. If this is the case, there's no provision for any other response from this circuit, other than an actual overheat or low oil pressure. That is, if it has the low oil pressure input.

You can test the overheat warning by turning the key on and grounding the lead from the temperature sender. As the sender gets hotter, the resistance goes lower and once it gets low enough, the buzzer sounds. If the gauge shows the correct temperature without you thinking that there's a problem with it, I doubt that you have overheated more than the time your impeller went bad and it actually buzzed at you.

Bert
09-20-2004, 11:30 AM
The circuit is supposed to activate when the temperature sender's resistance is within a specific range. At key on, it won't see overheat unless it's within this range. The only reason the new motors have a key on buzzer is to confirm that the circuit is working properly and this is easy to do with an ECM- they just assign an output wire to send a voltage to the circuit when they decide that it should. I think yours has four wires going to it, right? 12V+, Gnd and input from the temp sender and maybe fron the oil pressure sender. If this is the case, there's no provision for any other response from this circuit, other than an actual overheat or low oil pressure. That is, if it has the low oil pressure input.

You can test the overheat warning by turning the key on and grounding the lead from the temperature sender. As the sender gets hotter, the resistance goes lower and once it gets low enough, the buzzer sounds. If the gauge shows the correct temperature without you thinking that there's a problem with it, I doubt that you have overheated more than the time your impeller went bad and it actually buzzed at you.
Thanks, I was just curious as to how I could test it and you have provided the answer. It does have 4 wires going to it. I don't depend on it but would like to confirm it works.