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Author Topic:   Mercury OptiMax Chronic Alarm Malfunction
fishhead posted 01-13-2007 12:51 PM ET (US)   Profile for fishhead   Send Email to fishhead  
I have twin 2000 Mercury 150-HP OptiMax motors. I have had chronic problems with the block temperature sensor alarm on one engine. It was diagnosed as a bad sensor and replaced. Shortly after the problem began again. All water components were TWICE replaced--pump, impeller, poppet valve, etc.--but the problem continued. I suspect a gauge, wiring, and sensor communication problem. Has anyone encountered a similar problem?
jimh posted 01-13-2007 02:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Implicit in your questions is the assumption that the temperature alarm indications are false, that is, there is no problem with the engine cooling system and that these chronic alarms are a malfunction of the alarm system. If we proceed on that basis, the alarm system itself must be creating an alarm.

The usual temperature sensitive switch used as a temperature sensor in most outboard motors is a normally-open switch. The switch closes when the temperature rises above a threshold. The operation of these can often be tested by partial immersion into heated water. Observe the temperature of the water bath when the contact closes in the temperature sensitive switch. This should confirm the performance of the temperature sensitive switch.

If the circuit is seeking a contact closure (usually to ground) to sound an alarm, you should also look for a stray path to ground in the temperature alarm wiring.

I hope you are talking about convention instruments here, not the SmartCraft upgrade.

bsmotril posted 01-14-2007 01:43 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
If you have marginal batteries or a bad battery terminal connection, it will play havoc with all kinds of intermittent alarms on an Opti. Especially at lower RPMS where alternator output is low and battery drain is high. BillS
fishhead posted 01-15-2007 08:44 AM ET (US)     Profile for fishhead  Send Email to fishhead     
Thanks for both addition to the previously mentioned measures to insure all water related parts are functioning normally, the power head was recently replaced as well due to a bearing sleeve failure. So I am fairly confident this is an electrical/faulty gauge/sensor or connection. I will explore both paths suggested and thanks again...will post results
David1877 posted 01-23-2007 06:04 PM ET (US)     Profile for David1877  Send Email to David1877     
I purchased a new 200HP Optimax in July 2006. I too had alarm problems. A dealer diagnosed problem as a bad thermostat and replaced it. Alarm problem went away for awhile but returned. Took rig in and dealer could not get alarm to sound.

The dealer reset the computer in some fashion and said I am goo to go. We will see in the Spring if problems are corrected.

Merc seems committed to getting it right but it is a significant inconvenience taking the rig in.

A new rig should not be so troublesome.

Merc gave me $50 certificate. Little compensation for lost use and actual cost of physical transport.

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