temperature alarm going off

[Andrew1]

Hi guys,
The boat is a 1998 Bayliner Ciera 2355 with a 5L Merc. with Alpha 1 drive. It has an aftermarket (Orca) closed cooling system for the engine block only. The problem is the temperature alarm going off over 3000 rpm.
Here are the facts and what I and/or my mechanic have done so far:
The temperature gauge shows between 175F and 180F.
The reading with an infrared gun around the alarm sending unit shows approx. 165F.
If I disconnect the connector from the sender, the alarm does not come off.
Checked the impeller, re-circulating pump, heat exchanger, pressure tested the system, changed the alarm sending unit and the thermostat – 160F, and no problem was found.
I start to suspect that it may not be temperature but an electrical problem, but I am not sure if I understand the system well enough.
My manual shows a normally open one lead alarm sender, but what I have is actually a two lead one. Would it be normally open or closed switch?
Also, the temperature alarm sender seems to be connected to the ICM module – what is the function of this connection and could the ICM module be the problem?
My mechanic is ready to give up on me and I need some help and direction.
Thanks,
Andrew

 

[DJ]

Re: temperature alarm going off

Your temps are NOT hot, especially for a closed system.

I too would suspect a wiring (electrical) issue.

 

[Don S]

Re: temperature alarm going off

That same alarm is also for low oil pressure and low gear oil reservoir.
If the temp is ok, and the oil pressure is ok, and the gear lube is full. Then it's time to disconnect the alarm switchts (Not the gauge senders) one at a time to find the one causing the alarm to come on.
If your mechanic is ready to give up on and doesn't even understand how the alarm system works on a Mercruiser, then If I were you, I would be looking for a new mechanic, cause he doesn't have a clue.

 

[Andrew1]

Re: temperature alarm going off

Thanks guys,
I did disconnect each alarm switch, one by one, and that is how I narrowed the problem to the temperature switch. Replaced it and still have the problem.
Andrew

 

[DJ]

Re: temperature alarm going off

Like i said, your temps's are NOT hot.