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Author Topic:   1999 Mercury 135-HP OptiMax: Dummy Light

csj posted 08-12-2010 10:55 PM ET (US)
I'm running a CONQUEST 23 with twin 1999 Mercry 135-HP OptiMax motors. I just noticed a red light sensor for the motor temp coming on intermittingly. Both motors [have strong water flow in their confidence stream], if I may say. Anyone have an idea what the [cause of the red sensor motor temperature light coming on] is.
Liteamorn posted 08-13-2010 06:56 AM ET (US)
If you haven't changed your water pumps in more than two years they may need replacing even if your telltale is showing good flow. My 2005 150-HP Optimax would give me an overheat alarm and I had good flow at the telltale. I changed the water pump and no more overheating. Also check your thermostats.
jimh posted 08-13-2010 09:13 AM ET (US)
If you have a visual indicator of OVER HEAT, you should also be getting an aural alert. Better check the alarm system after you repair the cooling system.
Install a water pressure gauge to monitor the cooling system. A water pressure gauge is the only way to monitor the performance of the water pump. With a water pressure gauge you can compare the readings with the manufacturer's recommended readings. I have a chart for my outboard motor that shows the expected water pressure in the cooling system as a function of engine speed. I don't know if Mercury provides that information. Service the cooling system, and after you get a new pump installed, make your own chart of water pressure versus engine speed. In the future you will know when your water pump is beginning to lose output. Or, just replace it annually as many Mercury outboard owners have to.
csj posted 08-14-2010 05:58 PM ET (US)
Thankyou folks, I will start with new water pumps and thermostats.

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Author	Topic: 1999 Mercury 135-HP OptiMax: Dummy Light
csj	posted 08-12-2010 10:55 PM ET (US) I'm running a CONQUEST 23 with twin 1999 Mercry 135-HP OptiMax motors. I just noticed a red light sensor for the motor temp coming on intermittingly. Both motors [have strong water flow in their confidence stream], if I may say. Anyone have an idea what the [cause of the red sensor motor temperature light coming on] is.
Liteamorn	posted 08-13-2010 06:56 AM ET (US) If you haven't changed your water pumps in more than two years they may need replacing even if your telltale is showing good flow. My 2005 150-HP Optimax would give me an overheat alarm and I had good flow at the telltale. I changed the water pump and no more overheating. Also check your thermostats.
jimh	posted 08-13-2010 09:13 AM ET (US) If you have a visual indicator of OVER HEAT, you should also be getting an aural alert. Better check the alarm system after you repair the cooling system. Install a water pressure gauge to monitor the cooling system. A water pressure gauge is the only way to monitor the performance of the water pump. With a water pressure gauge you can compare the readings with the manufacturer's recommended readings. I have a chart for my outboard motor that shows the expected water pressure in the cooling system as a function of engine speed. I don't know if Mercury provides that information. Service the cooling system, and after you get a new pump installed, make your own chart of water pressure versus engine speed. In the future you will know when your water pump is beginning to lose output. Or, just replace it annually as many Mercury outboard owners have to.
csj	posted 08-14-2010 05:58 PM ET (US) Thankyou folks, I will start with new water pumps and thermostats.