Mercury OptiMax 150 Overheats - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Mercury OptiMax 150 Overheats

search | FAQ | profile | register | author help

Author Topic:   Mercury OptiMax 150 Overheats

mikeyox posted 06-23-2008 06:48 PM ET (US)
I have a 2003 Mercury OptiMax 150-HP Saltwater Series outboard. I get a warning buzzer when traveling slow. I can run my boat over a hour at cruising speeds with no alarms but as soon as I go slow it comes on. I have replaced the impeller but the problem still is present. The tell tale seems fine, the motor has only 96 hours on it according to the computer diagnotic check. Apparantly, by reading other sites and talking to people there may be a slight blockage creating a pressure and cooling problem at low speeds. Where is a screen located to clean? [Give me] a schematic of the cooling system.
lighten up posted 06-24-2008 09:26 AM ET (US)
A similar problem with my 2005 OptiMax 150 was just resolved last weekend. I have researched the same problem since getting my new Boston Whaler boat last year. I only have 42 hours on my engine and it overheated too many times to think I was picking up trash each time.
The OptiMax 150 ran fine at higher speeds, but at low idle, or when I backed the throttle down to an idle, I got a warning buzzer and the SmartCraft gauge would read "reduce throttle". The temperature gauge would climb to 170 to 200. In addition, my water PSI was too low at 0.09 to 1.5 when idling. The engine would cool as I waited and then start up again. As long as I went fast, it ran good. At low idle or in a no wake zone, the temperature ran high--too high for my comfort.
Everything looked "ok" when I had it winterized last December at the dealer. After taking it out twice this year and getting four alarms, I decided to take it to my old mechanic. Our research indicated it could be a bad thermostat, impeller or most likely the poppet valve. Rather than go through another season of worrying that I might get stranded on a brand new boat, we decided to replace all of the items. My mechanic replaced the two thermostats, impeller (which did look suspect), and the final thing was to check the poppet valve. As it turns out the poppet was fine but the hose leading to it had to take a 90 degree turn in a tight area--it was kinked and one of the three screws that holds the power trim & tilt motor was pushing on it enough to restrict the water flow even further. The hose was replaced with a longer piece and routed differently. Last weekend I ran the boat in a variety of conditions and there was not one alarm! The temperature gauge was running "normal" and everything was great! Thank goodness for my old mechanic. He has made my summer.
jimh posted 06-24-2008 09:49 AM ET (US)
You will probably have to buy the factory service manual to get more details on the cooling system for you motor. That literature is expensive, but it is a good investment if you plan to do any work on your motor yourself.
Generally the only place a screen is located on an outboard engine cooling system is at the water intake on the gear case.
Whenever problems are suspected in the cooling system, a good first step is to service the water pump. Replacement of the water pump impeller and any associated seals is an annual maintenance procedure for some motors.
aussiejake posted 06-24-2008 11:45 PM ET (US)
On the earlier optimax there was a screen on the water flow into the exhaust plate. I doubt whether this would be the problem though as when I removed mine after 650hrs it was clean.
cheers,
Jake
Whalerific posted 06-30-2008 01:44 PM ET (US)
Twin OptiMax 150s on a 25 Outrage do not like the 2500-2800 RPM range with the hull not on plane and will set off the temp alarm.
sosmerc posted 06-30-2008 08:43 PM ET (US)
If your engine ecm doesn't see X amount of water pressure at X rpm it will set off the Guardian System and sound an alarm.
Could be weak impellers or faulty psi sensors. On the other hand, if the poppets are not opening soon enough the temp may get too high at that non-planing speed. In the past on some engines I have reduced the required psi to open the poppets by cutting off a coil or two of the poppet spring.
When replacing impellers, I ALWAYS use the 47-89984T4 impeller...it is a heavy duty impeller. I ALWAYS replace the gaskets on either side of the wearplate. This should be done at the beginning of every season, regardless of engine hours.
Over the LINE posted 07-01-2008 09:42 AM ET (US)
I had the same problem on an older Mariner (Mercury) 150. Two mechanics said it could not be the thermostats but it was. The thermostats and housings were caked with salt. The parts were cheap and changing them was painless.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: Mercury OptiMax 150 Overheats
mikeyox	posted 06-23-2008 06:48 PM ET (US) I have a 2003 Mercury OptiMax 150-HP Saltwater Series outboard. I get a warning buzzer when traveling slow. I can run my boat over a hour at cruising speeds with no alarms but as soon as I go slow it comes on. I have replaced the impeller but the problem still is present. The tell tale seems fine, the motor has only 96 hours on it according to the computer diagnotic check. Apparantly, by reading other sites and talking to people there may be a slight blockage creating a pressure and cooling problem at low speeds. Where is a screen located to clean? [Give me] a schematic of the cooling system.
lighten up	posted 06-24-2008 09:26 AM ET (US) A similar problem with my 2005 OptiMax 150 was just resolved last weekend. I have researched the same problem since getting my new Boston Whaler boat last year. I only have 42 hours on my engine and it overheated too many times to think I was picking up trash each time. The OptiMax 150 ran fine at higher speeds, but at low idle, or when I backed the throttle down to an idle, I got a warning buzzer and the SmartCraft gauge would read "reduce throttle". The temperature gauge would climb to 170 to 200. In addition, my water PSI was too low at 0.09 to 1.5 when idling. The engine would cool as I waited and then start up again. As long as I went fast, it ran good. At low idle or in a no wake zone, the temperature ran high--too high for my comfort. Everything looked "ok" when I had it winterized last December at the dealer. After taking it out twice this year and getting four alarms, I decided to take it to my old mechanic. Our research indicated it could be a bad thermostat, impeller or most likely the poppet valve. Rather than go through another season of worrying that I might get stranded on a brand new boat, we decided to replace all of the items. My mechanic replaced the two thermostats, impeller (which did look suspect), and the final thing was to check the poppet valve. As it turns out the poppet was fine but the hose leading to it had to take a 90 degree turn in a tight area--it was kinked and one of the three screws that holds the power trim & tilt motor was pushing on it enough to restrict the water flow even further. The hose was replaced with a longer piece and routed differently. Last weekend I ran the boat in a variety of conditions and there was not one alarm! The temperature gauge was running "normal" and everything was great! Thank goodness for my old mechanic. He has made my summer.
jimh	posted 06-24-2008 09:49 AM ET (US) You will probably have to buy the factory service manual to get more details on the cooling system for you motor. That literature is expensive, but it is a good investment if you plan to do any work on your motor yourself. Generally the only place a screen is located on an outboard engine cooling system is at the water intake on the gear case. Whenever problems are suspected in the cooling system, a good first step is to service the water pump. Replacement of the water pump impeller and any associated seals is an annual maintenance procedure for some motors.
aussiejake	posted 06-24-2008 11:45 PM ET (US) On the earlier optimax there was a screen on the water flow into the exhaust plate. I doubt whether this would be the problem though as when I removed mine after 650hrs it was clean. cheers, Jake
Whalerific	posted 06-30-2008 01:44 PM ET (US) Twin OptiMax 150s on a 25 Outrage do not like the 2500-2800 RPM range with the hull not on plane and will set off the temp alarm.
sosmerc	posted 06-30-2008 08:43 PM ET (US) If your engine ecm doesn't see X amount of water pressure at X rpm it will set off the Guardian System and sound an alarm. Could be weak impellers or faulty psi sensors. On the other hand, if the poppets are not opening soon enough the temp may get too high at that non-planing speed. In the past on some engines I have reduced the required psi to open the poppets by cutting off a coil or two of the poppet spring. When replacing impellers, I ALWAYS use the 47-89984T4 impeller...it is a heavy duty impeller. I ALWAYS replace the gaskets on either side of the wearplate. This should be done at the beginning of every season, regardless of engine hours.
Over the LINE	posted 07-01-2008 09:42 AM ET (US) I had the same problem on an older Mariner (Mercury) 150. Two mechanics said it could not be the thermostats but it was. The thermostats and housings were caked with salt. The parts were cheap and changing them was painless.