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Mercury Optimax 150 2004 overheating

snowbird

New member
Motor overheats occassionaly g

Motor overheats occassionaly going from slow speed to plane. Alarm sounds on SmartCraft}. Back off and alarm stops. If I "plow" and build up speed no problem. Seems to happen when slow speed temp gets to around 160. Thermostats have been cleaned. Could it be the impellar or something else?
 
"Dick, been having a read thro

"Dick, been having a read through the service manual and it states that your alarm should sound when the temp reaches 221 degrees (+/- a bit).

Before you blame the impeller, which should be changed at minimum every second year (the book calls for a yearly change or every 100 hours - whatever occurs first), I would check a couple of other items.

Does the water flow from the telltale appear to falter when you get the alarm?

You state that the thermostats are ok, but what about the poppet valves? They need between 4-9 pounds of pressure to open up normally and allow the cooling system to work properly - they could be sticking, leaking, blown etc which could cause the overheat.

Or lastly, you simply could have a bad sensor. The design is cheap, simple and prone to failure - but best to err on the side of caution and assume that it is working right and troubleshoot possible causes..."
 
"Obviously, Merc has a real pr

"Obviously, Merc has a real problem here. I have the same motor, EXACT same problem. After going on the internet a lot, there are many of us with this same problem.
Have you fixed it yet? I replaced Replaced the water pump impeller 2X, both thermostats, and still I have this intermittent problem. At high speed troll, about 1800-2000 rpm, the buzzer will go off, overheat. I can run all day if I am at cruise speed, stop, do whatever, then up to cruise speed again. Only when I am at about 2K rpms for about 10 mins do I get in trouble. HELP>
So, if you fixed, PLEASE help me. rj."
 
"I have a 2003 150 Optimax and

"I have a 2003 150 Optimax and have the same problem. It started in my first season and it always occurred when going through a long, no wake zone. The alarm would sound so I would shut it off the engine and let it sit for a few seconds. I would keep turning the key back on until the alarm did not sound. It never happened when running on plane. The water flow appeared to be strong and the water pressure gauge got up to about 15 PSI at top end speed. Afraid of voiding my warranty, I took it in for service. Of course they could not simulate the problem so they changed the impeller and the thermostats at my expense and to no avail. The next time I was in a long, no wake zone, the alarm went off. I took it back at the end of the season and guess what? They changed the impeller again, and again it did not solve anything. Finally, on the third attempt a year later, the technician found something that seemed to be the real cause of the problem. The dealership had just recieved a new piece of diagnostic equipment. A voltage reading that correlates to the water pressure was low. The spec called for a reading between 1.5 and 3, but the reading on my engine was .8. The technician took a harder look and found a clogged screen under the cow. It definitely seemed to solve the problem for a while. This past season the problem returned, probably because I am a Bass fisherman and am always in very, shallow water. If the problem is that simple, I want to fix it myself, but when I lift the cow off, I can't tell where such a screen would be. My guess is if I could remove the lower cow, it will reveal the plumbing that makes up the water path. I tried to remove the lower cow by unfastening the screws that appear to hold it togehter, but it won't separate and I am afraid to force it. My neighbor works for the shop that worked on the engine, so I asked him to find out from the technician how to correct the problem, but apparently the technician has amnesia and doesn't recall my particular problem. Guess it's time to spring for a service manual."
 
Rick (and others). Too

Rick (and others). Took a look at the service manual and I believe the "screen" that you refer to is probably the strainer screen for the air compressor/fuel rail water supply.

My latest manual covers the 2000/01 models but believe it would also apply to yours. Anyone interested can drop me an email (click my name on the left) and I will send you the section (pdf format) that deals with the cooling system....
 
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