Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

Delmarva_Bob

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Jun 4, 2011
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Last fall I had a major service done by my local authorized Merc mechanic - he did whatever is involved including tune-up, filters, plugs, lube, and did the water pump and thermostat. This spring I noticed although the engine starts/runs fine, when I get up to say just before planing speed (about 1500-2000 rpms, probaby about 15-18 mph) the engine wants to overheat - the temp on dash gauge jumps from an idle temp of about 150's up to mid to upper 170s, then the Smartcraft system shuts the engine down and the warning comes on the gauge to reduce engine speed. When I idle back down to say trolling speed (5-6mph) the temp drops - plenty of water comes from the rear indicator spout on back of motor. The other odd thing is if I just gun it and jump from idle up to plane, say up to 3000 rpms or more, 25-30mph, then the temp drops way down to about 110-115. So it appears to be getting plenty of water forced in at speed. At slow idle forward, as I mentioned, it doesn't overheat but it does get up to the 150's which I have heard is normal and no problem. I just don't get this overheating at mid-range - its when your bow starts coming up out of the water and the boats on more or less a sharp angle, upward, just prior to the boat planing off level. If I keep it at that mid-range speed for say 5 minutes or more, with bow up high out of water, then it wants to overheat & shut down. Has anyone had experience with this problem on the Mercury Optimax 2-strokes or have any idea what it could be? I did ask the mechanic - he said the following, which for all I know may be true, but it sounded a bit far-out - he said "sometimes when you replace a thermostat on these motors, it traps an air pocket or air bubble, up under the thermostat area - he then said, just gun the motor from slow idle to wide open a few times and it should knock that air bubble/pocket out of the cooling channel. Just repeating what he said - I have no idea if its true or just some kind of horse-hockey he is telling me - any help is appreciated -
 

storm1982

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Jul 11, 2011
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Re: Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

I have a 05 merc optimax salt water 150 with the same issue. I have had it back to the shop for service and the mechanic acted like he has never heard of it. I am courious to see what kind of imput you recieve.
 

TD_Maker

Chief Petty Officer
Joined
Aug 31, 2005
Messages
564
Re: Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

I had a (1 year old) Optimax 150 on the back of a 21ft SeaPro CC Bayboat. The Mercury was a new motor for me, for I had always had a JohnnyRude since I was a kid. This motor would really scream and run circles around the E-Tecs and Four Strokes outboards out there.

Coming in Sebastian Inlet (a dangerous inlet) during incoming tide and the inlet was raging. I was following the backside of a large wave at about 1/3 to 1/2 throttle. Suddenly, I got a short horn and the motor went into "Safe" mode right in the middle of this rolling inlet. No throttle, no anything. Luckily, another boat was nearby and pulled me into calmer water. The motor cooled and away I went.

I took the motor (under warranty) to a local Mercury dealer. I guess Mercury Optimax has a computer much like an automobile has. The scan showed an overheat in the left bank; consequently, this caused the "hot Horn" and safe mode operation. They replaced the Impeller and that took care of the problem.

Have you seen the impeller on the Optimax? They are very small. The mechanic showed me a comparison between the Honda and Yamaha Impellers, and the Merc is supposed to be much smaller yet be under higher pressure. I read that the impeller should be replaced EVERY year with these motors because they lose their effectiviness.
 

storm1982

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Jul 11, 2011
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Re: Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

Thanks for your insight. I kinda thought that should be the first thing to change, but to hear it from someone else is a plus. I am going to pick up a water pump today I called and they have some in stock. Also I am going to pick up some some new LED nav lights. Once again Thanks.
 

mjhach

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Joined
Aug 3, 2011
Messages
9
Re: Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

Same problem and solution on my 2002 Opti 150HP.
 

storm1982

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Jul 11, 2011
Messages
3
Re: Question on 2004 Mercury Optimax Saltwater 135hp (2 stroke)

This past weekend I changed the impeller, housing and gaskets. Problem is now solved! The issue I found was in the lower gasket. It was torn and moving around blocking water flow to the impeller( so I assume ). Everything in the water pump looked good as new except that lower gasket. Thanks everyone for your input!
 
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