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snowbird

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2004 Mercury 150 Optimax. Smar

2004 Mercury 150 Optimax. Smart alarm goes off after running at around 2000 rpms for a while and then slowly increasing the rpms. Says "check engine over heating". If I boost the speed to over 3000 rpms it runs ok. It sounds like there is not enough water being pumped at 2000 rpms to cool it down as you slowly increase the rpms. Is this normal for this engine?
 
"Has the impeller been changed

"Has the impeller been changed yet? if not, it is well due.

An impeller works by displacing water up the water tube to cool the head at lower rpms and uses centrifugal force to pump it at higher rpms - the crossover point will vary.

Your issue could be caused by one of a few things. As mentioned a bad impeller (or one starting to go) could be the issue. You could have a poppet valve that is not opening properly, bad thermostat or even a slight blockage somewhere in the cooling system or even a bad temp sender.

In any event, this is not something you want to ignore. You need to track down the issue or you could possibly end up with a very nice piece of "high tech junk" if an overheat toasts the engine..."
 
Graham:
Impeller was changed

Graham:
Impeller was changed a few weeks ago. Tech is now checking it out to make sure nothing has happened to it in this short time. It sounds to me that there is a slight blockage somewhere. Is there a way to increase the flow of water at the lower rpms?
 
"I've had this problem wit

"I've had this problem with the optimax we changed 2 things at the same time so I can't tell you which it was but here it goes. The problem you are facing is that at that throttle setting there is not enough pressure to open the poppett valve. you'll notice that once you get over that rpm range the poppett valve opens and the motor cools off dramatically. we found 2 things wrong at the same time both dealing with the impellor. First we found every time we replaced the impellor kit we neglected to replace the key. the key seemed worn on the shaft side. it should be flat on the shaft side but it was beveled and if you looked at the drive shaft it seemed there was diamond shaped chattering marks almost like the impellor was hitting a harmonic and chattering. I’d replace the impellor key. Also we noticed the impellor had no top seal on that impellor there is a place for a rubber seal between the top of the plastic housing and the top of the metal impellor sleeve. the seal is not on any of the optimax documentation and merctech said that they are not putting them in the optimax. but the seal does come in the water pump rebuild kit. it's the same water pump for the older 2st carb mercs and they used the seal. If you replace the key and install the seal it will not overheat. If you could do me a favor replace them one at a time. I still do not know which it was. I suspect it was the impellor key. It was visibly worn and I’ve been inside of new opti's that don't have the seal and don't overheat. please email me with your findings I’m very interested

Good Luck,
Kevin
Deep Blue Marine Repair LLC
[email protected]
San Diego, Ca"
 
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