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Merc 2001 150 Optimax overheat only sometime

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robster

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"Uhh, please help. My Merc is

"Uhh, please help. My Merc is giving me fits. 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>"
 
"Rob:
It drives me nuts when

"Rob:
It drives me nuts when that alarm goes off. Bought this boat in Novmber 07. Engine only had 65 hours on it. Has been in and out of the shop since November. Engine under warranty. Have had the impeller, water pump replaced and tstats tested. This didn't solve problem. Tech removed the power head and found that the left side only had one hole for the water while the right side had two. They took pictures and sent to Mercury. They gave me a new power head! Still have same problem!!!!! Tech now has boat again and has checked every thing out. He tells me there is nothing wrong with motor. Said that this motor was not meant to run at around 2000 rpms for any lenght of time. I find this hard to believe! However, if I go from slow to 3000 rpms or more I have no problems. Can back it off to the 2000 range and no problems.

I am going to send a e mail to Mercury and see what they say about all this. If I get an answer will let you know. If you find out anything let me know.
Thanks"
 
"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"
 
To follow up on my overheating

To follow up on my overheating problem. Now running ok. Tech adjusted the amount of water beeing pumped at low rpms. I noticed a difference right away. The temp at low rpms is around 120 and at 3000 rpms is at 95. Not sure how he was able to adjust the amount of water being pumped. Talk to your tech.
 
"Hey, sorry to jump in on your

"Hey, sorry to jump in on your conversation, I was just reading what Snowbird had wrote earlier about a tech telling him his optimax wasnt supposed to be run for any length of time in the 2000 r.p.m range. The tech was telling the truth. The reason for it is this. There is two modes the optimax runs in. Homogeneouss and stratified.
Homogeneous fuel is injected on the intake stroke and dispersed.
Stratified fuel is injected during compression stroke
Simple terms, stratified fuel charge is an ultra lean burn for fuel emissions at low load. So when you run it around the 2000 r.p.m it hasnt changed into the homogeneous fuel stage, so your engine is running extra lean, and more likely to cause damage. Therefor optimax you should either idle, or run at higher r.p.m. They may have fixed this on newer model optimax's I'm not to sure. Anyway i just thought i would throw that in there so you know why he said that.}"
 
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