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Discussion Starter #1
Ok, hoping some of you guys can help me out. I've got 2007 Trophy 2352 WA I keep at Copper Kettle in Lorain. About a month ago I was heading out for a day on the lake when my temperature overheat alarm went off. I immediately brought it to neutral and turned the engine off. The temperature was reading about 180 degrees. After 10 or so minutes of cooling off I started it back up and was able to continue the trip. One thing I did notice was when at full throttle the temp started to creep up near 175 but if I kept her just a touch under full throttle (~3800 RPM) the temperature stayed down and I had no problem. Since that episode that is how I've run the rest of the summer.

Fast forward to this week. I went out Monday for the first time in 2 weeks which had been the longest stretch of the summer my boat had seen no action. After leaving the marina I started to throttle up, with the intent of running just under 4000 RPM. Immediately I notice the engine sounded a little labored. Nothing too noticeable if you hadn't been on my boat but enough for me to notice. I'm running about 1/3 throttle and the temp shoots up to 180 within seconds and I shut it off. For the next 30-40 minutes I'm letting it cool off only to restart, throttle up and overheat instantly.

A couple observations while I was out there. If I kept it in neutral and revved the engine to full throttle the temperature did not rise or overheat.

If I let the engine cool and ran at a slow, 2.0-2.5 MPH, the engine did not overheat. Only when I opened up above a slow troll speed did it overheat.

I noticed a very thick, dark green algae build up on the lower unit of my kicker. Much thicker than any growth I have seen yet this summer.

And finally, after it cooled I opened it up to full throttle in an attempt to blow out any build up and could only get up to around 18 MPH. Top speed is low 30's.

I'm looking for any help you guys might have in trouble shooting my problem. And sorry for the long winded post.


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Discussion Starter #3
Ok, thanks. That's one of the first things I thought too. The part that has me scratching my head is the loss of power. Is it possible the thermostat is getting stuck in both the open and closed positions?


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useless poster
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you can take the plastic cover off your lower unit water pickup screen and check to see if something got in there. ak=lso check andy water lines that could colapse from age.
 

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If it's a inboard maybe water pump bearings are getting stiff, or the belts slipping, definitely check the hoses like mentioned a soft hose could suck closed and starve it for water. Water pump in lower unit could be bad if it has one.

If algae is that thick maybe it grew inside and blocking ports in motor but that would have to be some Frankenstein algae.

Check lower unit out of gear, can you turn the prop ok, it may have a bearing problem that's unrelated to cooling and that is what is laboring engine.

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florida ice fishing
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I had a problem something like this last summer. it turned out to be the water line from the outdrive to the transom was leaking and the motor wasn't getting enough water. I would check this water line and put a new water pump in it. I change the impeller every 3 yrs if it needs it or not. yours may have never been changed. if so that could very well be your problem. I didn't see where you said if you have a mercruiser outdrive or a inboard. but if its a mercruiser I would get the kit and change the impeller and the upper housing and the bottom wear plate and use new gaskets. I am 62 yrs old and I can change these in about 1 1/2 hrs. if you want to see how to change it you can google changing mercruiser water pump. or most marinas will change them for less than 150.00. and just guessing I would say this is your problem.

I got mine to hot and ended up having to have a double head gasket job done on my boat. so you really need to get it fixed before running the boat.
Sherman

if a engine is running to hot it will cause it to have a power loss.
 

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Discussion Starter #8
Thanks guys for the replies. Anyone know any good mechanics in the Lorain area? I know the Copper Kettle has a shop but they've been running a couple weeks behind (last time I checked). I would like to have as little downtime as possible with summer winding to a close.


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Discussion Starter #12
Just an update. Replaced the thermostat and gaskets. Ran it for the first time today with similar results. Runs fine (~175 degrees) at idle and below 3000 RPM. Anything higher the temp rises and alarm sounds. So I guess the next stop would be to change the impeller? It's an '07 5.0L 220 HP 305 cu Mercruiser. Is there an impeller on the engine or is it located in the lower unit? Also, the thermostat I replaced was a 160 degree, why am I operating at 175?.


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As Carpetbagger already suggested, replace your impeller. Labor day weekend I took my wife out for a cruise and just happened to pop the hatch while the motor was running and my water pump was leaking a little as was my transmission cooler (I have an inboard) on my starboard engine. My engine wasn't running hot, but the impeller was near shot. Pump replaced and cooler soldered and I am back in action. Next I'll be inspecting my port at haul out. But you should replace your impeller every three years and check out your pump and bearings while your in there.

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I had a similar issue with my 228 mercruiser. Drove me nuts trying to find problem. Ended up being a blockage in the thermostat housing. This is an easy and cheap fix to try(if you haven't tried impeller repairs yet)- get muriatic acid at a pool supply store and soak the thermostat housing for a couple hours in mixture of 50/50 water/muriatic acid. It will dissolve deposits in housing if there are any. I ended up replacing thermostat housing after having to soak each year to remove deposits.
 

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Discussion Starter #15
Well fellas, as it turned out I had a couple problems. Like most of you mentioned, my impeller was bad. What I also found while replacing it was a bad exhaust valve/flapper. I should have that replaced by the morning & be back on the water (hopefully) by tomorrow. Thanks OGF for the help.


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Think about changing the impeller every 2 or 3 years good PM. and the exhaust flapper failed due to the over heat. good fishing bill
 
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