Overheating Issue....

[Last Call]

The high temp alarm started going off and I shut her down.  Limped backed to the marina and out she came.  We found the outdrive intake full of barnicles on the inside.  Cleaned them out and back in she went.  I was only able to run at 3800 as anything higher and the temp would climb.  Out she came again and we replaced the impellar, back in again.  Dumped her to WOT and on the alarm came again?  I have had 2 guys tell me it could be due to the bay water temp being so high?  I'm not sure I buy that.  Anybody have an idea as what to investigate next?  Motor: 5.7 Mercruiser, RW cooled w/ Alpha 1 Gen 2 drive.  Thanks for suggestions!

[sealife]

I doubt it is the bay water temp, they use these motors in the tropics don't they. 

How about he thermostats? 

[Capt. Carl]

im thinkin thermostat too

[Tacklebox Joe]

i have a mercruiser i/o too. had similar problem.....replace your temperture sender AND Thermostat. if that does not work check your RW hose behind the drive for cracks, leaks or clogs. you would need to pull the drive for this.

[Baitwaster]

I have a Mercruser as well. Do you have a shop manual for your boat? If not get one they are priceless!!! From what little I read about your problem so far It sounds to me like a lower unit or upper impeller problem (not pumping the water to the motor water pump) Like a car you have a water pump that delivers water throughout the engine to keep it cool, but the big difference is..you don't have a radiator that is level with the engine!!! Your lower impeller has to deliver the water up to it!!!And even if it does The engine water pump has to move it through the engine to keep it cool! Both work as one!!! In other words, both have to be 100% or too hot you go!!! I like to run mine a little hot 185 degrees as it saves fuel on the inboards!! Or you might have my first keeper flounder of this season stuck in your thermostat housing!!! LOL

[Baitwaster]

i have a mercruiser i/o too. had similar problem.....replace your temperture sender AND Thermostat. if that does not work check your RW hose behind the drive for cracks, leaks or clogs. you would need to pull the drive for this.

[Maritime Matt]

When's the last time you did Riser's and Manifolds? Very important to do and its required upkeep on i/o's and inboards. Every 3-5 years no doubt should be done. Very critical is how the outdrive pump was installed. They will suck air and the best way to check is replace the water hose going to the motor from the transom bracket inside the boat with a clear one. Start it up and bring the RPM's up over 1500. Check for air bubbles.  Also Merc has an amount of water that it should pump in a given amount of time at a certain rpm. Hose gets held over a bucket, start engine, bring to proper rpm and see what amount of water is pumped. Not sure of the specs right now. As mentioned, check t-stat and sender. Get a infra red temp gun and shoot it at the t- stat housing, riser's, ect.

[L.T.]

Great info from all,  I will just add one thing.  when you dropped the lower unit to change the pump, was the tube( where the top of the  water pump housing  fits into the middle unit ) also checked for barnacle obstructions.  I had zebra musells in mine at one time.  Must have gone through the screen when very young and grew there.

[wb]

I second Matt's suggestion. If the risers and manifolds are more than a few years old they are prolly clogged up.

[Last Call]

I appreciate all the input!  Risers and manifolds were removed, cleaned and repainted in April.  We're changing the thermostat tomorrow after work and taking another shake down run.