Overheating: Muffler the cause?

[uncledom]

It sounds like diminished flow. When you need power and load up the engine you create the most heat and if you don't have full flow through the system that will be the time it over heats. This seems exactly your situation. Check heat exchanger if you have fresh water cooling and exhaust elbow. Those are the most common locations for blockage. The water lift muffler is an empty plastic box with a baffle in it. A critter could be in there dead or alive but I've yet to see a post on it.

 

[woodster]

As I explained in my original post, I already replaced the impeller. And if it were the pump, then why does it not overheat sometimes, like when I run it in calm water? (I looked and saw that raw water was being expelled then.)

woops my bad i did find where you stated that further down in the thread

 

[John R]

It sounds like diminished flow. When you need power and load up the engine you create the most heat and if you don't have full flow through the system that will be the time it over heats. This seems exactly your situation. Check heat exchanger if you have fresh water cooling and exhaust elbow. Those are the most common locations for blockage. The water lift muffler is an empty plastic box with a baffle in it. A critter could be in there dead or alive but I've yet to see a post on it.

So, maybe my next step is to remove the elbow and check it? What do I look for in it and the muffler, other than to see if there's a blockage? (I would imagine that there could be a blockage in the muffler that is not visible, no?)

 

[uncledom]

When you cleaned out the angle piece did you also check and or clean the heat exchange? I know your dying to look in that muffler but I think your going to be disappointed by its simplicity.
http://realitycheck.me/docs/waterliftmuffler.pdf

 

[mz4wheeler]

Did you change your antifreeze? If so, then what TYPE of antifreeze did you use? Premix or non-premix? If you used non-premix, then how much distilled water did you put in? If the answer is none (or little) then THAT is your problem. I learned the hard way that antifreeze does little to cool the engine. It is the WATER cools the engine.

 

[John R]

Did you change your antifreeze? If so, then what TYPE of antifreeze did you use? Premix or non-premix? If you used non-premix, then how much distilled water did you put in? If the answer is none (or little) then THAT is your problem. I learned the hard way that antifreeze does little to cool the engine. It is the WATER cools the engine.

I used premix, but I have another theory:
I just got back from the boat. I ran the engine repeatedly, up to 2300 rpm's (in gear, tied up at the dock). Temperature stayed where it normally is (around 160). I took off the face of the pedestal to look at the temp gauge wires. Everything was fine, as were the wires on the engine. But one thing I did notice: a coolant hose has a small crack in it and seems to leak coolant slowly. I could see it bubbling out a little. So is it possible that air is getting into the coolant side of the cooling system and is having an effect in rough seas, but not in calm water? Is that possible? (In any case, I'm going to replace those hoses, of course.)

 

[Ken Cross]

The crack seems like an unlikely cause, but it sounds like it's time to replace the hose anyway.
Most of the problems that seem to be difficult leaves us banging our foreheads saying "Of course" once we find them.
Always check the simple or most common things first.
Ken

 

[jibes138]

I've heard of hoses on the suction side of the raw water pump collapsing either because the wrong hose or they get old and soft. Make sure they are wire reinforced hoses. Also take the hose off the HX from the pump, put it in a bucket and start it for a minute to see if flow is good. You may need to boil out your HX to improve efficiency.

 

[Bill Roosa]

after reading the whole thread I'd bet it is just an old thermostat. I've seen stuck open, stuck closed and just plain random sticking in an intermiediate position. The later being really hard to diagnose due to it working when the machanic shows up. Just checking it once in a pan of hot water will not always demonstrate the problem. run it through several cycles of hot and cold and watch closely as it opens. ANY sticking or sudden rapid movement is cause for replacement.

 

[John R]

Just wanted to update people and thank them for their thoughts on this issue.
I checked and rechecked the thermostat and it was working fine. (I was going to replace it anyway just in case, until I was told a new one would cost me $75.)
I replaced a couple of coolant hoses, one of which was leaking. My theory is that the coolant got low enough that air got in the system and in rough water it moved around in some way and stopped the coolant from circulating. Anyway, it SEEMS to have fixed the problem.
It's taken me all this time to report back because it took me this long to think (hope) that I've got the problem solved.