350 (Merc 260) Overheat Issues - please help!

Yea, you can do it with the muff's but you should expect to see some air because the muff's (even the best ones) will have some leakage. But you should still have good press/flow because your hose connection (to the muff's) will have some press. as opposed to the boat being in the water.

This will determine your/our next diag. step.
 
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I had a very similar issue that kept me at dock for 6 weeks. I would suggest a few things that I don't think I saw written above. First, invest in or borrow a heat gun so you can check the temp at at different points of the motor. I had a very expensive one and a cheap one, $20 and they were off by one degree. This way you can shoot your thermostat housing, headers, risers and heat exchanger (if you have one). This will also allow you to verify that your gages are correct. BTW that was my issue. I trusted my gages and I lost 6 weeks of boating.

Additionally, how is the water flow out of your exhaust. If you have strong flow, it's not a pump issue. Then think about checking your risers, manifolds and heat exchangers if you have one.

If you are raw water cooled, the risers and manifolds will need to be replaced roughly every 5 years due to rust.

If you're fresh water cooled, and your impeller broke at some point, some of the rubber from the impeller will go through your water system and potentially clog your flow.

I hope this helps and feel free to follow up with any questions.

Chris
 
This test can be run with the muffs. And as Barrycf said, I bet there's alot more!!! I pulled out 15+ pieces out of mine, not to mention corrosion, algea, and whatever that forms around it. Im gonna keep on trying to think of all the stupid no cost diagnosis you can do without freaking you out with high cost bolt on 50/50 suggestions. Running that test will help me along.
 
...don't you hate when work gets in the way of your life? I will be testing later this week due to uncontrollable interruptions from my job :) :(
 
...but wondering -- could the pieces have made it into the block and gotten stuck there? I am thinking about all the places they could be. I was able to blow pretty freely through the intake hose from the motor side out the outdrive side. can I run a coat hanger or hard line through there to attempt more dislodging?
 
the first real obstruction impeller peices hit, assuming you have power steering, is the power steering cooler. remove the inlet and outlet water hoses, check the inlet side.
 
...not ignoring or forgetting to update; just overwhelmed with work. It's a great problem to have in Michigan :)

I will update when I perform additional diagnoses, and thank you again for the great ideas!
 
BarryCF said:
Don't worry, our "leaders" are working hard to fix this problem...
Click to expand...
Your leaders. I just live here, try not to bring attention to my self and adjust accordingly:grin:
 
UPDATE -

Finally got time to run the flow test. About 2.5 quarts of water came through the hose after approx 15 seconds at 1000rpm. That puts my flow considerably lower than what is expected.

I took the line off and ran water, compressed air, and a coat hanger through it. Seems clear, and I can breathe easily through the line.

Now what?
 
Well that's definitely not enough h2o!! More stuff 2 check. The impellar housing could be cracked or warped due to the overheat. I hope your lower unit is still off, if the impellar and all the gasket and plates are new and installed correctly, that is a start. To test if the impellar housing is not sealing; put the ears on, apply normal water pressure, then put you hand over the steel feed tube. No water should exit from the housing. If that is good, check the gills that the ears go over for blockage.

At least you've isolated it as a water flow problem...it's going to take you starting at the very point of entry(gills) and working your way forward to the engine. You just have to think like water flow for a few hours and physically touch every inch it flows through to find your obstruction.

Lastly- are u sure the mechanic installed the impellar, seals, etc correctly?
 
From last to first...

I am one of those individuals who's never sure someone else did it correctly. I say this since I have trusted multiple people to get me on the water. I gave them all money in exchange for an "It's all better" line. I went to the water to find that it wasn't. Sooooo...I'm not sure.

I believe I will be working on the issue today.

As I said, (from last to first) THANK YOU FOR YOUR HELP! I am overwhelmingly appreciative!
 
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Would this, perhaps, be an issue? Found it in the lower impeller housing tube.

I am going to kill the guy that replaced the old impeller...
 

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Now you know what is blocking your water flow. The question is how much more there is and how far did it travel.
 
It is REALLY hard to mess up an impeller installation, as a marine mechanic, its second nature. I'd go back and make him eat those peices, and get it changed again for free.

Oh wait you had me do it? Just cut the guy some slack jeez hahaha

Glad you found your problem, overheating causes can be a PITA to find
 
I will be taking her out either tonight or tomorrow to know for sure, but all those were crowded in the lower unit at the bottom of the tube that feeds the upper. I don't know how ANY water got through it!

All this time...
 
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