Overheating 454mpi closed cooling system.

B

beachnut

Member
Nov 19, 2009
82
Missouri
Boat Info
410 2000 sundancer
Engines
454 mercruiser
My starboard engine at higher RMP is overheating,and if I bring the RPMs down around 2200 the temp will come back down. I have replaced the sea water pump,the thermostat seams to be fine and my mechanic says my water flows are fine. He says now the next step would be to remove the heat exchanger soak it and flush it out with meratic acid because the boat has been in salt water in its previous life. Has anyone heard of this methode ????? Or what else could be the problem???:smt017

Thanks again in advance for your imput!
Gus
 
Acid flush sounds right. That would have been my 2nd choice right after impeller.

For marine based flush you can use: Rydlyme, Barnacle Buster or Triton Marine Products Engine Flush.

And how did your mechanic check the water flow?
 
That could be the problem. Sounds like you have a restriction somewhere. Other possible locations of the problem would be a restriction at a gear cooler if you have one, or the exhaust risers could have rust build up, therefore not allowing the water to flow properly at higher RPMs.......
 
A rad shop will clean and fix any leaks in your heat exchanger for about $100
If the oil and transmission coolers have never been cleaned you might want to get them cleaned also
 
The mechanic said he removed the hoses to check for obstructions and found none, I am not sure how he checked the flow. He checked the strainers and the though hull grill and said those were clear.He said they swapped he intake hoses and that changed nothing. And also the themostat. He also used a heat detection gun to chech for hot spots. Nothing was said about the risers, and I did wonder about that. We put a whole new water pump and pulley on last month. So he said his next step was the heat exchanger. The boat has been in fresh water for about 2 years now and it ran at about 170 up until last month. Can the risers be cleaned up or do you just have to replace them? I am assuming you can not flush the heat exchanger in place it will have to be removed or can you run a flush product through it in place? He also told me to try a product called water wetter it claims to be able to drop your temp up to 15 degrees. Well this is all I know, and any imput is welcome. Big weekend coming up,hope everything holds up!!!!

Thanks again
Gus
 
I had a collapsing RW hose from the sea valve to the strainer. It only collapsed at higher RPM... I replaced the RW pump twice and cleaned the HEs, before the mechanic found the cause of the over heating. The port engine hose was routed with a bend in it. The Mechanic routed with a lesser bend... This fixed my over heater problem... You may have a similar problem since you have the same engines that are about the same age as mine...
 
Is the sea valve between the sea strainer and the engine,and did you have to have someone in the engine room to detect it. I am going to the lake this weekend and will definitely check on this. Thanks for your input.

Gus
 
Replaced the hose from the sea valve to the strainer.Still hot.I ran a thick wire though all the holles in the trans.Cooler and the oil cooler. Still no change. So the next step is to pull off the heat exchanger and lake it to a radiator shop and have it cleaned. One new thing I did notice, my starboard engine did have some smoke or maybe it was steam coming out of the exhaust port,I sure hope it was steam. That would also subside when it cooled down at lower RPM. Hope I am able to figure this out soon it's bugging the sh*t out of me!!!
All imput is appreciated ,and I will report back my findings.
Thanks
Gus
 
One possible contributing cause to a closed water system to over heat could be too much ethylene glycol mix in your system. Pure antifreeze does not have heat transfer ability of water and could contribute to your over heating.
 
Pull the heat exchanger.

I just went through the same problem.
One engine just ran 10-15 degrees hotter underway.
It seemed normal at idle and lower rpms.
I changed everything, same as you..
Also, did a barnical buster rinse through the motor for 10 hours in a closed loop.
It still ran the same temp!
Finally removed the three year old heat exchanger and blasted it out with water and more acid.
Some paint chips/flakes, that might of been on the outside of the unit seemed to be all I removed.
But, now it runs exactly as it should, never hotter than 170 no matter how hard it runs or quickly I slow down to no wake speeds.

Good luck,
 
I do not know if the engines water pump is original or not.It is not leaking like a water pump does on a car when it is going bad. But that is a good point. Is their any other way to check if the circulating pump is bad???
Thanks for your input!
Gus
 
When I go back in a couple of weeks, I will check the amount of pure antifreeze in the system and if that is ok the heat exchanger is coming off. I will report back my findings.
Thanks for the brainstorming session !!!
Gus
 
I just changed the risers on my engines. They were starting to thin. The engines always smoked when I started them for 5 minutes that has now stopped. I got the exchangers cleaned at a rad shop 3 years ago and again this year. They were a little plugged again. If the risers have not been done in past 3 years you might want to remove them and have a look at them a rad shop will clean them also. I did that last time (3 years ago) and they lasted until this time. Also your hull pick ups could be slightly plugged. my generator was running hot and I back flushed it with a garden hose between the strainer and hull it cooled it down to normal.
 
Well I pulled the end caps off the heat exchanger and it was pretty obvious what the problem was. The gasket at each end of the heat exchanger disintegrated, and was plugging the small holes on each end. That explains the difference in the volume of water coming out of the exhaust ports. Did I say that the mechanic said that I did not have a flow problem!!! It sure feels good when you get it figured out and can easily fix it yourself. Gaskets $15.51 each. If I ever figure out how to put a picture on this thread I will put them up. Thanks again CSR for all your help, what a valuable resource.



Gus
 
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