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Runnig Hot Impeller or Circulating Pump

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publicnuisance

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Had the boat out two weeks ago and the warning horn went off, I looked at the gauges and found that the port engine was in fact hot and shut it down but continued on the starboard engine. After the port cooled down I restarted it and figured out that at idle RPM it will get hot but when fuel is applied to bring it up to near 1000 RPM the temp stays down.

My first thought was that the impeller is going. The boat is in a slip and I do not have a trailer so I was wondering how to determine what is going on. Here is what I came up with. I will disconnect the raw water hose from the stat housing and adapt a garden hose to it and turn on the water, then start the engine and wait to see if it gets hot. If it does then the circulating pump or stat is bad, if not then the empeller is bad.

I have run the engine with the raw water hose disconnected for just a few seconds and water did flow from it, just not sure if it is enough. I will of course route that hose overboard for the above test.

Any thoughts? Does my logic seem sound?

Thanks
Nuse
 
not trying to hi jack this thread but my 5.7 mercruiser is doing same thing. heats at idle as soon is i go to plane and start turning the rpms it cools fine. I will be following this thread and of course will post the results of my repair as i also suspect the impeller, again, not trying to hijack just trying to avoid a duplicate thread
 
If it were the t-stat, RPM wouldn't make a difference. Sounds like an impeller to me or partial blockage at the intake on the drive.
 
Thank you for the info now we can help you.

Yes it also can be the t-stat. I know people who change it out every year.

Could also be a partial blockage in the heat exchanger if you have one say in a power steering cooler, or fresh water cooled motor.

Could also be a partial blockage of the risers, when was yours changed or checked last? In saltwater especially in Fl some say 5 years is the max you can get out of them.

You say the boat stays in the water then i am thinking you don't flush after every use. I do but my boat is on a trailer in my front driveway.

Then it could also be a flapper / shutter that fell down and is blocking the exhaust a little.

So in my humble opinion if it were my boat, i would first make sure that there is no blockage at the inlets. Maybe mussels growing in there, or some other blockage.

Then the t-stat, and if not corrected at that point, all the other things mentioned above.

Good luck !
 
Thanks for all the input, alot of good advise there.

Still curious if my test procedure seem like a good way to tell if it needs to come out of the water for repairs or if they can be done in the slip. Not having a trailer makes it an expensive proposition here in middle TN.

I will disconnect the raw water hose from the stat housing and adapt a garden hose to it and turn on the water, then start the engine and wait to see if it gets hot. If it does then the circulating pump or stat is bad, if not then the empeller is bad.

Thanks
 
Where does the long hose go when in comes in from the transom?

Does it first go to a heat exchanger ? If yes then thats is where you disconnect it.

Start the boat and do not put water to the engine you need only 3-5 seconds to see how high the water shoots. Then quick shut off the motor, you will not hurt anything, drive still in the water.

Fresh water boat good.

If you do have a heat exchanger then that could be clogged as well.

Side note: This is a boat site hope i don't get jumped on, but i loved your town when my family took a ride around the country, very nice people, genuinely graceful, and southern hospitality.

We still talk about it.

Post back after the test, we will go from there if there is good water coming in from the drive.
 
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