Possible to test an impeller???

[rndcomp]

I am having an overheat issue with my 87 Merc 170. As a test, I disconnect the raw water input line to my heat exchanger and then started the engine (with muffs). There was water coming through the line, however, I do not know if this is a valid test of the stern drive impeller. Can anyone offer input to this? The water coming out of the line really had no pressure to it. The next test I want to perform is to turn on the hose (with the engine off) and see if I am just seeing the water being forced from the hose into the line.

Any help is always appreciated.

Thanks!!

 

[Bondo]

Re: Possible to test an impeller???

Ayuh,.......

What you Did with the hose in fact Showed that water Is flowing,......
Try the Same Test on the Hose coming OUT of the Exchanger......
That'll tell you if the Exchanger is Plugged.......

The next test I want to perform is to turn on the hose (with the engine off) and see if I am just seeing the water being forced from the hose into the line.

That'll tell you Nothing.........

 

[Don S]

Re: Possible to test an impeller???

It's impossible to tell from here how much water flow you have, but there isn't a LOT of pressure from the raw water pump.
Start the engine again, and at idle put the hose in a bucket for 15 seconds. You should have a minimum of 3.3 US gallons.

When was the last time the raw water pump impeller was replaced???? Those impellers are only good for 2 years.

 

[rndcomp]

Re: Possible to test an impeller???

How high should the water pressure be coming out of the hose. Should I have it opened all the way up, about half way, or what? I would assume that this would make a difference, but then again, maybe the impeller only passes so much water regardless of the pressure at the intake ports.

My big problem now is that I am not able to get the heat exchange out of the boat. It appears that the u-bolts are rusted and corroded pretty bad. I will keep trying to make it work.

As for when the impeller was last replaced, I just don't know. It is a new (at least to me) boat.

I will run the test that Bond-O suggests and see what happens. One thing that I did notice was that the outside of the heat exchange gets really hot when the engine is running. Wouldn't think that should happen if everything was working OK.

Is there anything else that I shoudl check? Can the riser be at fault. I already swapped out the t-stat.

Thanks!!!

 

[Don S]

Re: Possible to test an impeller???

The volume test should be done with the drive in the water, not on a hose. The pump will put out more water than the hose will deliver.

 

[rndcomp]

Re: Possible to test an impeller???

So here is the latest..... I ran fresh water through the heat exchanger, both the coolant side and the raw water side and saw no problems. I literally pulled the input and output lines, shoved a hose in the input and watched the water come out of the output. I did this for both the fresh and raw water sides. I then pulled off the front end cap of the heat exchanger and saw no particles that could cause a blockage.

I assume that this is good news. However, whenever I hook up the muffs and let it idle for 10-15 minutes, the temp shoots up to 200 degrees. Now, I guess I could have a bad temp gauge, but I felt the input and output lines of the heat exchanger (fresh water side) and I could not feel any difference (granted, this is not a scientific test).

I would assume the next step is to bite the bullet and have the impeller changed. But, is this most likely the cause. I removed most of the coolant hoses and checked for blockage, and everything looked good.

My big concern is that I will get the impeller replaced and still have the problem. But I guess I will have to cross that bridge when I come to it.

Thanks!!!!

 

[bomar76]

Re: Possible to test an impeller???

Bite the bullet?
An impeller is a regular maintence item, and one of the cheapest parts for the boat.
The FIRST thing I would have done was replace the impeller and been done with it.

 

[Don S]

Re: Possible to test an impeller???

An impeller should be the first thing you check when an overheat occures, it's a maintenance type item that should be replaced every other year. Like I asked earlier, when was it last changed.
Here is a link to a site with some info on changing the impeller.
http://www.mercstuff.com/howdoi.htm
Here is a link to the OEM manual you can use for free.
http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf

 

[rndcomp]

Re: Possible to test an impeller???

Don, I absolutely understand and trust your opinion. I am not sure when the impeller was changed last as I have recently bought the boat. I am a little nervous as to changing the impeller on my own since I have yet to gather the necessary gasket sealers, lubricants, etc.... not to mention I don't have a stand for the outdrive. I will get the boat to a mechanic tomorrow to replace the impeller and hopefully this will solve my problems. I have a hard time believing that a mechanic will charge more than 1 hour labor to replace the impeller.

Thanks for everything, and I will post the results later.

 

[Coors]

Re: Possible to test an impeller???

Sorry to add to your misery, but I get so much grief.
On my OMC. the impeller is replaced in ten minutes, without getting wet.
I go hide now.