Merc 470 exhaust problem

[ne7800]

Hi first ime poster (also first time boat owner). I just bought a 1980 4 winns with a mercruiser 470 I/O. I had to replace a lot of parts to get it running, it sat for at least 3 years, once i got it out on the water it would not thottle up and started to get hot it ended up burning a hole in the rubber exhaust tube after the elbow at that point the boat started to run really good but was smoking awful due to the burning rubber so i guess my question is WHY did it get to hot? is there a blockage in the ehaust? or is the fresh water impeller not turning? and what turns the impeller? like i said the boat is a 1980 with a mercruiser outdrive not sure what model

 

[jerryjerry05]

Re: Merc 470 exhaust problem

If it sat maybe you need to replace the impeller .It's in the middle of the sterndrive.Get a good factory manual.There is a guy on e-bay that sells all kinds of manuals on CD.Cheap.Get one and find your outfit.Then study it!!!.It's probably an Alpha drive.Jerry

 

[ne7800]

Re: Merc 470 exhaust problem

every thing i found says the alpha outdrives started around 82 i'm trying to get it running for this weekend i have the new rubber tube and gasket for the elbow if i put a garden hose in the exhaust should'nt just pour out of the prop as fast as it goes in? is there a way to test the impeller without tearing it apart

 

[jerryjerry05]

Re: Merc 470 exhaust problem

R/Mr/Alpha all cool the same.If you hook up the muffs and get water from the exhaust you could be pushing water into the motor.
The only way to check the impeller is to take the hose feed from the back of the motor at the thermo housing off and start it. See how much water is being pummped. It should be a lot!!! Rev it up and see how much more it pumps (even more)If not take the unit apart and check the impeller.Jerry

 

[Bondo]

Re: Merc 470 exhaust problem

is there a way to test the impeller without tearing it apart

Ayuh,.... You already Did that....

The raw water side Isn't moving any water,...
That's Why you burnt up your motor...

 

[gwa584]

Re: Merc 470 exhaust problem

NE7800 -
I agree with the other posts. I'm relatively new to the board but came on for the same reason - turned out my impeller was going and it was enough to burn up that same top exhaust bellow at the elbow. You'll want to remove the outdrive, take it apart to replace the impeller, put it back together and remount the drive. Then check the path from the water hose on the inside. For example, I got lucky because I have a heat exchanger and when I took off just the front end-cap, I found all the missing pieces of my outdrive impeller that had come off. If you don't find them, you run the risk of a serious blockage somewhere that could burn up more bellows.

You should also take a close look around where the exhaust elbow mounts to the manifold (and/or coolant tank, if you have a closed cooling system). Mine showed traces of leaking (from during the high-temp event) so I'm replacing the gasket, which is pretty easy. You'll probably want to do it anyway just to be able to physically get the new inner exhaust bellow on because it's a tight fit usually. If you're a merc mechanic, this can all be done in a few hours probably but for me it was bits and pieces over a few weekends (because I had to learn about the systems first).

 

[ne7800]

Re: Merc 470 exhaust problem

Thanks for all the help i pulled off my lower unit and replaced the impeller (witch by the way was ripped to shreds) i found all the missing peices lower in the out drive where the water comes in. I now have it all bolted back togeather (only took about 10 trys to get he shifter right at least i hope its right) should be giving it a test run tonight. Thanks agian for the help