Melted Tube on Water Pump

[Fishermark]

I have an SEI 106 outdrive (clone of the Alpha 1, first gen). I noticed when I flushed the engine after fishing last time out that there was no water coming from the outdrive.

(Just a quick explanation. I have a 2003 5.7 Mercruiser with a raw water pump attached to the engine with a thru hull pick up. This is the main cooling for the engine. The impeller in the outdrive merely goes up through the outdrive, through the transom assembly and is then routed back through the stern. The only purpose this serves is to cool the outdrive).

Anyway, I noticed it was pumping out water out through the transom while under way - just when I got back to the house did I notice no water coming out while on muffs.

I separated the lower unit from the upper and found the following: The plastic tube which connects the water pipe was melted.

Here's a couple more pictures:

I will be putting on a new impeller, as it is due, but as you can see, the vanes are all intact. What would cause this to happen? More importantly, what should I do to keep it from happening in the future?

 

[Don S]

Re: Melted Tube on Water Pump

You have to have water going to the engine pump and the drive pump. If you just had water attached to the drive, you would not be getting water going into the exhaust system which is what keeps that plastic from melting.
If you were actually running the engine without water to the engine driven pump, then you probably fried the impeller in that pump. Since it's the one that supplies water to the exhaust.

 

[Reel Poor]

Re: Melted Tube on Water Pump

I've never tried it, but can the water pump in the drive be left out since he has a raw water punp on the engine with the thru hull pick-up?

 

[Fishermark]

Re: Melted Tube on Water Pump

Don - When I flush the engine I always put muffs on the outdrive and use a hose in the strainer for the engine:

Reel Poor - I asked Mercruiser if I could simply leave the impeller out of the outdrive with this setup, and they were of the opinion that I should go ahead and circulate the water through the outdrive in order to help cool it. Whether it does or not, I don't know, but I am simply following their advise.

So Don, is this simply a case of the exhaust getting too hot? Like maybe I should check my risers/manifolds for blockage? The engine runs nice and cool and I recently changed the impeller in the engine mounted pump.

 

[Don S]

Re: Melted Tube on Water Pump

Being as it's an 03 model and that it has the Dry Joint style manifolds and risers, I would be a years pay you DO NOT have manifold and riser problems. Taking them apart is not necessary (the riser/manifold gaskets are about $35 each). But yes, your problem is probably simply lack of water. That white tube will melt before there is ever signs of overheat on anything else. From the looks of your engine compartment and your particular raw water strainer, I would bet the gasket on the lid on the strainer is sucking air when the boat is in the water. Since the top is above the water line, you wouldn't see a water leak of any kind. But the pump will suck air and water, probably not enough water to keep the exhaust gasses from melting that plastic part, but not enough to cause an overheat.
Bet that gasket is one of those old cork gaskets too. Which always seemed to leak if you didn't work especially hard to make sure they were sealed completely.

 

[Fishermark]

Re: Melted Tube on Water Pump

Well, assuming a mechanic in Alaska gets a pretty good annual salary, I'm going to assume that's good news regarding my risers and manifolds!
d

The strainer is a nice one - it is a bronze Groco with 1.25" in and out. The lid is heavy bronze with a large o ring sealing it - no cork gaskets.

I looked at the setup again -- it is REAL close to the water line. If it is above the water line, then it is just barely. I know I should "never say never"... but I've never had a problem with it leaking / sucking air before. I've run it like this for the past three years. I will double check the condition of the o ring and hoses, etc, but I also have the hoses double clamped. (Dont want any leaks there!) Any other thoughts as to what it could be?

 

[Don S]

Re: Melted Tube on Water Pump

Who knows, you may have picked up a plastic bag this past season and let things run a little dry for a few seconds (not long enough to show an overheat) which would be long enough if on plane to melt that thin plastic.
You might pull the hoses off the risers and see if they show any signs of burning.
If you push the lower hose down onto the Y pipe, you can pull the elbow and upper hose off the riser without removing the riser from the manifold.

 

[Fishermark]

Re: Melted Tube on Water Pump

Thanks Don.

By the way, on an unrelated note - for my general education. Can you explain what you mean by my manifolds being, "Dry Joint style manifolds and risers"

 

[Don S]

Re: Melted Tube on Water Pump

As you can see in the pictures below, the standard manifolds and risers had passages thru the manifold and riser only 1/4" away from getting into the exhaust. With that small surface, it doesn't take a rocket scientest to see where they wil fail first.

With the Dry Joint system shown below, the gasket surface is the full surface of the manfiold and riser. No chance for water to get into the engine thru a bad gasket or a bit of corrosion on the gasket surface. The water goes thru completely seperate passages.

 

[Fishermark]

Re: Melted Tube on Water Pump

Thanks!

 

[ziggy]

Re: Melted Tube on Water Pump

yer pics are great dons. i've wondered the difference too and that sure explained it real good......

 

[rodbolt]

Re: Melted Tube on Water Pump

two trains of thought on your set up.
the one I normally use is to take the seawater outlet from the drive, on the transome assy, to a thru hull fitting and just blow the seawater back overboard.
that way I am still circulating cooling water through the upper housing.
however I have 2 customers that never could grab the concept that when flushing out of the water you had to supply water to both the outdrive pump and the engine seawater pump or the housings melted. one customer lost 2 uppers due to a melted lower pump housing.
those two boats now have no impeller in the outdrive.
has not seem to hurt them but they also run the quicksilver HP gear lube and it actually gets changed regularly.

 

[Fishermark]

Re: Melted Tube on Water Pump

Hi Rodbolt,
I do understand the concept that BOTH pumps need water to them or they will burn up. I always put water to both when flushing. I'll probably never know the cause of the "water shortage" which caused the melting. I'm going with the bag possibilty....

I currently just discharge the water through the transom and back into the water, but I am thinking about redirecting back onto the outdrive itself - a built in "drive shower" so to speak.