1980 DT65 new water pump won't pump water.

[noog83]

Hi all,

First time on this forum.
I have a 1980 DT65 that I purchased not running (had electrical problems that I fixed) it was pumping water with the ear muffs on but I thought I would replace the impeller anyway as the motor had been sitting for 2 years.
After replacing the impeller I took it out for a run and it was pumping very little water. I brought it home and put the muffs on and its pumping well, filled up a drum and tried that approach and it's not pumping at all.
I have pulled the gearbox back off and put the hose on to the bottom of the water tube, flows well, no leaks. Thought there may be exhaust pressure leaking into the pump / cooling system somehow but I have pulled the leg off and cannot see any exhaust leaks. I understand how the water pump / cooling system works on outboards but this has me stumped????

[Harper2]

What are your indications that it is not pumping? Does your motor have a way of measuring temp, either actual temp or an overheat light?

Or are you just going by lack of the tell tale stream?

[Solarman]

first check

Ok. New impeller. Any chance something could be blocking tell tale, slide a wire into tell tale to see if any blockage first.

Look at the prop, is the prop lip (back edge of prop) inside the housing of the case? If not, you may have spacer behind prop wrong. There should not be a gap between prop and case.
Next check, all the grommets for the water tube to the impeller housing must seal well enough to keep exhaust out, and water to pump upwards. Also, don't want water to leak out going to the head. So, When you pulled apart, did the water tube stay in place, the top end of tube has a grommet as well, and the tube must be in just right as well, if the grommet there is bad or not in right, it could cause problems. Should be a bolt holding in place, most models, but look up inside with good light to make sure you put it back in just as it comes out, that grommet could be bad as well?

Did you remove the plate on the bottom, under the impeller? That slot in that flat stainless plate is the water passage. Could anything have gotten in the passage that might block the water flow going to the impeller? If the plate is off can you kook down the passage that water comes up through? do you see any blockage, or grommets in the passage? If any grommets in the passage they may be separating the exhaust and water flow passage (why I asked you to look).
When putting the foot back on, must make sure water tube mates with housing and that grommet seals with tube and housing. If grommets are ok, then when putting back together put grommets on lowest part/ edge of tube, so when you push/ bolt together it should seal a far as the bolts pull together. If start with grommet all the way back, there might be small gap in front of grommet.
Hopeful this helps solve your problems, but if not, let us know.

[noog83]

I have checked all components, gromets are in place, there are absolutely no blockages, and yes it is running hot.

[noog83]

There is no water even getting to the pump when I run it in a drum, I know this as there is some melted rubber in the pump housing.
Once I get the leg back on I will check for back pressure coming out of the water tube by putting a balloon or small plastic bag with a rubber band around the tube as I think I have pretty well covered all other possibilities.
Both cylinders are reading 135 psi but I'm thinking there could be a possibility that there is a leak in the head gasket or head thats forcing compression into the cooling system and back in to the pump.
Not keen at all on pulling the head off as I know there is going to be bolts snapping

[Solarman]

melted rubber??

What do you mean melted rubber in the housing?? Did you run the motor, even just spin it over with just the starter, without water on the impeller? THAT'S A BIG NO NO!
If you did that, did the impeller melt, or fragment? Any possibility something lodged in the water pathway?

[noog83]

As I said, it pumps water with the muffs, not in the drum.The melting is from running the motor in the drum for 30sec or so, its not even pulling water to the pump. I would never run the motor without water, and I will say again that there are NO blockages.There is a slight film of melted rubber around the inside of the pump housing, no fragments and no pieces out of the impeller. Just doesn't make sense unless there is a back pressure problem in the cooling system.

[Solarman]

back pressure

It is possible to have the kind of back pressure you're talking about, with the high temps needed to cause the impeller to start melting.
It is NOT the water jacket on the cylinder head.
On one side of your motor there is a plate that covers the exhaust Ports. If the water passages are damaged you can get hot gases from the exhaust blowing back through the impeller and it is hot enough to melt it.

It is generally the port side of the motor, but check parts pages, or manual to be certain.

There are a number of bolts, and many may break off. Be extremely careful, or grind the heads off those that do not come out easily, you will have a better chance getting those bolts out after the cover plate is off if you do this.

Let us know what happens.