New impeller not pumping water?

Lynn · Dec 8, 2024

35hp Johnson just purchased and it wasn't pumping out any water up top.
I put in an entire impeller kit and fired it up only to not get any water out of the top end.
Put new o-rings on the main shaft and a new rubber grommet on the copper water pipe near the lower unit but nothing nearest the engine itself.
Old impeller was really bad so could there be debris up top?
Can I remove the black plastic water spout easily to look for something plugged up or will it just break?
Impeller direction is the same as the old one and I used triple guard grease and anabolic sealant.
I held the copper water pipe with a wire so I don't think I missed the rubber grommet in the impeller housing when I slid the lower unit back in place.
Any thoughts?

Lynn · Dec 9, 2024

Just took it apart again and it looks good to me. The impeller is spinning.
On other forums I see mention of a thermostat housing and suspect that is my issue? The shaft was greased before it was bolted back together but I didn't see any place for an O-rings on it or do I remember taking and old one off of it?
The hard plastic tube that goes over the shaft has O-rings on both ends that are new.
The copper water pipe only has a rubber seal nearest the impeller and nothing at the motor is there a rubber seal missing there?
After the motor is shut off water does dribble out but not much.

Crazyboat · Dec 9, 2024

Lynn said:
Just took it apart again and it looks good to me. The impeller is spinning.
On other forums I see mention of a thermostat housing and suspect that is my issue? The shaft was greased before it was bolted back together but I didn't see any place for an O-rings on it or do I remember taking and old one off of it?
The hard plastic tube that goes over the shaft has O-rings on both ends that are new.
The copper water pipe only has a rubber seal nearest the impeller and nothing at the motor is there a rubber seal missing there?
After the motor is shut off water does dribble out but not much.

I'm replying only so you know others are seeing your post. I have no answer for you but I'm sure someone will come up with some advice.

Mad Dog 2 · Dec 9, 2024

Lynn said:
35hp Johnson just purchased and it wasn't pumping out any water up top.
I put in an entire impeller kit and fired it up only to not get any water out of the top end.
Put new o-rings on the main shaft and a new rubber grommet on the copper water pipe near the lower unit but nothing nearest the engine itself.
Old impeller was really bad so could there be debris up top?
Can I remove the black plastic water spout easily to look for something plugged up or will it just break?
Impeller direction is the same as the old one and I used triple guard grease and anabolic sealant.
I held the copper water pipe with a wire so I don't think I missed the rubber grommet in the impeller housing when I slid the lower unit back in place.
Any thoughts?

What year and model is the 35 Hp Johnson?
Are you running it in a tank or on muffs?
Does the shaft have a key way and key for the impeller?
Was the impeller missing pieces off the vanes?
Is the impeller bronze insert bonded/secure to the rubber impeller?
Some thoughts.

Lynn · Dec 9, 2024

Impeller has a elliptical key in it and I can feel it spinning inside of the housing when I rotate the shaft by hand.
I think the motor is a 1983 Johnson seahorse 35hp.
I pulled the plugs then the thermostat cover and the thermostat is terrible.
I also pulled the squirter out and it's just a push in plug with a rubber tube and it has no restrictions in it.

Lynn · Dec 9, 2024

I am running it on muffs the rectangular type and I have the hard plastic muffs and the rubber type that fit much tighter.

Sea Antsy · Dec 9, 2024

Lynn said:
Impeller has a elliptical key in it and I can feel it spinning inside of the housing when I rotate the shaft by hand.
I think the motor is a 1983 Johnson seahorse 35hp.
I pulled the plugs then the thermostat cover and the thermostat is terrible.
I also pulled the squirter out and it's just a push in plug with a rubber tube and it has no restrictions in it.

how about trying to start it with the thermostat AND the cover OFF.. see if you get sprayed in the face...

Lynn · Dec 9, 2024

I will give it a try in the morning. I didn't even realize these motors had a thermostat until this morning. And the little piece I can't put a name to is called a tell tale online.

flatheadsteve · Dec 10, 2024

Could be a blockage somewhere in a water passage...Could try running weed eater line up through the tell tale as far as you can get it. I've seen a tiny piece of broken off impeller cause similar symptoms. You can also take the thermostat out and put it in boiling water see if it opens and then closes once removed.

Sea Antsy · Dec 10, 2024

PUMP - WATER TUBE - THERMOSTAT - ENGINE BLOCK-- TELL TALE
1/2 split the problem
If you start it briefly with the thermostat OUT and the thermostat housing cover OFF you should get water from the pump sprayed out ....go from there

Lynn · Dec 10, 2024

I boiled the thermostat pictured above and it works correctly despite looking terrible. The tell tale and the rubber hose attached to it have no blockage.
Is there a rubber grommet on both ends of the copper water pipe? I put a new one in the impeller housing but don't see one at the base of the engine.

OldSailor85 · Dec 10, 2024

Lynn said:
I boiled the thermostat pictured above and it works correctly despite looking terrible. The tell tale and the rubber hose attached to it have no blockage.
Is there a rubber grommet on both ends of the copper water pipe? I put a new one in the impeller housing but don't see one at the base of the engine.

Not to be a jerk, but do you have a factory shop manual for the motor?

Get a shop manual and it should answer all your questions.

FWIW, I have been able to find every manual I have needed on EBay or the internet in general.

I perform all my own work, so a manual is a requirement.

Had to pay $100 for one for my GT150, but that's about 30-minutes of labor these days. Well worth the price.

Lynn · Dec 10, 2024

I do not have a manual for this motor.
I purchased the boat and motor less than a month ago and wanted to fire it up to see if the motor was going to be used or replaced. If I keep the motor I will try and locate a manual.
The local Boat Dr lives half a mile from myself but he is closed Saturday Sunday and Monday.
I live on the West Coast so I am 3 hours behind East Coast time.

FuzzyGrub · Dec 10, 2024

A good number of years ago, had a 1977 35HP Johnson. It died prematurely, due to an earlier life in salt water. My memory from working on it is quite faded. I do believe there was a rubber grommet that the copper pipe fits into. Finding a full schematic for your motor should tell you for sure.

Typically, running on muffs, pressurizes the water upto the powerhead, and masks problems with the impeller pump. So, if the pipe is fitted correctly, the water passageways in the powerhead maybe blocked with the remains of the old impeller.

With the lower unit off, and in neutral, you should be able to wrap a strap wrench around the drive shaft and manually spin it fast enough to get water out the top of the tube. Need two people or a makeshift stand that can keep it upright in a big enough bucket.

Lynn · Dec 10, 2024

I am getting ready to give all of this another try.
The copper water pipe has a rubber grommet on it at the impeller housing.
I just wasn't sure if it also had one on the bottom of the powerhead? I pushed it into the powerhead before reattaching the lower unit I just don't remember it going into a second grommet.
Can I run water into the copper water pipe and up into the engine or is that not an option?
I figured I could duct tape a hose to the water pipe before pulling the powerhead off and looking for blockages?

FuzzyGrub · Dec 10, 2024

Lynn said:
Can I run water into the copper water pipe and up into the engine or is that not an option?
I figured I could duct tape a hose to the water pipe before pulling the powerhead off and looking for blockages?

I don't see why not. Seems like a good test to me. You should get plenty of water running out the thermostat housing. Not sure if there is a way, but might try back flushing before that. It might drive the pieces deeper into other cavities.

Mad Dog 2 · Dec 10, 2024

FuzzyGrub said:
I don't see why not. Seems like a good test to me. You should get plenty of water running out the thermostat housing. Not sure if there is a way, but might try back flushing before that. It might drie the pieces deeper into other cavities.

You should be able to hold the end of the garden hose against the thermostat housing opening and back flush the cooling system down and through the water pump supply tube with lower unit disconnected. If you catch the discharged back flushed water you may see trash and bits and pieces of all impellers from the last 41 years.

I had problems with my out board the raw water pump worked well in a tank.
The square muffs with hard plastic cups the water pump could not pull a vacuum and pump water.
I then made sure the muffs were center on the pickup screen and then used bungee cords to squeeze the plastic cups down and seal then it started pumping.

thill · Dec 10, 2024

Make sure the TOP of the copper water tube is in the right hole. If not, you won't get any water into the powerhead.

Lynn · Dec 10, 2024

Well I spent most of the day working on the issue and nothing helped.
The Boat Dr said to leave the thermostat housing off and start it as was posted here and no water came out at all.
He said to leave the screens off so I did that as well and no help.
I pulled the lower unit back off and reversed the impeller direction and that didn't help at all.
The son who works there thinks it's the upper water water pipe grommet but the father had already left for the day so I won't know until tomorrow if he has the part.
I went through several gaskets and keepers today so hopefully he has more in stock for tomorrow.

Is removing the powerhead a big job on one of these motors?
And what parts will I need to put it back together?

Pappy · Dec 10, 2024

Would be good to know the exact model year of this engine as there were some late 70's engines that had a plastic tube near the top of the water supply to the powerhead that was prone to melting after an overheat. From looking at the parts breakdown yours has this as well and is #114 in the schematic. Very possible this is the cause of your issue.
Secondly.....The thermostat on this engine cannot keep the telltale from functioning at all.
Removing the thermostat housing and running the engine will tell you how much volume is being delivered to the powerhead but that is it.

New impeller not pumping water?

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