Johnson outboard 15HP 1978. water problem?

Question

Please help. I have 2x exactly the same model Johnson outboard motors 15HP. The one I have just purchased from ebay only pumps small amount of water ( even at high revs )and its in better condition than my original motor( this pumps heaps of water). I have put new impellar in pump, used the hose on the copper water tube to the top and all is fine.lower part of leg has been flushed also. Even put my pump and impellar in the motor from ebay. still the same. I'm frustrated!!!
If you've worked with this model what have I missed ??

Answer 1

Check the thermostat in the head it sound like it's not opening an restricting the water flow. Or exhaust gasket leaking into the water jacket an putting pressure into the water chamber.

Answer 2

1

Answer 3

G'Day JAK,
I have had a couple of these motors, I bought them as 9.9hp and converted them to 15hp they are a very easy motor to work on. I now have twin 50hp Yamaha's on my boat and had a similar problem, one would pump water fine and the other was a very weak stream if at all.I did all that you have done, to no avail then I tasted the water coming out of the tell-tale and it was salty. So I decided to just keep taking bits and pieces off until I found the problem. As it has already been suggested, check the thermostat as mine had a massive buildup of salt and was jammed open only the smallest amount, I removed it cleaned and tested it by placing it in a pot of boiling water so I could see it open, replaced it and it now has a very strong stream from the tell-tale.

Answer 4

15 Hp Outboard

Answer 5

Notice that the impeller is larger than the hole it fits in? When you put it in, you have to rotate it so that the vanes curl enough for it to fall into it's bore.
Here's the part a lot of guys miss: You have to rotate the shaft OPPOSITE normal engine rotation, so that the impeller cups the water while the motor is running & forces the impeller vanes against the bore.. If you curl them backwards, there's enough give in them where they'll pull away from the bore, & let the water get right past them.
I made this mistake myself the first time I changed one.

Answer 6

hi there... have you checked the pin that comes out of the drive and fits in the slot in the inside of the impellor.... it may be worn causing the impellor to basically slip and not spin with the rotation of the drive shaft.
If thats ok.. check the copper tube.. it may have a small hole in it.. also check that it seats firmly into the water pump...it may be leaking there.
now look at the thermostat housing... take out the thermostat and replace it.. if its not opening then the motor wont pee strongly... I had it with an Evinrude 25hp....
If thats ok then there is dirt or rust in the system somewhere..

Answer 7

did you only change the impeller ??? you have to replace the metal "wear plates" around the impeller, they "WEAR" out leaving a gap between the impeller and the metal plates and cup (Reducing water pressure cause water weeps past the vanes and worn plates). Replace the "Whole Pump", you want the housing, and everything. It's about $23 more than just the impeller, "It comes in a kit with the housing"

Answer 8

15hp Outboard

Answer 9

don't believe what that guy just said. that's wrong. always clockwise with the shaft on a standard rotation engine. you might pull the t-stat and check it. check compression, it could be the head stopped up. you're dealing with an almost 30 year build-up of "stuff".

Answer 10

your pluged up somewhere,if you ve checked everything below the power head (engine) and its ok,you need to pull the cyl head(no big deal unless you dont use new gaskets upon reassembly) and make sure the water jackets aint pluged,seen it before,expecialy if its been run in salt