Mercury water pressure low

[Gecha (Gerry)]

Good luck Matt replacing your impeller. The kit is the best way to go, as you might need some other seal or gasket once you have the lower unit removed. It's a fairly easy job, just take your time, take pictures as you remove parts, and watch U tube videos if not sure.
Let us know how it went.

[fishmaster176]

Make sure you reference the serial # and model # when ordering your parts. As has been suggestec, get the complete kit with seals. Not a lot more money and is cheap insurance for trouble free runnning.

[Matt]

I found the kit I needed by using my serial on the Merc site. Found an original kit and ordered it. Nobody had it locally.

[fishfarmer]

In my experience it is easy to take the impeller/water pump, etc and replace what you can, but it can be a pain to put the lower unit back up. I have a 1985 35 HP Merc and both times that I have worked on the lower unit I have a hard time getting the upper shaft to lock back up into it's home in the shift assembly. I have actually pushed the shift arm out of it's seat several times. My lower unit is quite heavy and can be done alone but is much easier with two people.

I've had wasps completely fill the tube running all the way up to the engine compartment(this spring). My engine dribbled on the initial start after replacing the impeller, so I knew there was water getting through, but found mud all up in the tube and to a nipple which screws to the engine compartment. I tried cleaning that out, but suspect I have to remove the nipple to get the rest out, which is another project altogether.

[Matt]

I finally got around to replacing the impeller, seals, washers and plate. Only a little better though...from the videos I have seen of other mercs, the water should be shooting out, mines seems to be lacking....where should I start from here? Unhook the tubes and clean them? And yes the lower unit was a pain to slide back in....had to keep turning the spindle and keep trying to get it to slide in. Overall not too bad.

[Vtmopar]

What did the old impeller look like?
Pieces missing that could be plugging up suction or discharge?
Some motors just dont pump water well on muffs.
May need to use a plastic barrel or put the boat in water.

[Matt]

What did the old impeller look like?
Pieces missing that could be plugging up suction or discharge?
Some motors just dont pump water well on muffs.
May need to use a plastic barrel or put the boat in water.

It had grooves worn in the rubber. Probably from sand erosion?? Is it possible the motor has to be warm before the psi goes up? I did notice some sand inside the housing...should I unscrew the brass fitting in the cowling and let it run with muffs for a while on idle?

[Reelax]

I would lake test it at this point. You may see good flow in the water.... Is the flow better after the new impeller?

[Matt]

Better but not a huge difference. Ill try to lake test it this weekend.

[Crayfish]

Matt ... I've had weeds/mud clog up the "pee hole" in the side of the motor housing. I disconnected the hose from the back of the fitting inside the cowl and then took an air compressor and blew out the "pee hole" and the hose. Water flow went up a lot after that. Good luck.

[Matt]

The pee hole is clear for sure but maybe theres mud in the line itself or the brass fitting. That would be the first bottleneck inside the cowl that I could access.

[fishfarmer]

I'd check the line. I finally took off the nipple from my engine compartment. Mine is actually a plastic fitting. It was completely plugged with mud/insect parts. I put that and the hose back on and it pees like a champ now. Do that and what the others suggested about a barrel or lake run. Mine pees much better under full power in water.

[fishmaster176]

There was mention of hitting the "telltale" (peehole) with compressed air. Good idea. I had an issue with lack of flow when my 115 was a year old. I brought it to my dealer, VT Home and Marine, and Bob gave it a couple shots of air. He said it was plugged. Worked great since.

[C-Hawk]

Do not think that you wasted your time changing the impeller. This is an important routine maintainence procedure. I think that you are probably going to be alright, your motor must have a shut down mode or a horn in your console for overheating anyway. A Johnson I once had had a safety mode that limited rpm to 2000 when it sensed that anything was wrong, just to get you in. A good rule of thumb is, if you can put your hand on the power head while it is running, it is probably getting water, no mater how much is coming out.

[Matt]

Took the hoses off to find small pebbles trapped in there. Blew them out and have 10x the flow now!