Old Merc has trouble peeing water

Hey guys just changed out the water pump impeller, housing and gaskets on lower unit with the hopes that the motor would cool. When I got the boat the old guy told me that the water doesnt pump unless your on the throttle. Now it pumps on idle but only drips. And as far as being in the throttle its pumping but its not a straight strong stream and its actually steaming and is way to hot to touch. Any help will be greatly appreciated. Im only using the hose clamper on the bottom of the motor. Do you think it would be better if i launched the boat?

Re: Old Merc has trouble peeing water

If it is too hot at idle putting it in the water won't help.
You didn't specify which engine.
Could be corrosion in the adapter plate under the powerhead allowing the incoming water and exhaust to mix, blockage in the water jacket(s), or a leak in the exhaust.

Re: Old Merc has trouble peeing water

You may have done the same thing I did last year, not seated the water pump lower housing properly. Mine had the same symptoms as yours but only
when running in the upper rpms. It took me a while to figure out, It will help
if you have a depth mic or calpiers. I ended up having to use a dead blow hammer to get the lower water pump housing seated all the way.

Re: Old Merc has trouble peeing water

Sounds crazy but my 115 had the same problem and all I did was blow some compressed air back threw the pee hole never had a problem since easy thing try I assume I had a clog of some sort but it cleared it up.

Re: Old Merc has trouble peeing water

Are there any thermostats? Might need some new ones.

Re: Old Merc has trouble peeing water

My first thought is possible blockage as already mentioned...

Re: Old Merc has trouble peeing water

I have a much smaller motor, but when i changed the impellor i had to make sure that all the legs (for lack of a better word/knowledge) of the impellor were curved in the same direction, example: if the shaft spins clockwise all the legs of the impellor have to curve to the left when inside the housing. I used some quicksilver multi-purpose marine lube, applied some to the impellor and had a buddy spin the shaft in the proper direction and while installing the housing insured that the legs were bent in the proper direction using a small screwdriver. I was also wondering if it has a thermostat but i see that it was already mentioned. I have also found that them mud dabber wasp had made a nest in the pee hole hose. Blowing air inside the hose to clear it only puts the thing that clooged it back inside your motor i would think there would be a chance that that could just clog it up again.

Re: Old Merc has trouble peeing water

thanks for all rhe responses!!!!! I started on it sun morning and quit at sun down trouble shooting it. i blew my compressor in the hole and even took the 90 off the block where the pee hose comes off the motor. i could feel rather hear the air coming from below the the bottom fin. it didnt pump anything until we trimmed the motor up and filled the water passeages with water. at frirst it only blew out steam then it spit some quirts out then i put the littlecjhoke lever up into a higher rpm and then it pumped. but like i said it was a stream and iwas glad to see it but it was boiling off before it hit the ground. Its an old 1974 merc 850 thunderbolt. So its not blocked, i sort of pumps, cranks right up so its not a head gasket, i dont know so hopefully you do Tim at tims marine in Miss. said he woould look at it but i would like to pinpoint the prob before i dump all this money into an unreliable motor ya know. thaks guys

Re: Old Merc has trouble peeing water

Those motors do not have a thermostat. They also should run dead cold at idle. Are you using a flush device over the water intakes, and using sufficient water pressure to force the water up into the waterpump? if the waterpump is run w/o water, the rubber will melt or worse, and you will need to replace it.

You did install the water hose into the waterpump cover, when you replaced the impeller?

You might drop the lower unit and put a hose w/ low water pressure on the water intake hose and see if you have good flow across the waterjacket on the head and exhaust cover.