Re: 1978 evinrude 115 HP pees steam
do you have muffs? if so muffs may provide enough water pressure to push water through impeller and block to see if it does this again at home.
Safe bets in my opinion, replace the impeller cheap insurance, note the condition of it when you replace it, if your missing pieces or entire fins...you have to ask yourself where did they go (could be causing blockage in the powerhead).
since you will be waiting on impeller to get to you, may as well replace or at least check thermostats... my two cents, if you checking em...replace em they are far cheaper than a new powerhead.
While your at it... check compression on all cylinders, please post the numbers... it is possible but less likely that you could have popped a head gasket or cracked something between exhaust and water jacket.
check the screen on lower unit... was there weeds, plastic bag....goop ect... stuck in the inlet.when you have lower unit off... you will have clear access to the water tube that goes from the water pump to the powerhead... you may wish to put some low pressure air through it to make sure it is clear and not plugged... you may also wish to send a bit of water via hose up it to see where it comes out. I know on my 1983 15hp (yeah i know 100hp less) the grommet that the water tube goes into at the powerhead was swollen and needed to be replaced as it occluded the water flow. also there were bugs galore in the water line and it was pinholed pretty badly. I believe this was the cause of the head gasket failure that brought it into my possession for next to nothing.
As far as the impeller disconnecting from the hub... maybe, but i would think less likely... regardless when you replace it you can inspect it ... also check the volute case of the water pump and consider a new one if it is scored badly.
and lastly.... if someone else chimes in they likely know more than me so follow their advice.
Sean
yes they sell parts here too as well as being a great place to get advice. yours will look similar but perhaps not identical... and will be under the head, or in the head under a cover depending on your model.