78 Mercury 7.5 horse

[SeaNymph14]

Bought this motor from original owner, excellent condition. However the cooling stream of water coming out the side of the motor got progressively weaker, and finally quit altogether the first time out on the water. I limped it home. Not being familiar with outboard mechanics I assume the coolant pump is out?? Any advice?? I am told parts for this model may be difficult to find. The marinas in the area say they don't work on them this old.
Thanks

 

[DVL]

Re: 78 Mercury 7.5 horse

The first thing I would check is the impeller. If that is good it may be your thermostat. my bet is its your thermostat as when my impeller goes out on my 72 7.5 you go from good stream at the tell tail to no stream right now.

 

[jbjennings]

Re: 78 Mercury 7.5 horse

Yes, I agree with the impeller. You should never "limp" home, though. When the water pump quits, you're better off killing the motor else risking burning it up. You can find all the parts you need for the motor. You can order them here at iboats even. If you need a diagram to help you find parts for it that includes part numbers that you can use here on iboats, then try crowleymarine.com and you can find parts diagrams. Go to parts cagalog and then put in mercury, year, hp, etc. and it will show you a diagram. If you are missing some of the blades off the impeller when you drop the lower unit, try to find them all, otherwise they could be in your water jackets stopping up the water flow throught the engine. If you do it yourself, don't lose the impeller key from the driveshaft when you pull out the old impeller. there's a ton of old threads on this if you search this forum. I know 'cause I posted quite a few myself.
Good luck,
JBJ