Merc 4.5 cooling problems

[jolson123]

I have a 1980 Mercury 4.5 that wasn't pissing. So, I replaced the impeller. It spit few times, and then it turned to steam. I thought part of the old impeller might have got stuck, or something.(nothing) So, I tried air & it's bypassing the tube up near the head. So, I took the main shaft housing off to see what I could see. Not much! I don't have a manual, and know nothing about these?

I don't know if it's a blown gasket, or something of that sort. Is there a sort of suction created above the impeller?

Thank you & any help would be appreciated! (Info, diagrams)

 

[Downwindtracker2]

Re: Merc 4.5 cooling problems

When I changed my impeller on my '81 4.5,I put the plate that came with the kit on. That was my mistake,it isn't needed on that motor. There is no suction on the top. I ended up having the bottom pulled off half a dozen times. I don't know if that helps you.

I have the factory and the Seloc manuals,the Seloc is good enough.

 

[Laddies]

Re: Merc 4.5 cooling problems

I don't make a habit out of correcting poor advice but you certianly got some from Dwt II. All US built single cyl engines like yours use a impeller plate, that means all. Then maybe that's whats so good about a Seloc manual.
Your engine is probably plugged with impeller pieces, first drop the lower unit and hook a electric drill to the drive shaft put it in a container of water and run it with the drill to check the pump USE CARE as the prop may turn. It is common for the 2 grommets on the pump pickup tube to leak and suck exhaust, so they may need sealing. The other problem impeller bits may have plugged the intake passage to the pump or even worst the engine cooling passages, that requires the power head to removed from the mid section and the plastic grommet on top of the supply tube checked (they will melt and restrict water flow) Then remove the exhaust plates and water jacket cover and do a careful check for pieces. They commonly are between the exhaust plates but with the power head of check the cooling passages from the exhaust cooling to the waterjacket.

Poor advice is no help to anyone.

 

[Downwindtracker2]

Re: Merc 4.5 cooling problems

Your're right.I guess the word plate was wrong,I certainly didn't mean the outlet port plate,rather a thing that looked like a washer. And it came with the impeller.I put it in ,figuiring the last guy had left it out. Only when I took it out, did I get water out the telltale. Confusion doesn't help.