'63 Johnson 5.5hp Overheating after Impeller Change

[Buzzwindrip]

I have a 1963 CD-20C that the seller of a boat I bought gave me as a non-working motor. I finally got around to replacing the impeller, and got it back together today. Put it in a tank, and it ran like a top once I got the mixture right. As it was running, I noticed that the power head was getting to be hot enough to sizzle spit, so I shut it down. What I noticed as it was running:
There was more mist than slurry exiting that port on the exhaust housing. Every now and then, there would be a larger volume of water that would spit out, but it wasn't consistent. When I pulled the T-stat cover, it was bone dry in the cavity. When I started the motor with the T-stat cover off and T-stat out, there was no water entering the T-stat cavity. The only water entering was some occasional spray/steam from the outlet side of the T-stat. I poured water into t-stat cavity, and it did drain from there slowly. Tried the same thing while the motor was running, with the same result. Blowing air into the water inlets while the power head was off showed no signs of blockage. The OEM pump housing did show wear and some pitting, but I decided to reuse it after getting some feedback here. Before I start tearing the powerhead apart, looking for anomalies, would I be able to spin the driveshaft with a power drill and check for pumping efficiency? Any ideas greatly appreciated.

 

[a70eliminator]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

I had just replaced the impeller on my 5.5 last year and had to pull it all back apart to remove little bits of the old shreded impeller that had the water passage blocked.
Also I'll mention you have that motor sitting in a deep enough tank for the impeller to be below the waterline, it wont suck water up.

 

[1946Zephyr]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

Yes, exactly. Pull the lower unit back off and turn the shaft (clockwise only) and see if it pumps water. If it does, then you may have a clog in the water tube somewhere. They usually like to clog where the tube goes into the motor leg, but you can test that, by attaching and air nozzle to it and see if air blows through, out the thermostat cavity.

I just rebuilt a lower unit, on a 62 Evinrude 5.5, so I'll have my fingers crossed too.

 

[Buzzwindrip]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

I definitely had enough water; well over the anti-cavitation plate. What bugs me is that I blew air into every orifice that had to do with the cooling system: on the bottom of the powerhead, in the motor leg, and even the intake areas. Not any blockages. I will do it again with the T-stat cover off, and then pour some water down there to see if the slow drain is the cause of my problem. I will report back with my findings. Thanks for the feedback!

 

[jbjennings]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

the anti-cavitation plate has nothing to do with anything as far as the water pump is concerned. The pump is not self-priming. The water level needs to be above the bulge in the top of the lower unit where the water pump is. I like the water level to be about 3 or 4 inches below the exhaust relief.
The water level could easily be your problem.
JMO,
JBJ

 

[F_R]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

the anti-cavitation plate has nothing to do with anything as far as the water pump is concerned. The pump is not self-priming. The water level needs to be above the bulge in the top of the lower unit where the water pump is. I like the water level to be about 3 or 4 inches below the exhaust relief.
The water level could easily be your problem.
JMO,
JBJ

I agree 100% with what JB just said. Especially since the pump housing is worn. Exhaust is blowing down into the pump through the drive shaft hole because the impeller isn't sealing on the sides. Remember, there is no water in the exhaust housing where the pump is when it is running because the exhaust blows it out. For that reason, it may work just fine when turning it with a drill, because there is no exhaust. But put the powerhead back on and back to the same old problem. The pump housing may have to be replaced---or at least should be replaced.

The aluminum pump housing is obsolete. Unless you can find one, you have to replace the whole water pump kit with the updated plastic one with stainless steel liners. It is a totally different pump, but fits and works fine. New pump kit is part number 763758, about $50.

 

[Buzzwindrip]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

Thanks for the info. I was definitely ok on the water lever; nearly up to the exhaust relief port on the exhaust housing. I just assumed the water pump was submerged when running; it's good to know what is actually going on in there. I am just going to order the pump upgrade, and go from there.

 

[Buzzwindrip]

Re: '63 Johnson 5.5hp Overheating after Impeller Change

Just an update, mainly for those newbies like me that search these threads for answers. I finally got around to pulling the power head after having this cooling issue, and decided to look down the exhaust housing with a pen light before pulling the lower leg off. Doh! The water tube wasn't even stuck into the top of the water pump. I pulled the LU, lightly greased the tip of the water tube, and reinstalled the LU. This time I was sure the tube was connected, and realized that while jostling the works trying to get the shift shaft into shift-lever arm, I must have pulled the LU back enough to disconnect the water tube the last time. I got into a water tank today, and it cools perfectly, with a nice strong slurry of water coming out the blowhole in the leg. I still have some tweaking to do to get it running right at very slow speeds, and found some water in my LU when I changed gear lube again. I had also found a water leak coming from one of the screws on the cover that is on the tiller side, just around the corner from the cylinder head. That was easily cured with some re-tightening of the all the screws on that plate. Now that the motor appears to be a keeper, I guess it is time to get a manual. Hope this helps someone in the future, and thanks to all that offered help in the past.