This is part 4 in a series on fixing the water cooling system on my Johnson 6hp 1967 outboard (part 1, part 2, part 3).
So it was time to call in the big guns. Luckily Sam and his dad Lloyd have been working on outboards their whole lives (& then some) and had some time to help me out. As a recap, the initial water intake screen, the tube between the propeller and the impeller, and the impeller itself all seemed reasonably fine (but we replaced impeller in part 3 while in there anyways and kept the old one as a backup). In addition the final bit of tube for exhaust \ water outflow tube was fine. So the problem was in the middle of the system.
The first step was to grab some Muriatic Acid (watered down hydrochloric acid) from the local hardware store, in case we needed to run it through the water cooling tube (be careful, I wouldn’t use pressure myself). Lloyd said that, before resorting to acid, he’d try to get a little farther into the engine block (he seemed to be pointing at the Powerhead Group Crankcase area). But it’s good to have the supplies you need and it was only $6.50 at Home Hardware in Sidney:
Once we got to work the first step was to remove the old broken thermostat and gasket from the top right away. Not only was the spring broken off the top but the whole unit was encrusted with salt and corrosion:
Next we fired it up to try and get some water down through the tube in the engine block (and partly in the hope that those shoe elves had fixed it for me, but no such luck):
We did see the water drain in slowly and release a couple of slow air bubbles. A good sign! There’s a chance that the block started loosening when we got a bit of fresh water in there the weekend before to work away in the heat all week. It certainly didn’t hurt. To try and encourage the movement of water and air, we blocked the exhaust tube with a finger to create a bit of suction, but there were no miracles.
So we went out to get a new thermostat, gasket and seal at Sherwood Marine for $40 (I didn’t get a picture of the part numbers unfortunately):
I also grabbed some 2-stroke Johnson engine oil while we were at Sherwood Marine in Keating Cross Road. Leeroy Wisner suggested that other 2-strokes used on land (like weed-whackers) tend to run a little hotter than an outboard so the oil is a different grade. That sounded reasonable enough to me:
To replace the thermostat we first needed to plug up the holes for the water system, and then use a wire brush to clean off the ruined old seal (tip – if you can’t find a seal you can cut up old cereal boxes into the right shape and stack up 2 or 3 layers and maybe add some gasket goo if you like)
Lloyd made us solemnly swear to use grease, grease and more grease. He said his old man made him use lots of grease, and he’d seen years later that even if the bolt was almost gone/eaten away by salt water corosion the sections that remained would turn in the housing:
Once we got that new thermostat in and fired it up again, there was actually a tiny little trickle of water peeing out the exhaust hole already! By this point we’d added a good solid squeeze of dish detergent to the garbage pail of water to really start lubricating and loosening up the water cooling system. But there was still not enough water flow to say it was fixed.
There was still a blockage (slowly getting looser from fresh water) not far up from the bottom/impeller in that copper tube heading towards the engine block. Lloyd and Sam had a good trick with a stiff ~14 gauge chicken wire hammered flat on the end to make a shovel. With the motor sitting upright so bits would fall down with gravity Sam pushed the stiff wire up from the bottom and twisted a bit to clear the salt block. Then we poured in some more fresh water at the top and blew compressed air down through the engine block area, and blew the bits out the bottom!
Then we ran it again in that giant garbage can of water (to totally submerge the impeller housing and lower unit) mixed with a good squirt of dish detergent. At that point water was flowing out really nicely like in the YouTube videos and the engine block stayed cool!
Finally here’s a video of the Johnson Seahorse 6hp 1967 Outboard Cooling again!
What a great feeling that was. And here she is back onboard the Islander 21′
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