CD12 strange cooling issue

[Fastwin18]

Hi All,

 

Just completed the restauration of my new to me CD-12. I’ve completely overhauled the gearcase, ignition, carb and  replaced the impeller, prop shaft seal, drive shaft seal, and the shift rod O-ring. It fired almost immediately, but it’s pumping just a tiny amount of water. It starts with a reasonable amount (but about half of what I’d expect) and then reduces to just a trickle after 5 or 10 seconds.
To isolate the problem I’ve removed the power head and put a drill on the drive shaft. Water then shoots out a couple of inches above the top of the draft shaft.
So I figured the problem must be in the power head. I removed the side/exhaust cover and surely enough one of the bolts broke. Apart from that everything looked as clean as a whistle. Just to be sure I blew some pressurized air trough all the openings to check for blockage, all seemed good. So I closed it up again and ran it in a barrel. Problem not solved.
Then I removed the cylinderhead, just to make sure all the passages were clean. They were.
Any ideas as to what else could be causing this problem or where to look?

[crosbyman]

did you install the proper base gasket# under the PH ??

see   pattern differences …

Johnson Evinrude outboard impellers, seals, lower unit kits, water pump kits, gaskets – VintageOutboard.com

 

 

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Fastwin18

[Fastwin18]

Thank you Crosbyman.
I’ve reused the existing base gasket but ordered a new one at vintage outboard.
The current one needs replacement but seems to be original and correct.
I’ll pull and inspect the pump housing later today and let you know how that worked out

[crosbyman]

check pump impeller key !

 

btw  if you need the Cd12 parts listing I can send via email  …file is 3meg +

 

send me  PM  with Email

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[Fastwin18]

I’ll also check the key but I’m fairly confident that it is OK. Thanks also for the offer for the parts manual but I’ve already downloaded it from the forum. Probably posted by you 😁

[Fastwin18]

Back to the shop….

[Fastwin18]

Crosbyman,
In order to eliminate the base gasket, would it do to remove it temporarily and check the waterflow?
Or will that actually prevent the water from flowing down the proper channels?

[Fastwin18]

I don’t think it’s the water pump or lower unit

[crosbyman]

I would not operate without the base gasket as long as it is the correct one it should not be the problem you seek.

water could seep out and into a place it will cause worse problems!

if water does not come in properly……….. it is restricted going out and there is no thermostat   anyway.

remove  the  rear  exhaust cover 303585   to inspect the outflow of water  or try  a backwash to clear water passages.

did you pull cyl head and inspect  jackets ??

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[Fastwin18]

Well, what I thought was an original base gasket seems to be a custom made one. Which would make sense because these are impossible to get over here. Don’t know how I’ve missed that, usually these gaskets are black, not creme.
One of the holes was blocked, the one I’m pointing at with my finger. I’ve opened it up thinking I had found it. But it made no difference at all. Yes I’m running the engine without the rear exhaust cover so I have a visual on the water flow.
I’ve also checked all the water passages in the cylinder head. No debris or pieces of impeller on there.
My main suspect at this moment still is the base gasket, although water can flow freely from what I can see.

[Author]

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