CD12 strange cooling issue

[crosbyman]

see post 297605     🙂

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[Fastwin18]

Thank you all for your very helpful suggestions. I didn’t have time today but I’ll report back with my findings as soon as I’ve had the opportunity to look at it

[bob-d]

As Fleetwin said, look at the actual motor castings under the gearcase impeller plate. I had a motor  where water didn’t flow out properly for the winter and it cracked the gearcase castings under the plate, causing cavitation.
It drove the group crazy trying to figure out what was going on. Frank the guru, finally came up with the solution. Changed the gearcase and all was fine.
if you could shoot a picture of that area, I think it would allow us all to look and rule that theory out.

Bob D

[Mumbles]

Fastwin18 says:

‘reduces to just a trickle after 5 or 10 seconds’

Well, that little morsel  of information tells me quite a bit. Mainly that the water pump is working fine but something is causing the flow to drop off.  When this happens, it’s usually caused by something with higher pressure than the pump can develop, something like exhaust gases getting into the cooling system.

Was the motor run in a bucket with the gears engaged? If so, the prop can churn up the water allowing air or exhaust into the cooling water. Try running it in neutral or with the prop removed to see if it makes any difference.

Exhaust gases can also get into the cooling system thru the water pump or thru a leaky head gasket.  The pump housing has two small holes in it and the one in the middle is an air bleed while the one right below the water tube grommet bleeds water into the central finned area to create a reservoir which prevents exhaust gases from being sucked into the pump. The fins help to keep the water from sloshing out. It might be worthwhile to make sure this hole is clear as they do tend to get plugged.

A leaking head gasket might not be so obvious but any sign of moisture or rust on the spark plugs could be an indication.

4 users thanked author for this post.

David Bartlett, seakaye12, Fastwin18, aquasonic

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