Re: 15hp exhaust & water leak…why?

[Don]

I am confused also because you are reporting test tank cooling issues that are opposite from the normal woes. Engines usually cool OK at lower speeds in the test tank, cooling gets messed up at higher speeds in test tanks due to aerated water. At this point, I wouldn’t worry about the cooling if everything is OK while running on the boat. In actuality, the early 9.9/15s had fewer cooling woes than the later models, there were no grommet issues on these early engines (unless/until someone replaced the original style grommet with the flawed newer design). The only thing I remember happening was with the original aluminum/SS impeller housings. The salt water would work its way between the aluminum and SS and actually crush the SS liner inwards which usually led to impeller damage/spun hubs and loss of cooling. Needless to say, this problem is solved when the water pump is serviced and the newer plastic/SS housing is used. These engine don’t have a cooling telltale which can lead to confusion though. There is very little cooling water escape from the upper exhaust/cooling relief hole when you first start the engine. You will see a fine spray as the level of water rises inside the exhaust housing or when the thermostat opens.
Jeez, these old beasts are seeking you out! The latest 74 model that found you may just have a partially plugged/dirty high speed jet causing it to falter/die out at higher speeds. Please don’t assume the worst and rip into the ignition until you have run the engine and confirmed there is an actual ignition fault. What spark plugs are you using in these engines? I believe the latest champions are the UL-81J, or UL81C. Some guys report better performance/plug life with NGK plugs, but I don’t know the number/style they use.