Re: OMC Saildrive 15 hp
When the shop told you it was 15hp they meant the saildrive model is rated @ 15hp. The 15hp Zephyr Saildrive is rated at 15hp but the power-head used is also used for OMC, Johnson and Evinrude 20-35hp outboard engines but it has been de-tuned to 15hp in the case of the saildrive to extend longevity.
I have 3 of these units and have used one of them for over ten years. They do indeed have impellers over the main shaft between the upper and intermediate cases. There is no external water-pump. The raw coolant water enters at the skeg forward of the prop and is pushed through the engine and out the exhaust riser by a rubber impeller.
If the shop actually meant the "powerhead" is from a 15hp engine, they are wrong. All OMC Saildrives used the same generic 20-35hp OMC powerhead.
If the engine is heating up it's either a plugged entry port, a worn out impeller or possibly a faulty thermostat. Other than noise and occasional stink, my engine is reliable, trouble-free and powerful.
1981 Aloha 8.2