steam thru prop hub merc 260?

[Marshall1]

I am working on resolving an excessive steam issue with a Merc 250 (350 ci).
Excessive steam is coming from the exhaust. I noticed that steam is also coming from the center of the propeller. Is this a normal route for exhaust to pass?

[marshmat]

There are several possible exhaust configurations. Which sterndrive do you have- Alpha, Bravo 1, etc? Most Merc sterndrives can be configured for through-prop exhaust, through-transom exhaust, or with the addition of an exhaust diverter, switchable between the two. In the case of a through-transom exhaust, some are wet (cooling water is sprayed directly into the exhaust pipe downstream of the manifold) while some are dry (the exhaust is either not cooled or the cooling water exits separately). It would help to know what setup you have.

[Marshall1]

Matt,
Thanks for the reply. The "standard" configuration is wet. Exhaust from the MR260 (350 engine) is mixed with water in the manifold/risers and exits through two 1"+ holes in the stern drive at the transom. [I also have a diverter that can switch the exhaust to the sides of the boat. But I dont believe this is a factor.]
I am getting excessive steam throught these holes and throuogh the prop hub. I would also like to add that very little if any water comes from the propm hub, just steam which leads me to my question.

My biggest concern is the excessive steam, secondary question is why steam is coming form the prop hub.

as a test, I connected a garden hose to the lower unit to pump outside the boat. I connected another garden hose prior to the oil cooler. I know I am getting pleanty of water to the engine.

[Zackman]

A little bit of steam may be normal, espcially on a humid day. Excessive amounts, with out high engine temperature, would suggest that the exhaust is too hot and flashing the water into vapor (sorry, could resist, since technically you can't see steam).

It sounds like there is a restriction in the cooling side of your exhaust. The risers should feel only warm to the touch and you should be able to keep your hands on them without any discomfort. You may need to pull the exhaust manifolds and risers off to determine the extent of the blockage.