Dumb question here..... not to hijack the thread, but what is a knock sensor?

It allows the ECM to advance the timing as far as possible until microscopic pinging start, then it retards it just enough to stay at that critical, most efficient point.

Thanks D!

Here more info on how the actual sensor works: http://en.wikipedia.org/wiki/Piezoelectric_sensor

And that fitting makes it a little harder to drain the water from the block, as the wire you poke in there might need to have a curve in order to get the trapped sediment out. Glad I only have one on my Mercruiser.
FC, I worry about that brass plug. Hope it comes out easy, or you are gonna unsrew that whole fitting when you go to drain the block. That is one area where Mercruisers little blue or black plastic wing nuts are very handy to have.

Knock sensor makes sense. Thanks guys. I'll be spending some time today poking around my engine and figuring it all out, it sure is different than my carbed 4.3 V6 I had on my Sea Ray. And this one really is down in there, talk about a PITA to reach anything!

I miss those little blue plastic wing nuts I had on my Mercruiser. This one will be a PITA for sure. The knock sensor/drain on the starboard side can't be seen. I will have to feel around to find it.

Weird place for a knock sensor, but that's what it is! They DO also put a temp sensor in the same place, but it's much different looking. From Marine Parts Plus website, edited for better detail:

Brass plug came right out. Just tried it to be sure. This motor won't be hard to winterize at all. Do I need to coat the brass plug with antiseaze or loctite so it won't stick?

I would not recommend any kind of anti-seaze or loctite for a brass fitting or plug.

I always wrap some Teflon tape around the threads of any plug or fitting that threads into the water jacket of the block or manifolds as protection against leaks.

Thanks Admin. I did not think of teflon tape. I should have though, I have a 10 pack in the garage!

I'd buy one of those blue Mercruiser plugs!

The merc plugs are nice until you overtighten them or they stick in there and you break the wingnuts off. Then you have to get in there w/ a screwdriver or something of the sort and hope you can back it back out. But other then that I like them.

Part #? I haven't had any issue with them breaking off on my last boat.

FC, when they break, they lose all clamping/holding force, so removing them with your finger tip is possible. Ask me how I know! But if a screw driver is available, it makes it very very very easy to remove them, when they break.

I believe it. I take it they should thread right in? Have an idea on cost or a part #?