I/O- water backing into the engine from the exhaust?

[jimski2]

If you buy an older I/O, water can back into the engine through the exhaust if you hang a kicker motor on the bracket, a cooler of fish on the transom, downriggers and a couple lard bodies on the lines. When the kicker is running the water will come into your main engine exhaust manifold and with no exhaust to blow it out it will flow in your cylinders through an open exhaust valve. When you go to start the main engine, it will turn a couple degrees and seize up since you can't compress a liquid in the cylinder. Your starter may blow, flywheel teeth will break, bend a rod or worse. The newer boats have overcome this secret fault by having wider transoms, but the older guys have this design defect. Be careful if you hang a kicker motor on a swingdown bracket on an older I/O.

[InTheBox]

jimski2,

When you say older I/O. Do you mean 1990's and lower?

Pat

[FREEMAN77]

I just bought a 1981 20' sea ray with a 305 merc I/O should I worry about this? This boat is my first I/O so any other info anyone has that Ishould know let me know.

[borderline 350]

Dear FM 77, Your 81 Searay should be a Mercruiser I drive. At idle you will hear a click/clack...click/clack from each exhaust riser. This sound is the anti-reversion flapper valves (located just below each riser) .If they are working properly (and not damaged from overheating,age, etc.) water entry will not be a problem UNLESS you overload the back of the boat!! Open the engine hatch and be sure you can hear the flappers working! If jammed partially open or damaged, YOU WILL NOT HEAR them! If you are trolling down wind in large following seas, you can also take water up the exhaust WHILE IDLING!. You can take water up the exhaust and into the engine by backing hard in reverse and stalling the engine while at fast idle! Such as a panic reverse when docking.

Fortunately most of the better boat mfg's (SeaRay)install the engine at the correct height to minimize water entry into the exhaust. But I have started to see corroded exhaust risers on these early 80 boats that have seen high hours OR BEEN IN SALT WATER! The source of water entry thru the exhaust has been a major problem for many years and can usually be traced back to overloaded sterns and operator error. Just another problem to add to the long list of "Boating Fun"!!

P.S. Thats why you see the go fast boats with exhausts above the swim platform. Long duration race camshafts will allow water to enter at idle due to the pulsations present from the increased valve overlap.

Don't worry about this unless you see hard starting and engine skips at idle. Then be concerned. HYDROSTATIC lock can bend rods and break cylinder walls, been there, done that. Go fishing and enjoy!......Jet Boat Bill

[FREEMAN77]

well the boat I just bought had it motor all redone 2 years ago then was put away and it has not seen the water since then it seems to start right up and have no probs I will have it in the water in a few days if all goes as I want it to :roll: I will be sure tocheck for all you have told me to thanx

[LongLine]

If you suspect you're getting water in the engine, I'd suggest you check your oil dipstick frequently. Oil & water that have been stirred up will turn a creamy color. (Years back, I had a '66 mecruiser that developed a hole in the plate that separated the water jacket from the exhaust in the exhaust manifold. Sucked some water in every time I shut it down - drove me nuts finding it... but that's another story)

Tom B.

(LongLine)