To start or not to start, this is my question.

Jacko40 hp

Dec 3, 2019
Hi everyone, so first time ever using a forum bit I’ve gathered useful information from them over the years. I’ve always been told and repeated if you don’t know ask and no question is a dumb question when you are asking for help.
I own a 2006 Honda 40hp Honda and it went in the saltwater, it never got fully submerged but enough to get water in the bottom pot. At the time the engine wasn’t running and it was in the water for about 10 minutes max before we got it above the water. The boat was immediately towed to shore, washed down with fresh water and the sparks plugs removed to drain the water while it was turned over by hand. When I got it home the oil was drained and oil filter replaced. I’m on a budget so I haven’t pulled to head off as I can’t afford to get the kit to rebuild it. With it all cleaned down and fully flushed, new oil etc she will wind over freely by hand. All electrics are ok and working perfectly. My concern is I haven’t been game enough to start it cause I’m afraid she might blow up. When looking into the spark plug ports I can see a rusty colour and am concerned the salt water has done damage and once she fires the end is nigh. I know i should be pulling the head and giving it a good once over but cash is the issue. Do you think it’s worth giving it a start or will I just do more damage.



Supreme Mariner
Dec 28, 2013
Motors MUST be running soon after a dunking.----So start it up !!------Run for 10 minutes and change the oil again.


Sep 16, 2013
Another vote for running ASAP.

I always prefer to run these in a trash can or barrel as when run on muffs, there is a water intake right above the prop that will be sucking air. That means nothing above an idle, NO EXCEPTIONS unless you put a piece of tape over that hole and manage to keep it there.

Run it long enough to get it good and warm. Remove the oil filler cap and look for water droplets or milky white deposits. That's a sign of water in the oil.

If you see that, you can change the oil again, and run it again - just make sure you run it long enough to warm up the oil, to sort of boil the water out of it.

These things are pretty well known for their ability to mix water with the oil, even without submerging them in salt water. It's usually a bad head gasket, but it can easily be a holes corroded through one of several areas of the block as well. I work on these quite a bit and see the worst, so I've pretty much been there done that. A lot of work to change them, but you can buy short blocks (comes with pistons and crank assembled in a block) on ebay WAY cheaper than you can replace the motor.


Supreme Mariner
Jul 18, 2011
+1 on starting it up. . . . that's a general rule when our OB goes swimming.

Lou C

Nov 10, 2002
If you are worried about rust in the cyls….try this....
disable the igntion system and remove the plugs, spray PB blaster in the cyls and let it sit a few hrs, Then follow that with fogging oil like we use for winter storage. Then spin it over with the starter, this just dissolves any rust present and lubes the cyls before starting it. Then replace the plugs and start it up, expect it to smoke a bit, it might foul plugs but you want to burn any moisture that is in the oil OUT, before winter storage. If you can give it a good run on the water, so much the better but change the oil till it does not show any sign of moisture, it takes approx 120-150* oil temp to burn off the moisture, just running at idle may not do it.

I saved a GM marine 4.3 this way that had both head gaskets blown, I had water in a cyl, what I did was remove the plugs, drain the block, cranked it to blow out the water and fogged cyls. This was after changing the oil and filter 3 times. When I took it apart, I still had some milky oil in the cam valley but the cyl heads and cyls were clean and free of rust. And this was salt water. When I took it apart, I found both HGs blown. I took the cyl heads to the machine shop and they recommended replacement based on the fact that they had cracks in the center cyls (prob from the overhead that weakened the HGs) and the water passages were eroded from 15+ yeas of salt water use. I put it back together with re-man cyl heads and new gaskets and its been fine for 2 years.

Using PB blaster or Kroil to dissolve the rust, followed by fogging oil to lube the cyls, seemed to have helped. When I took off the heads there was no rust on the cyl walls at all.


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