I/O Characteristics

[Scott06]

Why not on a used motor?

There is enough scale rust and crud in a used raw water cooled engine such that if you add a closed cooling system with a heat exchanger you will repeatedly plug the tubes in the heat exchanger and it won't cool. So basic rule of thumb is once a raw water cooled engine always a raw water cooled engine

 

[Lou C]

You can remove the thermostat housing and the front circulating pump and look inside the intake manifold and the block, you can't see much but it will give you an idea how much corrosion there is inside. If all you saw was light surface corrosion that's one thing but flaking rust, will continue to flake, and will cause chronic cooling problems.

 

[mr 88]

Probably 95% of Starcrafts are sold in the Great Lakes , fresh water ,no reason for a closed cooling system . Yes they may run a smidgeon better with a closed system and your thermostat will keep it in right temperature zone. It was not cost effective for StarCraft to sell them with a closed system , may have been a add on . Parts for a GM straight 6 are readily available and they are great running engines , 100% better than a 4 banger. Outdrive is dated , the beauty is they are on Craigslist all the time for a couple hundred bucks. Heck I have 3 in my garage and do not own a I/O if that tells you something. Just have to make sure the gear ratio is the same . I believe the lower gears are all the same, they switch the ratio on the upper gears in case you run into something that needs some customizing. Most Sterndrive engines are in a doghouse , which allows you all the room in the world to change oil and filter without being Houdini , suck it out with appropriate tool and use a couple zip lock bags or a large Folgers Coffee Plastic container to do oil filter . No need for a remote in your case. Run it until it breaks , which may be after a week or after a few years . Don't lose any sleep over it , they are all a crap shoot .

 

[JimS123]

Not much love for I/O's here, but I still prefer them! I've owned various outboards, including a new EFI 4 stroke, and still like I/O's. Maintenance isn't that bad, it takes me all of 3 minutes to pull the plugs. Changing the oil is really easy, remote drain just pulls out of the bilge drain.

And the u-joints are more forgiving than people are implying. I've owned I/O's for 10 years now, and have to deal with shallow water. I frequently idle in/out of my parking spot with the drive tilted way up, I just make sure the prop and water intake stays in the water, usually. Total u-joints, gimbal bearings, and bellows I've replaced in 10 years? Zero. (and I'm not dealing with new boats here, my current is 20 years old)

The best part of an I/O? Price out repowering a 4 stroke outboard, but make sure you are sitting down. I can repower my I/O with a day of work and $2400 for a freshly built reman, or even far cheaper for a junkyard pull.

Don't listen to the "experts", read the freekin owner's manual.

Mercruiser says you can run an I/O up past the trim section as long as you keep the rpm below 1000.

Our sandbar requires us to go several hundred yards in shallow water. Eons ago, with the boat on the trailer, I raised the lower unit until the prop and skeg were just below the bottom of the boat. No chance for a collision. Noted the position on the trim gauge. That's how I traveled in the shallows. AFTER 35 YEARS, the OD was still perfect, after only replacing bellows. U-joint was like new. Of course I greased it as required.

All that said, after 35 years I just got sick of an I/O and bought a new boat with a 4-stroke OB. Boy that sucker looks cool hanging out there. 10% lower fuel usage, almost no maintenance, no winterizing and with the same size boat and the same HP she goes 5 mph faster....

 

[Scott06]

Don't listen to the "experts", read the freekin owner's manual.

Mercruiser says you can run an I/O up past the trim section as long as you keep the rpm below 1000.

agreed keep our boat in a shallow cove -26” deep at lift, every time i go out i have to have it trimmed almost to the point of the prop not having enough water to bite… in 50 years three boats between my grandfather, parents, and i changed one set of ujoints, keep it below 1 k and youre fine

 

[Lou C]

Yep the most I had to raise mine is 1/2 way up just run at idle in the shallows I have never had to change the ujoints in this boat…they are original….

 

[Scott Danforth]

Why not on a used motor?

Because you cant clean the shell side of a heat exchanger, so once the rust flakes indicated prior plug your new $2000-$3000 heat exchanger, you get to throw it away

 

[nola mike]

Because you cant clean the shell side of a heat exchanger, so once the rust flakes indicated prior plug your new $2000-$3000 heat exchanger, you get to throw it away

Seems like someone should make an upstream filter.

 

[KJM]

Seems like someone should make an upstream filter.

I always wondered why they don't make internal anodes on these engines and mannifolds like they do on outboards

 

[Scott Danforth]

Seems like someone should make an upstream filter.

then the upstream filter plugs 2.5 miles out on your first launch and you overheat. BTDT own the teeshirt and I know better.

 

[Scott Danforth]

I always wondered why they don't make internal anodes on these engines and mannifolds like they do on outboards

because the average I/O is bought and sold within the warranty period. no incentive to add extra cost.

if in salt water, block will last about 25 years, manifolds and elbow about 7-10

if in fresh water, block and manifolds will last until the hull rots or owner sinks the boat.

 

[Lou C]

The problem with a filter for the cooling system is that once the block/heads have flaking rust it will never stop, it's more or less constant. So any filter will get clogged sooner or later.

 

[Bob Sander]

Thank you all for the input on this. Only reason I am considering an I/O is because I am really wanting a very particular boat (25' Starcraft Chieftain) that is almost always equiped with the original I/O Merc 165. Funds always being a limiting concern, I am only able to afford so much at a time, and what I can fix myself, and was thinking I would get the boat model I really want even if it had the infamous I/O and try to get a season or two out of it before taking on the offshore bracket conversion that I would probably end up with in the long run. It seems sometimes boats are sold cheaper just bc of the unpopular old I/O setup. I'm a pretty good mechanic and fabricator so was thinking if the I/O is in decent shape I'd be able to keep her running for a time. I never leave shore without my trusty Johnson 15hp kicker attached. The remote mount oil filter sounds like a really good idea as I've heard that's a common pain. The Chieftains seem to have a very accessible motor setup luckily with a simple old carb, points ignition, and large motor cover that tilts away providing good access. Sounds like when I go shallow I would be best off running the kicker which wouldn't be that bad, especially if I linked it to the helm steering with one of those connector links. I don't cruise in shallows much, I just commonly visit uninhabited islands and nose up to sandbars and such. Too bad the Chieftain 25's didn't come with outboard setups from the factory! The sun pad thing is also a major attraction for the gf so that was another factor influencing the possible future I/O. I built a deck around the outboard on my current boat to try to make that rear sun pad area happen but I like the look of the closed stern area without a splash well being needed. Lot to consider apparently but glad to hear you can indeed run it tilted at idle or so to approach a shore in the shallows.

Ujoints aren't as bad as people make them out to be. I have straight U joints on the front axle of my jeep which bend at all kinds of crazy angles every time you turn the wheel. You just have to understand how they operate. They produce a "lobing" feeling when operated during a flex because the driven axle is being sped up and slowed down with each 1/2 revolution. Of course if you have a quality joint (which is not on my jeep!) they double up on the joints to cancel out that lobe effect.

While it's best to operate a U joint as straight as possible and they least complain that way, they are built to transfer power during a flex.
Good video on how they work. If you watch careully enough you can actually see the driven shaft speed up and slow down.

Bear in mind however that there is shallow water trim operation and then there is trailer trim operations. In other words you don't want to operate a U joint much past 40 degrees or so otherwise it starts working against itself.

 

[Bob Sander]

Once converted, there's no going back. I believe the 4 stroke outboards are what has pretty much outdated the formerly popular I/O's....

I love outboards.... until they break down. They are a royal pain in the azz to work on.

 

[ahicks]

I love outboards.... until they break down. They are a royal pain in the azz to work on.

I do a LOT of work on mid size Honda outboards (40-90hp) bringing them back from the dead. Seized, water in oil, blown lowers, whatever. At 70 years old now, I am WAY beyond handling some of the stuff handled 40-50 years ago easily. I can set an outboard on a work stand in front of me, pull up a stool and do ANYTHING that motor needs with tools an arms reach away.

Working on an outboard, as long as you are in no hurry (retired, I rarely hurry for much), can't get much easier.