I/O Characteristics

[IslandExplorer]

Hello, I am looking at getting a larger boat with an old (1970's era) Mercruiser I/O, probably pre-alpha 1, likely with the Merc 160 inline 6 GM motor. All my previous boats have been outboards. What I am wondering is: can you run an I/O with it tilted up a ways like you can with an outboard? I have read many conflicting accounts of this, some saying you just can't without damage or risk of some kind. Now I know many of these old I/O's don't tilt up anywhere near as far as an O/B obviously but is it true that they can't be run in gear tilted up? Like in a shallow area where you are just trying to be careful in case you bump the bottom? Is the universal joint in the out-drive an issue or something?
Are they more vulnerable to damage if you did hit something at low speed? I go in shallows a lot.
Please explain with as much detail as you are willing to provide bc I really want to understand what I will be getting into.

 

[Scott Danforth]

What I am wondering is: can you run an I/O with it tilted up a ways like you can with an outboard?

no

 

[nola mike]

no

Huh? You can, you just can't go very fast.

 

[KD4UPL]

You can trim the drive up a ways to gain a bit better draft. If you go beyond a certain point it puts the U-joint in a range that it doesn't like. You can run it like that VERY Slowly and briefly but I wouldn't do it all the time.

 

[ahicks]

If you're running the shallows a lot, I have to wonder why you are considering an I/O, let alone an older one?

All else being equal, an outboard, being lighter, will have the shallower draft.

And worst case, you hit something, I would MUCH rather be looking for parts to fix an outboard than an I/O...

 

[poconojoe]

I don't know much about jet drives, but I would think they would be a better choice for shallow water. That's what is common on the Delaware River here in Pennsylvania.

I/O's can be trimmed up, but there is a limit to how far up. If you raise it beyond that point while the engine is running, you risk damaging the u-joints.

There is a trim limit device on the drive, and if adjusted properly, will limit how far up it will go. Trailer trim position goes beyond that for trailering purposes.

I have an I/O and if I were to do it all over again, I would go with an outboard, hands down, no questions about it.
Too much maintenance and winterizing with an I/O. Then there's the stupid bellows, what a dumb idea. A set of thin rubber boots that, if they leak, can sink your boat. Why would someone engineer a system that has a big hole in the transom below the waterline? If only I was better informed when I bought my boat.

Run far away from that I/O my friend.

 

[briangcc]

I've owned both and hands down, if I was to do it again, it'd be outboard power.

My cousin has a large(r) SeaRay deck boat with I/O and he's told me that **IF** his wife and daughters would allow him, it'd be an outboard - they like the sunpad. This after he's replaced his prop several times (hit submerged hazards), replaced his outdrive (same time as prop), and had his engine torn down due to sucking in a fishing net. Same cousin also has a Sylvan outboard that sees alot of fishing duty.

As you tilt the outdrive up, you're exposing the bellows to underwater hazards. So **IF** you were to cross a log with the boat, and it popped up, it could potentially hit the bellows, then you're in a world of hurt and hopefully have a couple bilge pumps to keep you afloat to the dock.

I've run in 2' of water, at idle, with the I/O tilted up (still in range on the trim gage) although it definitely doesn't like it. Usually at that point I kill the engine and drop the trolling motor.

 

[Lou C]

A boat that old is going to have a bunch of problems, the Merc stuff won't be the worst of it, but even Merc discontinues parts, there are going to be a number of NLA parts for the engine accessories and the drive and transom mount. I would not do it just for those reasons.
As far as trimming an I/O up for shallow water use, well you can safely trim it up half way and then your boat most likely is only drawing 2.5' to 3' of water, and half way up won't stress the ujoints if you keep it at idle, or slightly above.
I too will get an outboard boat next time, due to wanting less maintenance easier winterizing, etc. But they have their draw backs too, namely very expensive parts, but most feel its a fair trade off for the benefits....much less maintenance, safer, not much to do for winterizing, etc.
The ONLY way I'd get another I/O boat is if it is pre-cat converter, if it can be swapped back to a 4 bbl carb and the engine compartment is wide open for maintenance access. I would start with a new 5.7 Vortec and add closed cooling and a remote oil filter mount, these 2 add ons, with a wide open engine compartment, make life with an I/O much more tolerable. You can change oil very easily and the closed cooling allows you to winterize with the winterizing tank easily. No pulling out seats, crawling around in the bilge, dropping drain plugs in the bilge water, all the other treats of I/O maintenance.

 

[JASinIL2006]

I think outboards are butt-ugly on bowriders, but I have to confess, if/when I get a new boat, I will strongly consider an outboard for all reasons mentioned above.

 

[poconojoe]

A boat that old is going to have a bunch of problems, the Merc stuff won't be the worst of it, but even Merc discontinues parts, there are going to be a number of NLA parts for the engine accessories and the drive and transom mount. I would not do it just for those reasons.
As far as trimming an I/O up for shallow water use, well you can safely trim it up half way and then your boat most likely is only drawing 2.5' to 3' of water, and half way up won't stress the ujoints if you keep it at idle, or slightly above.
I too will get an outboard boat next time, due to wanting less maintenance easier winterizing, etc. But they have their draw backs too, namely very expensive parts, but most feel its a fair trade off for the benefits....much less maintenance, safer, not much to do for winterizing, etc.
The ONLY way I'd get another I/O boat is if it is pre-cat converter, if it can be swapped back to a 4 bbl carb and the engine compartment is wide open for maintenance access. I would start with a new 5.7 Vortec and add closed cooling and a remote oil filter mount, these 2 add ons, with a wide open engine compartment, make life with an I/O much more tolerable. You can change oil very easily and the closed cooling allows you to winterize with the winterizing tank easily. No pulling out seats, crawling around in the bilge, dropping drain plugs in the bilge water, all the other treats of I/O maintenance.

Good point on the closed cooling.

 

[IslandExplorer]

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.

 

[IslandExplorer]

Has anyone here installed the freshwater conversion setup to keep the saltwater out of the engine? Is it basically just a heat exchanger and I'm assuming an additional water pump (one for engine coolant, out-drive one stays for saltwater) or what? Seems like that would be very worthwhile if I decided to stay with the I/O.

 

[Scott Danforth]

Has anyone here installed the freshwater conversion setup to keep the saltwater out of the engine? Is it basically just a heat exchanger and I'm assuming an additional water pump (one for engine coolant, out-drive one stays for saltwater) or what? Seems like that would be very worthwhile if I decided to stay with the I/O.

On a new motor, yes

On a used motor, dont do it

 

[MRS]

I think outboards are butt-ugly on bowriders, but I have to confess, if/when I get a new boat, I will strongly consider an outboard for all reasons mentioned above.

I have always had I/O on my boats but did a 180 got a pontoon with a 4 stroke outboard love my butt-ugly outboard. It is quite and no crawling around boat to winterize looks beautiful now to me.

 

[ahicks]

I have always had I/O on my boats but did a 180 got a pontoon with a 4 stroke outboard love my butt-ugly outboard. It is quite and no crawling around boat to winterize looks beautiful now to me.

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....

 

[H20Rat]

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.

 

[MRS]

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.

All I have to do with 4 stroke outboard is lower it to drain water wipe down the outside and put my cover on it done. If I do want to take out in the winter I take cover off and go. Nothing wrong I/o if you love them.

 

[IslandExplorer]

On a new motor, yes

On a used motor, dont do it

Why not on a used motor?

 

[IslandExplorer]

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.

I like all the points raised here and I would surely love to have one of the nice quiet 4 stroke Yamaha, Honda, etc. outboards but the price point, for someone like me, is a Huge barrier. I'm more the type to get a junkyard engine if I had to and go through it myself over the winter in my barn to save the money. I bet if I landed some 6 figure job I'd change my tune though! haha All my motors have been fixer uppers, some even "unrepairable" given up on by multiple mechanics like my 1979 Evinrude 4hp that runs awesome and my previously completely submerged 1988 Johnson 70hp. I'd actually be a bit afraid of the newer motors bc I like understanding the whole system and with an old carbed motor- I/O or outboard- that is much easier, for me at least. Especially if you need to do on the water repairs. I don't like taking a jet out on a carb when the boat is moving up and down in the waves but I've definitely been there and got home bc of it. The old 70's I/O's engine-wise appear to be even simpler than the relatively crammed in outboards. That Mercruiser 165 seemed especially open due to the skinny inline 6. If they can operate ok trimmed up for shallow beach approaches and whatnot then I don't see why I wouldn't be ok with it assuming I find the boat I'm looking for and it has an I/O. The high dollar 4 strokes cost more than the whole boats I'm looking at after all!

 

[Lou C]

Why not on a used motor?

internal rust flakes from corroding cast iron will clog the heat exchanger.