I/O (Sterndrive) Conversion to Outboards

[Scott Danforth]

outboards do have fuel coolers and oil coolers. however for the most part short of the Seven Marine 557/627 outboard motors, no, there isnt a heat exchanger.

 

[Lou C]

For both salt & fresh:
Self draining for winterizing
Able to tilt higher for shallow water
No concern with gas vapors in the bilge
Catastrophic failure of ujoints/driveshaft on an I/O can cause a dangerous water leak into the boat, this can’t happen with outboards…
You can’t have a failed cooling hose fill the bilge with sea water & nearly sink the boat with outboards; TJs can happen on inboards
Salt water main advantages are:
You don’t have to replace the manifolds & elbows every 5-7 seasons
Ability to tilt up to avoid corrosion and marine fouling
Engine has internal anodes to reduce internal corrosion
In general engine & add ons are designed to be in salt water and so the components don’t corrode as fast as similar items on an I/O boat.
To me the safety advantages are most salient and are true in fresh or salt

The only advantages of I/Os are the less expensive simpler GM marine engine and swim platform, it is a lot cheaper to repower an inboard.

I grew up with Chevrolet small blocks and know them well but as one of my former mechanic friends said I’d rather have my Chevy small block…in a Chevy!

 

[redneck joe]

Swapping a ob is less traumatic than an i/o block imo.

 

[Lou C]

True 4 bolts and it’s out. With I/Os you have 2 worries the engine & the transom/drive. That’s why some mechanics call them “double trouble”.

 

[redneck joe]

True 4 bolts and it’s out. With I/Os you have 2 worries the engine & the transom/drive. That’s why some mechanics call them “double trouble”.

Cpule screws for throttle linkage. Olny drawback would be if changing brands but still easier. And when I redid my floor that has its own space so pulling will be easier than normal.

 

[Stinnett21]

I'll add bellows, shift cables, u-joints, alignment, breaking trim sender wires, multiple avenues for leaks requiring yearly drive pulls and the ability to be a circus contortionist.

 

[flashback]

outboards do have fuel coolers and oil coolers. however for the most part short of the Seven Marine 557/627 outboard motors, no, there isnt a heat exchanger.

I just spent 20 minutes with a video about 7 marine. Never heard of it. Pretty awesome.

 

[Scott Danforth]

I just spent 20 minutes with a video about 7 marine. Never heard of it. Pretty awesome.

Too bad Volvo Penta bought them to squash them

 

[tphoyt]

I have never seen a seven marine motor in person but years ago I did watch a video on them and was very impressed. I believe they hard the largest hp for an outboard at the time and seemed like they were going to do well but as we all know it takes a lot to break into the outboard market and compete with what’s considered the best of the best.

 

[Pmt133]

I remember those seven marine units. From what I remember they were quite heavy. (1100 lbs?) I've never seen one in person either.

 

[harringtondav]

The only advantages of I/Os are the less expensive simpler GM marine engine and swim platform, it is a lot cheaper to repower an inboard.

I grew up with Chevrolet small blocks and know them well but as one of my former mechanic friends said I’d rather have my Chevy small block…in a Chevy!

I made the twofootitus upgrade four years ago. Merc 180 hp 4.3LX to a VP G5 4.3 250 hp.
I compared several brands of 18-20' BRs. In all cases where the boat offered both I/O or O/B, the O/B model at the same power was considerably more expensive. Also the O/B version offered less hp than the highest hp I/O.
So I went with another I/O. Family would have disowned me if I didn't get a swim platform.
Now I'm stewing in my own juices for the decision. The VP is shoehorned into a Regal 1900 ESX. Engine pull requires removing the one piece exhaust manifold/risers. Last summer I gave up changing #4 & #6 plugs to lack of access. I'll give it another go in the spring, but I may have to pull the starboard manifold to get the job done.
Most decisions involve trade offs. ....then you live with them.

 

[Lou C]

I made the twofootitus upgrade four years ago. Merc 180 hp 4.3LX to a VP G5 4.3 250 hp.
I compared several brands of 18-20' BRs. In all cases where the boat offered both I/O or O/B, the O/B model at the same power was considerably more expensive. Also the O/B version offered less hp than the highest hp I/O.
So I went with another I/O. Family would have disowned me if I didn't get a swim platform.
Now I'm stewing in my own juices for the decision. The VP is shoehorned into a Regal 1900 ESX. Engine pull requires removing the one piece exhaust manifold/risers. Last summer I gave up changing #4 & #6 plugs to lack of access. I'll give it another go in the spring, but I may have to pull the starboard manifold to get the job done.
Most decisions involve trade offs. ....then you live with them.

About 3 years ago my brother moved back to my area (North Shore Long Island NY all salt water) and wanted a boat again. He wound up with a 2020 Chapparal 20' with the Merc 4.5 V6. Very nice driving boat, nothing to complain about there, but the engine accessiblity was bad except for oil changes and the quick drain. Any other repair would have been a horror show, and there's the cat converter exhaust which in salt water is such a financial liability, I will NEVER have one. Boat was fine though till one day (moored in salt water) it started running hot, the Merc Guardian system kicked in to limit RPM. All it was, just a bit of marine fouling, I showed him how I hang over the swim platform and rod out the water intake holes in the lower unit. But at that point he could see the writing on the wall and traded it on a similar boat with a Yamaha 4 stroke. There is a swim platform, just not the full width one you can have on I/Os.
I told him, here's the thing, that drain system clogs, you're hanging upside down to clean the damn drains. Starter goes, engine pull. Steering actuator leaks, engine pull. Cat converter exhaust has to be changed at year 7-8 let's say, and even if I did it for him, it could be as much as $6000 in parts. Then every year worrying if the easy drain clogged or not. Just not worth it here.
I/Os made sense when:
OBs were loud and smelly
Inboards were simple carbed GM marine engines. Have you checked Merc's OEM or Volvo's OEM parts prices, they are no longer really cheaper than outboards.
Boat builders didn't surround the engine with molded in 'glass for all the fancy cushions no one needs and make the engine impossible to get at.
I blame the boat builders for this, the cat converter exhaust, well you know who I blame for that. And so it goes.

 

[tpenfield]

In the 'better late than never' catagory . . .

.
Maybe I'll pick up a few pointers . . . or find out if I am making a blunder.

 

[Pmt133]

As I say at work... that sounds like a problem for future me.

 

[tphoyt]

I’m sure there is some great and interesting info to be read.