Dreaded 3.7 replacement

Hi guys. One of your members suggested that I poke my head in here to ask my question about helping a buddy who made the misguided error of buying a boat with a 3.7 liter Merc. with Alpha drive. That motor is in need of serious repair or replacement, and I'm trying to help him out. I've owned only outboards and Volvo stern drives, so I'm not well versed on the ins and outs of mercruiser. So here I am.

First and foremost, theres a guy right down a road with a boat my friend can buy for very little money. This boat has the 120 merc and older style outdrive. The one with the lifting ring cast into the cap. Is that drive a straight swap with the Alpha? IE: Could we pick up that boat, make whatever motor mount mods are needed to get the engine fitted to my friends boat, then mount up the drive?

Or, I can put some time in to try to find another engine. 3.0 or 4.3, but as I understand it, the 4.3 is compatible with the 3.7 Alpha due to gear ratio, but is not as easy to bolt up due to greater difference in engine mounts? The boat is a 88 Raven cuddy, which was available with the 4.3 as I understand, so maybe the mounts will be there?

Any guidance or suggestions would be welcome. (Yes, I know his best bet would be to sell the boat and start with a boat with a better power plant, but that option is off the table)

Edit: Original problem that lead up to all this is #4 cylinder being full of coolant. Haven't investigated why yet, but I haven't found many people who recommend repair the 3.7 vs replacing. If you gents want to talk me into repair, I'm all ears.

First off,

the coolant in cyl 4 is a common issue. Most likely is the exhaust manifold/coolant tank. the material errodes and coolant gets into exhaust port and makes it way into cyclinder. It also could be a blown head gasket


So remove all exhaust components and pressure check EACH SEPERATELY for leaks. If you find the leak replace the part and all may ok.
With the exhaust manifold off, pull the plugs and get the coolant out of cyclinder. When sure it is dry or as close as possible do a compression check to see if there is a head gasket leak.

Second. DO NOT GO BACKWARDS for older boats with older components.................. unless you know all the differences it is a painful exercise.

third, due to the 4 cyclinder motors use a front motor mount (120,130,470 etc) and the inline six (older) there are no side stringers to mount a V6 or V8. So no V6 can be adapted without adding stringers.......good luck with that.

The typical 470 is a minimum of 165-170 hp, a 4 cyclinder 120 is at best 120 hp.........boat will be a slug............

Do a craigslist search for the 470, you may be suprised what you find.

hope this helps........

I'm actually pretty glad to finally talk to someone who recommends repair rather than replacement. I'd much prefer to go that route. To most folks, owning a 3.7 is like owning a Bayliner (which I own) Tell them you have a problem and they tell you to sell it and get something better.


Anyhow, your response leads me to ask a few questions. One, I was under the impression that the power difference between the 3.7 and 3.0 wasn't that great due to the 3.7 being rated at the crank while the 3.0 is rated at the prop. And while the 3.0 is no power house, I have been in boats of similar size to my friends (19' cuddy) that were equipped with the 3.0 and they were slightly underpowered, but still suitable for his needs. This is his first boat, and he has small children. Tubing, skiing and wake boarding can wait til his second boat when his kids are older. So with that in mind, if worse came to worst, would the 3.0 really be a terrible idea as a repower option? Not that I doubt you're knowledge, I'm just curious if you mean the boat would be a slug in that it would be too underpowered to plane, or if you're talking more about more of a personal preference type thing.


All that hat said, I'd still prefer to repair his 3.7 if it can be done reasonably and he have a reliable boat. I'll try to pull the exhaust components tomorrow and get a look at everything. I'm still a little fuzzy on how his cooling system works, it's vastly different from the raw water cooled boats I've always had.

You said a 120. Not a 3.0.
Considering it has a I or R outdrive it is a 120 hp
Current 3.0 moters are closer to 140 hp.

There is no comparison between the 3.0 and the 470. Just look at the size difference.
It like a small block vs a big block.

As far as the water flow...get a manual. If I can tomorrow I will post a pic of it but it may not be easy to read.
Send me a message with your email and I can send a better pic of the water flow diagram.

Knowing the watet flow realy is not important. If you can get a hold of a radiator pressure tester you can prssurize the system while still on the motor. You may not be able to distinguish a manifold leak or a head gasket leak though.
A compression check will tell a head gasket leak.

Justin... some people will continue to ask the same question and ask for advice until they finally hear what they've been wanting to hear from the beginning.
Don't fall into this category.

It is fact that Merc's 470 poses issues, and has for some time.
Had it not.... it would have been in production for more years than it was.


.

So Ricardo here, Rick on the BOC. You have any other aliases? ;-)

I'm not really asking so I'll finally hear what I want to hear. I'm just trying to get various view points. You've never given me anything but perfect spot on info. And as much as I'd like to say uncle and chuck this motor, I'm thinking my best shot at getting it wet in the near future is going to be repair. It sounds like swapping in the 4.3 would be a mess, and swapping in a 3.0 would require a drive change. Short of selling the boat and picking a different one, I'm running out of options. If it were my boat, I'd be taking a different approach. But the boat belongs to a friend and I'm just trying to get him on the water. Truthfully, if I can scab it together and he can use it the 8-12 weeks of remaining season we have, that's all it really needs to do for now. Then we can worry about next season later.

What would you do in my position (Not just Rick, I welcome anyone answer to that question). Getting rid of the boat isn't one of the options, I can either try to fix what I have, or pull and replace the motor. Keep in mind, my guys budget isn't unlimited.

Understood!
We all have your best interest in mind... and I want to be realistic with you. Had your friend done his research, he'd have passed on this boat.

But... let's move forward, and see what we can do to salvage this engine.



.

Rick, it never crossed my mind that you'd have anything less than my best interest in mind! If not for you, I'd still be in the engine compartment of my Bayliner with a stethoscope looking for the source of the strange growling noise. ;-)

So had some time today to yank the manifold and coolant tank off this barge. Now to figure out how to test it. Looks like I'm going to need to cobble something together to plug the holes, and install get some pressure in it. Any advice there would be welcome, otherwise, I'll just have to go through my parts bins until I find stuff that will work.