Twin mercruiser 3.7 engine replacement

[borelca]

I have been having problem after problem with my twin mercruiser 3.7 165hp engines and thinking about replacing them with something else. The boat is a 28foot Fairbanks sportsfisher and in good shape. Dry weight of the boat is 8500lbs and currently gets up on a plane easily. I have read that the mercruiser 3.0 135hp engines are an easy swap because the gear ratio is roughly the same and mates up easily to the existing alpha one outdrives. Not sure if that is enough power though. Anyone out there know if 270hp will be enough to get up on plane? I don't need to go fast but just need to get it out of the hole and stay on plane.

 

[thumpar]

Re: Twin mercruiser 3.7 engine replacement

A 3.0 uses a different ratio. The 3.7l used the same ratio as the 6 cylinder engines.

 

[borelca]

Re: Twin mercruiser 3.7 engine replacement

Thanks, I was told that the gear ratios were close enough that it could be compensated for at the prop.

 

[thumpar]

Re: Twin mercruiser 3.7 engine replacement

You might be able to make up for the difference with prop but it may make it really inefficient in the end. I would go 4.3l. They use the same ratio, are a dime a dozen at a junk yard and make more power. All you would have to do is change out the core plugs. Either way the mounts will have to be redone and external parts sourced, so I would go bigger and think it would be cheaper in the end since the 4.3l is common and the 3.0l is a special application motor.

 

[MarkSee]

Re: Twin mercruiser 3.7 engine replacement

Welcome to IBOATS.

Your boat will weigh in a bit more than mine and I've got about 300 hp and with a Bravo 3 drive.

I'm thinking you might be able to get it on plane but long term may not be the best use of your money with less hp.

As mentioned, might want to see if can structurally modify the engine mounting systems for the 4.3s

Mark

 

[Eric 3.7LX Alpha 1]

Re: Twin mercruiser 3.7 engine replacement

what have you had for problems with the 3.7?

 

[Bondo]

Re: Twin mercruiser 3.7 engine replacement

You might be able to make up for the difference with prop but it may make it really inefficient in the end. I would go 4.3l. They use the same ratio, are a dime a dozen at a junk yard and make more power. All you would have to do is change out the core plugs. Either way the mounts will have to be redone and external parts sourced, so I would go bigger and think it would be cheaper in the end since the 4.3l is common and the 3.0l is a special application motor.

Ayuh,.... Great Idea, but bein' in-line motors are in the hull now,....

The Odds are, the crankshaft center-lines are Too Close to drop V-motors into it,...

 

[borelca]

Re: Twin mercruiser 3.7 engine replacement

Thanks guys, There should be plenty of room if I wanted to put in the larger motors. I have seen the same boat with 4.3s installed and still looked like room to spare. I guess I was thinking that the 3.0s would be cheaper and if they got the boat on a plane and went 22mph at 75% throttle then that would be the way to go. I was told that that the 3.0s could pretty much be dropped in with a little modification of the front engine mount and a new prop. Plus the savings in gas vs going up to the 4.3 would be nice.

The problem I had with the 3.7 is pretty much the same as everyone else. It overheated once and then caused the head gasket to fail. Also, the seals in the water pump started to leak like plenty of other people on this forum so had to do that repair. It was a remanufactured long block with only 400 hours on it but I'm afraid that these engines are just to problematic for me. I live in the pacific NW and cruise up into the San Juans and need something more dependable. I've lost most of the summer cruising trying to deal with all the stuff that goes wrong with these engines. Parts are getting hard to find so I might as well bite the bullet now and put reliable and repairable engines in it.