Mercruiser Engines

[Bigplumbs]

So still looking for my next boat 24-25 ish foot trailable Sports Cruiser.

I have posted about Diesel so now want to learn more about petrol.

I have a simple Mercruiser 3 ltr 135 hp and understand that. In the boats I am looking at I see:

4.5 ltr V6
4.0 ltr mpi
5.7 ltr V8
5.0 Ltr MPI

And a few others

Can anyone give me some idea of the main differences

Thanks

Dennis

 

[spannerman]

All V6's are 4.3 and are either carb 190hp, or injected 205hp & 230hp on the later MPI models.
V8's are carb 5.0 230hp & 5.7 260hp. Then you have injection in 5.0 and 5.7 in single and multipoint injection with similar hp range, and there a few models between but these are the main variants. If they have an Alpha drive then the seawater pump is in the drive, if they have Bravo drives then the seawater pump is on the engine. I'd go for an injection engine for easier hot and cold starts and no stalling, and a Bravo drive for smoother gear shifts. Thats MHO as a Mercruiser engineer and having only run V8's in my own boats.

 

[TheOrs]

V8's are carb 5.0 230hp & 5.7 260hp. Then you have injection in 5.0 and 5.7 in single and multipoint injection with similar hp range, and there a few models between but these are the main variants.

So, what's the difference between a standard V8 & a 'Magnum'?

TIA

 

[[2068]]

So, what's the difference between a standard V8 & a 'Magnum'?

TIA

From another forum:

"...the biggest difference between a standard 350 and a 350 Magnum (or 5.7 and 5.7 Magnum) was typically a mild bump in the cam and perhaps compression. For the most part the differences were (are) minimal. I've heard claims of forged internals etc. From the Magnums I've torn down in the small block realm none were forged and none had 4 bolt mains. The Magnum monicker was never directly related to an MPI motor, but an MPI motor could be a Magnum."

Some had 4-barrel carbs as well.

 

[IF-S]

The Ors
Power and torque
Dennis
Power, torque and fuel consumption.

 

[simonfraser]

You might want to know which variants are less trouble

 

[Bigplumbs]

You might want to know which variants are less trouble

That would be very useful does anyone know

Dennis

 

[julians]

I dont know too much about the v6 variants but the wet joint exhaust manifolds and risers on the older v8's are a weak point, after a few years running in salt water they can corrode and let water into the cylinders which results in a ruined engine. The way to avoid this is to replace the manifolds and risers every few years.

From around 2002 mercruiser changed the design of the manifolds and risers to a dry joint design so now if they corrode the water cannot find its way into the cylinders and doesnt ruin the engine. Its a much better design that results in an overheating situation rather than a ruined engine and allows much longer between replacing manifolds/risers.

However it appears that mercruiser didnt really shout about this design change so not many people are aware of it, so lots of people(on forums) still go on about manifolds and risers being a weak point even on newer engines.

As far as i know ( and i could be wrong on this bit) the volvo penta v8 (which is the same block as the merc v8) still uses the wet joint manifold design and still suffers from the weakness

 

[benchmark]

I have had only one mercruiser /drive combination and it ran without fault. I have a 5.0 L V8 with an alpha I gen II drive (2005 model)



Even as a carburetor model, it never missed a beat and is very forgiving . Virtually a bulletproof engine that likes to work i sail an avarage of 100 hrs per year with it , though i am lucky that my marina is brackish water with very low salt content hence corrosion was at a minimum to the raw water cooling system in my case . My immediate sailing waters have a salinity of only 0.2 - 1 % .

if you are located in sailing waters with normal or high salinity then make sure you get Mercruisers Seacore series which is a bit more resistant to corrosion in some places, also make sure you choose a closed cooling model to reduce the same problem.
Furthermore proper maintenance and service of the stern drive was a headache , very few mechanics know how to do it well enough and even fewer care to do it properly. in the end i learnt to do most of it myself but it is painstaking to change the throttle bellows , exhaust bellows and drive shaft bellows every 3 years as Mercruiser recommends.

All in all, i am satisfied with mercruisers engines and if properly cared for, is a good engine however since i purchased a Diesel boat with a straight shaft and fixed propeller ...i must say that the difference is clear, way much less hassle.

 

[spannerman]

From another forum:

"...the biggest difference between a standard 350 and a 350 Magnum (or 5.7 and 5.7 Magnum) was typically a mild bump in the cam and perhaps compression. For the most part the differences were (are) minimal. I've heard claims of forged internals etc. From the Magnums I've torn down in the small block realm none were forged and none had 4 bolt mains. The Magnum monicker was never directly related to an MPI motor, but an MPI motor could be a Magnum."

Some had 4-barrel carbs as well.

I have a 350 Magnum and another difference is they have roller type cam followers instead of bucket followers, also the ignition has a knock sensor and idle controlled via the ignition timing, all this even though its a carb engine.

 

[Fishtigua]

Just to say that Merc no longer sell the 3.0, the 4.3 V6 and the 5.0 V8. They have been replaced by the 4.5 V6. It's lighter than the 5.0 for the same power and a better package size. The 5.7 has now gone to 6.2.

You can still get factory rebuilt 4.3's and 5.0's which are brand new by any other name and good value for a repower. There are loads of 5.7's still around, one of the most popular marine engines ever built, so they will be supporting them for many years to come.

 

[Bigplumbs]

You can still get the 3.0 and the 4.3 from Repower Marine and the 3.0 is on Mercurys website ?

 

[Bigplumbs]

What would the fuel usage be like on a 5.7 over a 3.0 I would guess almost double. I was tending to steer clear of the big 5.7's but Looks like I was wrong to do so

Dennis

 

[spannerman]

My 5.7 in a 24ft weekend cruiser uses 34lph at 24kts and 70lph at 36kts! Guess what speed I cruise at...

 

[mlines]

With our 350MAG the £50 day outs we had with the old 3litre have become £80 day outs. However the grin factor of the V8 is worth it

 

[QBhoy]

Hi
There seems to be a bit of confusion here around the subject, thought I might try and clarify, from what I know and perhaps offer my own opinions...having had many variants of mercruisers and similar VP variants.
Not all v6 Mercruiser are 4.3's. There is a 4.5, as someone has pointed out already.
Mercruiser have apparently seen fit to move away from their relationship with Chevy engines.of this size..for the better, has yet to be seen.
Anyway, in your case, this may be of no consequence.
You won't go wrong with any of these engines really. They are all pretty bullit proof and have time and time again lasted for longer than the boats they are installed in...even in salt water. Proper annual maintenance and riser replacement when due and they are faultless.
Having had mainly carb versions of the 4.3 and 3.0, I can say that the 4.3 is a much nicer engine and well worth the extra money...if just for refinement alone. In some applications they are actually better on fuel too.
More recently I have a 5.0 V8 mpi. What an engine this is...it is unbelievably economical. Cheaper to run than a 4.3 carb and so much better at starting. The 4.3 mpi will be the same.
I would strongly urge you to go for an MPI engine if you can. More power, more economy and more modern. These are compatible with smart craft and other Bluetooth gadgets. This will show faults fuel economy etc.
Long story short...they are great engines...mpi versions have uprated power equivalent of the previous bigger models. Simple and cheap to service and come with the tried and tested Chevy reliability. They aren't the most popular boat engines in the world for nothing !

 

[QBhoy]

An example of fuel economy figures from today with the 5.0mpi;
Rpm:2400
Speed gps:26mph
Economy:20.9 litres per hour.

Incredible.

 

[Fishtigua]

The 3.0 may be on the website but just try ordering one!

Take care when getting any aftermarket repower unit, some of the standards of remanufacture do make us chuckle when it all goes bang.

 

[Bigplumbs]

With our 350MAG the £50 day outs we had with the old 3litre have become £80 day outs. However the grin factor of the V8 is worth it

That is useful information. I tend to spend about £30 on our 3.0 day outs so perhaps would go to £50 which is ok

Dennis