Merc 4.3

[jimmbo]

Are Merc 4.3 inboards problematic?

I am not a fan of the 4.3 as it is a small engine, and a V6 to boot. I find it to be low on Torque, and an Albatross on boats over 16 ft
It's main Achilles' Heel is that the Intake manifold, needs to be drained when Winterizing. This is a Procedure that is quite often missed the first time someone winterizes one of these. I doubt they repeat that Omission on future Winterizations.

 

[poconojoe]

I am not a fan of the 4.3 as it is a small engine, and a V6 to boot. I find it to be low on Torque, and an Albatross on boats over 16 ft
It's main Achilles' Heel is that the Intake manifold, needs to be drained when Winterizing. This is a Procedure that is quite often missed the first time someone winterizes one of these. I doubt they repeat that Omission on future Winterizations.

Just out of curiosity, what is wrong with an engine being a V6?
Maybe you're just a V8 guy? I get that. Maybe you just like more power, but there's a place for smaller engines.

My bow rider is 18.5 in length and the 4.3 has no problem handling things. 45 mph on the water is plenty fast for me. Plus, it jumps up on plane in only a few seconds.
In fact the very same boat also came with a 3.0.

 

[Scott06]

Just out of curiosity, what is wrong with an engine being a V6?
Maybe you're just a V8 guy? I get that. Maybe you just like more power, but there's a place for smaller engines.

My bow rider is 18.5 in length and the 4.3 has no problem handling things. 45 mph on the water is plenty fast for me. Plus, it jumps up on plane in only a few seconds.
In fact the very same boat also came with a 3.0.

Yes has been my experience as well 4.3 vortec in a up to about 20 ft works well.of course more power is nice and every boat line has low buck 3.0 or 4.3 carb 5.0 in a bigger boat price point offers. 4.3 has proved to be inexpensive durable and powerfull. way more power per engine size and wt vs the engines it replaced, plus parts are widely available

 

[Lou C]

Agreed and when I was paying $6.00 a gallon this summer it was nice to have 2 less cyls to feed. The 4.3 & Quadrajet combination is very economical because of the small primaries. In my boating area I can rarely go faster than 30 mph anyway. However I wouldn’t be against a 5.7 upgrade when I repower. I don’t have to change the Y pipe & I have 2 Cobra drives that have a 1.62:1 gear ratio which might be fine with a V8.

 

[Lou C]

I am not a fan of the 4.3 as it is a small engine, and a V6 to boot. I find it to be low on Torque, and an Albatross on boats over 16 ft
It's main Achilles' Heel is that the Intake manifold, needs to be drained when Winterizing. This is a Procedure that is quite often missed the first time someone winterizes one of these. I doubt they repeat that Omission on future Winterizations.

The intake issue applies only to the later Vortec engines not the older pre Vortec ones like my 1988. I think they increased the size of the water passage to offset the lack of the exhaust crossover that the pre Vortecs had. So one more drain plug.
Durability wise they are very good; my short block survived a bad overheat & blown head gaskets 3 years later. A pair of reman cyl heads new gaskets & head bolts & I was back in business. Total parts cost was just under $800. Hard to beat that!

 

[poconojoe]

I can go out for an enjoyable day on our 13 mile long lake and only use about 7 gallons of gas with my 18.5 bow rider 4.3 Mercruiser.
No complaints on fuel consumption by me.

 

[jimmbo]

" that have a 1.62:1 gear ratio which might be fine with a V8."

1.62:1 will work with a 5 liter, but something in the 1.5:1range is better for a 5.7, unless you are in the 23 ft range. At that length, a Big Block should be under consideration

 

[lonestarnut]

No.

Why do you ask?

I just bought an Islander w/ a 4.3. Its my first inboard, so I’m a little nervous

 

[Lou C]

I just bought an Islander w/ a 4.3. Its my first inboard, so I’m a little nervous

Compared to outboards?
There’s the good:
simple engine & inexpensive parts
and not so good:
sometimes difficult access and the issues that arise from deferred maintenance. Once you learn how to do all the services they need to stay reliable they aren’t that bad…as long as the boat has good access….

 

[nola mike]

It's main Achilles' Heel is that the Intake manifold, needs to be drained when Winterizing. This is a Procedure that is quite often missed the first time someone winterizes one of these. I doubt they repeat that Omission on future Winterizations.

The intake manifold doesn't need to be drained.

 

[jimmbo]

Every 4.3 I have ever seen has to the the Intake drained

 

[Lou C]

The pre Vortec intake with 12 bolts drained when you drain the engine. The Vortec intake with 8 bolts has a larger water passage that added the extra drain plug in front. I guess these could trap water depending on the angle of the engine in the boat. The water passage in the Vortec was larger than the one in the Pre Vortec.I think this was to heat the area under the carb or TBI unit to prevent carb icing. The Pre Vortec had the exhaust crossover to do this so the water passage didn’t have to be as big. At least I think this is why GM designed it this way….

 

[stresspoint]

i recently bought a Maxum with a 4.3 and encountered a few problems that were pretty much normal for any inboard marine engine , mostly they were due to lack of maintenance by PO and lack of knowledge on the 4.3 by myself .
i learned lots about these little motors i ended up getting over 6k RPM out of mine . ? how long it would have lasted is another story , but it was strong when it was up there and nothing sounded like it was going to break . .

Q ,are they a good motor ,A in my experience , they are built as strong as a SB V8 and use many of the same parts so YES a solid little motor. Q, Problematic , in some respects , they could be, but as i found with upgrades to later model stuff they are a strong little donk for a boat motor and they have a very unique sound when they a cranked up .
they don't like water in the oil so maintenance to the cooling system ( as with any inboard) is a must ,

 

[Lou C]

The main difference is the split journal crankshaft, due to harmonics set up by this design they really shouldn't be revved over 5000 rpm. I'm not sure if the balance shaft on the '96 and newer ones mitigates this or not.
Other than that, they are just as durable as a V8. In fact I have heard of the typical failures (usually neglect related, bad exhaust, over propped, etc) but how often do you hear of a 4.3 crank failure? I've never heard of one and I've been on this board like 20 years.
Not only that if you follow the Chevy Blazer (S-10 series) and Astro van boards, which used this engine many years, the failures that happened were due to the crappy gaskets used on the Vortec series (V8s had the same problem) and other add ons like the oddball EFI system that GM cobbled up. Carbed versions were very reliable and actual mechanical failures rare.
As I said in previous posts if the design was flawed why would Mercruiser spend the cash to build their own version right down to the exact same crankshaft design (split journal) with the balance shaft. The could have started with a clean sheet of paper but didn't. I guess they thought after using it for 35 years it was good enough!

 

[Scott Danforth]

I just bought an Islander w/ a 4.3. Its my first inboard, so I’m a little nervous

There have been 7 generations of 4.3 since 1985

Need to narrow it down a bit closer. as stated above. Maintained 4.3s will last many thousands of hours.

 

[jimmbo]

Even with an evened out firing order, a V6 has some serious Imbalances, I am surprised they don't shake the layers of Fiberglass in a hull apart.

 

[flashback]

It was a reliable motor in my 89 S10 , never had one in a boat. I have a V8 preference and I have enjoyed this thread! It gave me 200k in the truck.

 

[Lou C]

Even with an evened out firing order, a V6 has some serious Imbalances, I am surprised they don't shake the layers of Fiberglass in a hull apart.

I bet you had 1 or 2 older GM cars with the odd fire Buick 231 cu in V6, because what you are saying is true of them, however, the even fire split journal crankshaft was used on the 4.3 from the time it came out. There were other V6s from Chevrolet that used what was called a semi even fire crank, the 200 and 229 V6s, but the 4.3 used a true even fire crank. Those smaller V6s probably weren't as smooth as the 4.3. Now if you tried a Blazer with the 4.3 & balance shaft (96 and up) I'd be surprised if you could feel any difference between it and a V8. I think that you're lumping together all GM 90* V6s, they are not all the same.....
And in boats they use soft engine mounts that all but damp out any imbalances that are left....
Latest version of this design, actually now built by Mercruiser, in 4.5 liter displacement and 200 and 250 hp versions, is indistinguishable from a V8, that I can tell you from experience because I drove my brother's 2020 Chapparal with the 200 hp 4.5.
Remember Mercruiser is still using a refined version of the 4.3, even fire crank and balance shaft but with more modern electronic engine management.

 

[Bondo]

with the 4.3 & balance shaft (96 and up) I'd be surprised if you could feel any difference between it and a V8.

Ayuh,..... I think that's 'bout '94,..... Vortec heads in '96,.....

My '94 w/ bal. shaft has better than 2,000 hours on it, sittin' on a dolly, waitin' to get dropped into another hull, right now,.....
Great motors,.....

Got the ole Buick/ Jeep V-6 in my CJ5,....

 

[Lou C]

Ayuh,..... I think that's 'bout '94,..... Vortec heads in '96,.....

My '94 w/ bal. shaft has better than 2,000 hours on it, sittin' on a dolly, waitin' to get dropped into another hull, right now,.....
Great motors,.....

Got the ole Buick/ Jeep V-6 in my CJ5,....

Yep you were right about the year of the balance shaft, the 4.3 is actually a popular swap into CJs, nice & compact. A nice 4bbl 4.3, with a Turbo Hydramatic 350 would make a nice combo in a CJ Jeep.