4.3 Chevy

tonyjh63

Petty Officer 1st Class
Joined
Apr 23, 2013
Messages
242
Hypothetically, if I were looking to replace my 4.3 Mercruiser (1999) with a used 4.3 Chevy engine, any tips on what to search for? Particular years to avoid, etc.?
I may have a cracked block, cracked head, or hopefully, just a blown head gasket.
Thanks!
 
Last edited:

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
Ayuh,..... Ya Don't want a 1985,....

I'd go with newer than 1996,....
 
Last edited:

Scott06

Vice Admiral
Joined
Apr 20, 2014
Messages
5,542
Truck engine 96 and newer with vortec heads matching your existing boat engine. Truck cam is close enough to marine to keep, if car engine swap in marine cam. Strip it to long block swap over marine oil pan, put in new marine head gaskets , and put in brass or stainless core plugs. Swap over your water pump, accessories, intake , fuel and ignition components.

sounds like you may have frost damaged engine? If so inspect intake water cross over and exhaust manifolds as well.
 

tonyjh63

Petty Officer 1st Class
Joined
Apr 23, 2013
Messages
242
Truck engine 96 and newer with vortec heads matching your existing boat engine. Truck cam is close enough to marine to keep, if car engine swap in marine cam. Strip it to long block swap over marine oil pan, put in new marine head gaskets , and put in brass or stainless core plugs. Swap over your water pump, accessories, intake , fuel and ignition components.

sounds like you may have frost damaged engine? If so inspect intake water cross over and exhaust manifolds as well.
Well honestly, I'm not sure what's going on...long story, but here goes:
Back in October, I forgot to put my plug in the boat, wound up getting towed in. Later, engine started and idled fine, but I discovered water in my oil. Took it to a shop, and mechanic immediately diagnosed that my problem was the "foghorn" style manifolds/risers that Mercruiser put on late-90s engines for only about 4 years (apparently a bad design which corroded too quickly?).
I had him replace with a new updated kit, and it supposedly cranked up and ran fine. When I went to pick it up the next day, he said he had cranked it up again to check for water intrusion, and after a minute or so, it sputtered and died. He then discovered water in the oil again. So he's thinking blown head gasket (best case, scenario?), cracked head, or cracked block.
Last I talked to him, he said he took out the spark plugs, unhooked the outdrive, but can't get the engine to turn over.
He's now on vacation 'til the first of the year, and will get back to it then.
Thoughts, theories? Thanks!
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,581
Your guy is a parts changer.
Replaced exhaust before knowing what the problem is.

If there was no running issue until the water intrusion, then its not a head gasket. Most likely its bearings and/or cylinder walls are rusted. If this is the case, the motor can be overhauled for not a lot more then the junk yard motor
 

tonyjh63

Petty Officer 1st Class
Joined
Apr 23, 2013
Messages
242
Your guy is a parts changer.
Replaced exhaust before knowing what the problem is.

If there was no running issue until the water intrusion, then its not a head gasket. Most likely its bearings and/or cylinder walls are rusted. If this is the case, the motor can be overhauled for not a lot more then the junk yard motor
No, the engine ran great all summer, cranked and idled fine once towed back to the dock, and the same 'til I took it to him.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,465
No, the engine ran great all summer, cranked and idled fine once towed back to the dock, and the same 'til I took it to him.
Ayuh,....... It appears to be that the root problem, is him,......

We're pretty much diy'ers in here, so yer options are to gather a tool kit, 'n let Us talk ya through the issue,.......
Or,.....
Find a Boat Mechanic that knows Mercs,......

I will give 'im credit for sellin' ya the new exhaust, especially if they're the current issue dry joint system,.....
Those ole batwings, or foghorns as you say, are a hydro-locked destroyed motor waitin' to happen,.....
Swappin' 'em out is a blessin',....

The guy just ain't a "Diagnosin' Mechanic",....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,304
If you need a 4.3, any 1996 and later 4.3 motor from a truck or a forklift would work. You are only using the shortblock as the waterpump, accessories, electrics, manifolds and induction must be marine
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Well honestly, I'm not sure what's going on...long story, but here goes:
Back in October, I forgot to put my plug in the boat, wound up getting towed in. Later, engine started and idled fine, but I discovered water in my oil. Took it to a shop, and mechanic immediately diagnosed that my problem was the "foghorn" style manifolds/risers that Mercruiser put on late-90s engines for only about 4 years (apparently a bad design which corroded too quickly?).
I had him replace with a new updated kit, and it supposedly cranked up and ran fine. When I went to pick it up the next day, he said he had cranked it up again to check for water intrusion, and after a minute or so, it sputtered and died. He then discovered water in the oil again. So he's thinking blown head gasket (best case, scenario?), cracked head, or cracked block.
Last I talked to him, he said he took out the spark plugs, unhooked the outdrive, but can't get the engine to turn over.
He's now on vacation 'til the first of the year, and will get back to it then.
Thoughts, theories? Thanks!
If the engine did not overheat, the likelihood of a blown HG is quite low. Sounds like you got water in the oil because the plug was out, mechanic concluded it was from bad one piece V6 manifolds (could be true but in this case could also NOT be true) so he replaced those. However some of the kits I have seen (Barr) use the wet joint system where in if the gaskets between the manifold and elbow are not high quality they leak water into the manifolds and you are back to square one. The problem with this situation is the longer the oil stays in the oil the worse the internal damage can be.
As an example about 5 years ago my engine blew both HGs but that was almost certainly from a previous overheat 3 years before that (combined with age & salt water use). Had water in one cyl and in the oil, took me a couple days to figure this out as the boat was on the mooring. Well I blew out the cyls, fogged it multiple times, changed oil 3 times, got the water out. Then took it apart, found cracked heads in addition to the blown HGs. Cyls not rusted though due to prompt drain and fogging. So I put it back together with reman heads, new gaskets and head bolts and its running as well as always still 4 years after I fixed it. These engines are tough, easy to work on and parts are cheap and plentiful. I might not give up so fast.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
Started with this....4.3 starboard cyl head removal.JPG
then bought a set of these:
4.3 reman cyl head 2.JPG
And put it all back together:
re-assembling the old 4.3.JPG
Added a center riser exhaust conversion while I was at it, since the old OMC one piece batwings (same idea as the Merc foghorns) were long since NLA...
4.3 Center Riser Exhaust Conversion.jpg
 
Top