Vortec 4.3 cracked block ... automotive swap?

No I have not. The tropical water here is evil. They say the salinity of sea water varies little but I would disagree with that.

I rins my raw water cooled fresh system after every run and drain exhaust. I don't have any sea water after the sea cock.

 

there are thousands of raw water cooled inboards in australia, gonzo is right . marine blocks are known as strong blocks, referring to the high nickel content. if you use an auto conversion just make or buy a heat exchanger.

 

Very interesting, but I have serious doubts.
Yamaha in their brief marine history used olive green GM blocks straight from the plant in Mexico, the very same ones that went into vehicles and/or industrial equipment.
The bulk of Merc boat engines was the 3.0 straight 4 block, only used in boats except for a few compressors and generators.

The raw water cooling does a lot of damage to all grey cast blocks. Merc installs a low temperature thermostat (70 C.) so the damage will not show before the warranty period is over. Anyhow, the first parts to fail due to corrosion are not the blocks but the manifolds cast from the same material.

 

no doubt, true marine blocks are high nickel blocks. even the old volvo b20 and b30 engines had a specially cast block for marine use. low temp thermostats are to prevent salt build up in the engine. nothing to with warranty. no salt water cooled engine, outboards included can run over 65 degrees c .

 

Please explain how a low working temperature can prevent salt build up in an engine. My sugar dissolves better in hot tea than in cold.

Low engine temperature makes a dirty, inefficient engine so there must be a better reason than salt build up for Merc to keep on selling units with 70 C. thermostats.
I think they use blocks from ASTM A48 grey iron because that is the most common, cheap material. I've seen Merc engines -used only in summer seasons- where the walls between cylinders were almost eaten through by corrosion. Allowing the working temp to reach 90 C. would certainly speed up that process (in fact any chemical process).

 

the way i understand it is that salt water above 65 deg deposits the dissolved salts on the water jacket walls like the calcium and mineral buildup kettles get from boiling water. when you hear people talk about salted engines it means the cooling passages are blocked with salt from running to hot. raw water cooled engines can never be as efficent as closed cooling , you are correct. i don't know why you think marine blocks are low quality, you are wrong. engines still last for years on salt water, maybe the ones you seen with corrosion may not have had their anodes maintained.

 

From the General Motors Powertrain website:

GM Powertrain has designed a number of important features into its marine engines, such as corrosion-resistant alloys, engine oil sealing system, marine-specific camshaft designs for some applications, and cooling systems that are compatible with both salt and fresh water environments.

Because GM Powertrain knows the tremendous demand put on engines in the marine environment, GM marine engines are "tested tough" by being run at extensive wide-open throttle conditions, under load, when subject to the Marine GED Test Schedule (Global Engine Durability).

I don't know if the metal in current GM marine engines cylinder blocks is the same as current GM engines for installation in vehicles. I also don't know if the metal composition of the marine engine blocks and/or vehicle engine blocks has changed over the years.

Can anyone who does know share the sources of their information?

 

That's what I remember reading forty years ago though I'm not sure the problem is the salt or some of the other compounds in seawater.

Sugar is not salt and the chemistry is different.

 

A reasonable guess but only a guess.

 

the question was /Vortec 4.3 cracked block ... automotive swap ,so it can be done.its up to him will he buy automotiv for few100 usd or marine block for 1k usd is the only question..if im in ur place in usa i would go with automotiv block

 

Salt begins to deposit in a engine if the temp is above 50 celsius and chemical corrosion rate is a square function of temperature... Raw cooling of a small engine is a non-sense; the salt will eat any iron alloy, nickel or not nickel unless you're above the 10%. A too cool engine (70 celsius) is inefficient and dirty. An engine must run as adiabatic as possible, ie as hot as possible. On gas engines is around 90-92 celsius.

About corrosion have a look inside a lot of outboards used in tropical waters and you'll be convinced that salt water has no place inside a small engine. The Hondas die here in less than 2 years because of corrosion.

So the best service to make to an engine is to install a fresh water cooling ie a true cooling with heat exchanger and antifreeze. If working 1000 hours year you'll get back your investment in less than 3 months in gas consumption. On a 5.7 L 320 HP the specific consumption goes from 230 gr./HP/hour to 200-205 gr./HP/hour, that's a lot.

The justifications of the difference of price between the 4.3 car and 4.3 marine is advertisement bla-bla. The car block works perfectly. We do that here all the time. Just paint it black with a good and glossy polyurethane enamel.

 

Thank you for chiming in Ilan.

The only way to find out what a cast iron block is made of, you need a hammer and chop off a piece, not cut it off. If the break surface is gray, you have ASTM A48; if it is silvery or white, the material is an iron alloy with high nickel, tungsten, copper content.

I've owned, maintained and discarded several Merc. 3.0LX engines and I know exactly what the broken material looks like. One of the engines is still in function as a dead weight for my aft mooring line. It performs excellently there, sunken deep in the mud.

The Volvo B20/B30 blocks Brendan mentioned may very well be different. Volvo keeps surprising me with constructions and quality materials, they really do their utmost to make long lasting products.

 

Not all gray appearing cast iron is ASTM A48. There are numerous cast iron compositions, some of which are proprietary, with varying amounts of alloying elements.

 

There are many irons alloys. White iron is generally carbide kind, gray iron graphite kind. Plus the different heat treatments.
But do not worry: iron used in blocks are rather simple as the first asked quality is "castability" (so a high content of silicon at the expense of brittleness),low cost and machinability.
No engine maker would use a high alloyed (with expensive metals as nickel or chromium) iron for engine blocks: simply too expensive. If nickel is used it would be in very low percentages.
Better and cheaper to go to aluminium alloys as most of the European and Japanese engine makers do.
So the iron rusts steadily in salt water, and combined with aluminium elements as heads, water pumps and others make a nice battery with a splendid electrolytic corrosion of all the alu parts. In brief bad engineering. But people are used to.
The 3.0L is just good as anchor. Not reliable and impossible to rebuild. The 4.3L has not a great track of reliable marine working engine.

I almost forgot: it's very possible to repair a crack in a iron block engine. There are several methods (mechanical and welding) but that needs a good knowledge of the technique.

 

The part numbers on a marine and an automotive block are different.