4.3L Mercruiser Milkshake

[Lukey220]

Hey everyone, I bought a boat with a 4.3l mercruiser and I have been fixing it up. Finally got to starting it today on muffs and… milkshake oil started spraying out of the breathers on the top of the valve covers. Checked dipstick and oil level was high and also milkshaked… really hoping this isn’t a cracked block but deep down feel like it is.

As I was fixing it up I noticed the engine must have been overheated as the exhaust bellow, shift cable, and hydraulic lines were melted. Is there anything in the risers/exhaust manifolds that could cause this from being overheated, or is generally a milkshake spray mess from a cracked block?

Thanks everyone!

 

[Silvertip]

Blown head gasket due to overheat is another cause.

 

[Lou C]

The milkshake could be from blown head gaskets due to an overheat; you can air pressure the cooling passages to see if they hold pressure (15 psi). I had an overheat on mine then the head gaskets blew approx 3 seasons later. Wound up taking it apart & replaced the head gaskets & heads (cracked) but the block was fine and it’s still running fine 5 years later. I’m not saying blocks never crack due to overheats but I think heads cracking is a lot more common.

 

[Rick Stephens]

Fair warning, most blown head gaskets don't fill the block with water in a short run on muffs. More likely a cracked block. As noted, doing a cooling system pressure test is the way to get an idea. Also a compression test.

 

[Scott Danforth]

when a boat motor stops getting cooling water from the $15 impeller that someone didnt change, the exhaust temp goes from 200 F to 1100F in a matter of seconds

the milkshake could be from that severe overheat

regarding your block/heads. drain the cooling system and pressure test the cooling water jacket. it should hold 15 psi forever

do a compression test. your numbers should be about 150 psi

do a leak down test.

 

[Lukey220]

Awesome thanks for the replies everyone. I will start on it tomorrow. What’s crazy to me is how fast it fills. It fills the crankcase to the top and flies out the valve breather without a minute of being running , and today when I opened the water drain plugs they are bone dry like water isn’t even flowing through the cooling system, just straight into the block.

I’ll let you guys know what I find.

 

[Lou C]

Almost sounds like the water wasn’t drained & it froze over winter

 

[Lukey220]

Almost sounds like the water wasn’t drained & it froze over winter

Could have! I’ll find out when I dig in , previous owner said it sat for 2-3 years because it needed fuel pump but that could have been a cover story for a cracked block.. time will tell.

 

[tank1949]

Could have! I’ll find out when I dig in , previous owner said it sat for 2-3 years because it needed fuel pump but that could have been a cover story for a cracked block.. time will tell.

time to look for another motor. Sorry...

 

[Lou C]

Look at as an opportunity to upgrade to a late model 4.3 with Vortec heads, 4 bbl carb & balance shaft.
BTW one thing I love about this engine is how economical it is with the 4 bbl Quadrajet carb. While the 4.3 is a bit underpowered in my heavy 20’ bow rider given the high cost of fuel now ($5.99 a gallon at our gas dock) it’s not a bad compromise now. I compensate by using a low pitch prop (15.5x15) and give up some top speed.

 

[Lukey220]

Just another quick question for anyone who knows.. will a Mercruiser 350 bolt up in place of my 4.3? Both late 80’s Motors but the 350 is rebuilt with receipts and looks real clean for a decent deal.

 

[Lukey220]

Just another quick question for anyone who knows.. will a Mercruiser 350 bolt up in place of my 4.3? Both late 80’s Motors but the 350 is rebuilt with receipts and looks real clean for a decent deal.

 

[Scott Danforth]

Just another quick question for anyone who knows.. will a Mercruiser 350 bolt up in place of my 4.3? Both late 80’s Motors but the 350 is rebuilt with receipts and looks real clean for a decent deal.

It will bolt to the flywheel housing

Was the motor built as a marine motor?

You will most likely need to fiberglass in new mounts

Do you have 4.25" extra in the bilge

You will need new exhaust manifolds, a new marine distributor

 

[dubs283]

You will need new exhaust manifolds, a new marine distributor

And ignition system. Guessing the 4.3 is thunderbolt, v-6 module won't cooperate with a v-8

 

[Lukey220]

It will bolt to the flywheel housing

Was the motor built as a marine motor?

You will most likely need to fiberglass in new mounts

Do you have 4.25" extra in the bilge

You will need new exhaust manifolds, a new marine distributor

Yes it was a marine engine that got rebuilt. It includes new exhaust manifolds/risers , wiring harness and thermostat housing.

I definitely have the extra bilge space as I move the fuel tank forward about 8” when redoing my stringers and floor.

Thanks for the answer!

 

[Rick Stephens]

Be some work and significant added expense. If you like doing fiberglass fab work the extension on the motor mounts is easy enough. Will be interesting prop'ing the 1.84 4.3L drive to a 5.7L motor.

 

[Lukey220]

Thanks for the reply Rick, What added expenses do you figure? I know I’ll need a new distributor as Scott said, it includes the exhaust manifolds/risers. Anything else I’m missing that won’t be reusable off my 4.3?

 

[dubs283]

Anything else I’m missing that won’t be reusable off my 4.3?

Post # 14

FYI, if indeed a thunderbolt ignition the distributor will be okay. You need a v-8 cap and rotor and as I mentioned earlier a v-8 module

 

[Lukey220]

Post # 14

Oh okay totally missed your post dubs. Thanks a lot!

 

[Lukey220]

Post # 14

FYI, if indeed a thunderbolt ignition the distributor will be okay. You need a v-8 cap and rotor and as I mentioned earlier a v-8 module

I asked him if it included a module and this was his response…

It had a Mallory points and condenser distributor that I swapped the points out for a Pertronix Electronics ignition kit in. Way more reliable than any Thunderbolt module and if it were ever to fail I can put the points back in and be boating in 10 minutes. I’ll throw in the distributor at no charge.

Sorry for all the questions haha, this whole project has been a big learning curve for me. Would this mean I have everything needed for the ignition side then?