1995 Mercruiser 5.7l block replaced with truck block difference

thormx11

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Hello, I bought a boat of my father this past week. The boat had a 1995 Mercrusier 5.7l engine, and he never winterized it and the block cracked. Long story short, we had a 5.7l block out of a 90's model truck laying around. Everything looked to be the same at the time. So he took both engines to a local machine shop to change the blocks and freshen the new motor up. Now I am working on installing the engine in the boat, but I noticed a difference in the water pump. The new (truck) block doesnt seem to have a third hole on the left side where the water pump mounts. There is a port of some sort going through the water pump that looks like it should go through the engine. Any idea where this port goes and if it will matter? After looking online, some marine blocks seem to have it and some don't.

It is the bottom hole on the left side where the water pump mounts.
 

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Scott Danforth

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Block and heads same. Marine engines get brass core plugs, marine head gaskets and marine water circulation pump.

Not sure if the extra threaded hole is in the waterjacket. If it is, put a set screw in the hole with loc-tite
 

thormx11

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Sorry, I should have added a pic of the water pump as well. That bottom hole in the block is matched by a port out of the water pump. My new water pump has the port, but it will not go into the block.
 

thormx11

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I could seal the port off from the water pump with no problem. I am just concerned with where that hole goes into the block. From what I can tell, it seems like it would go up into the head. I'm not sure if sealing it off will cause a problem
 

Bondo

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There is a port of some sort going through the water pump that looks like it should go through the engine. Any idea where this port goes and if it will matter?

Ayuh,..... Are ya usin' the waterpump off the truck, or the boat's original,..??
It's just another passage, from one to the other, probably common to each other, on 1 side or the other,...
we had a 5.7l block out of a 90's model truck laying around.

1990, What,..?? Pre- '96,..?? post- '96,..??
 

thormx11

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Ayuh,..... Are ya usin' the waterpump off the truck, or the boat's original,..??
It's just another passage, from one to the other, probably common to each other, on 1 side or the other,...


1990, What,..?? Pre- '96,..?? post- '96,..??



Neither. the pump off the marine engine was locked up. I matched the water pump up at a local parts store, off a 1965 327 engine. It has the same port as the original marine water pump.

I am going to try to run the engine and see if there are any problems. I sealed the port off on the pump.
 

thormx11

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Ayuh,..... Are ya usin' the waterpump off the truck, or the boat's original,..??
It's just another passage, from one to the other, probably common to each other, on 1 side or the other,...


1990, What,..?? Pre- '96,..?? post- '96,..??



And i am not 100% sure on the year, I want to say 1991. The engine rebuild/swap has been ongoing for 3-4 years now.
 

Rick Stephens

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Unless you have a closed cooling system, you will need to run a marine water pump. Amazing how fast you will rust out an automotive water pump that has metallurgy designed for antifreeze.
 

Bondo

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Ayuh,.... Ditto,..^^^^^ Get the water pump that's for the take-out Marine motor,....
 

thormx11

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Thanks for the replies. I will definitely pick up a new marine water pump for the boat. I already have the automotive water pump on the boat and will use it to run the boat on muffs and work the kinks out of the boat (there should be plenty after sitting 5 years) but I will replace it before I put it in the water and start using it heavily.

My biggest concern though was the port in the engine. My new engine doesnt have the port going into it like the marine engine did. I don't want to burn the engine up.
 

Scott Danforth

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Neither. the pump off the marine engine was locked up. I matched the water pump up at a local parts store, off a 1965 327 engine. It has the same port as the original marine water pump.

I am going to try to run the engine and see if there are any problems. I sealed the port off on the pump.

you need a marine water pump. brass impeller and stainless cover plate.

make sure you have brass or stainless core plugs and make sure you have marine head gaskets.
 

thormx11

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I know the engine has brass freeze plugs and a marine gasket kit.
 

Scott Danforth

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they are core plugs (or welsh plugs), not freeze plugs. their sole purpose is to get the core sand out of the block during the casting process.
 

Bondo

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My biggest concern though was the port in the engine. My new engine doesnt have the port going into it like the marine engine did. I don't want to burn the engine up.

Ayuh,.... I ain't gone 'n found a block to look yet, but If I remember right, that's just another hole, like the 1 above it, goin' to the same place,....

I believe the extra hole has to do with ventin' the system as it fills with water,....
Chevys have had 'em, since the beginin',....
Maybe some bean counter decided the cost was unnecessary, donno,...
 

icwingman

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Just some info: Boat V8 motors are 4 bolt mains on the bearings. This is used because the rpm is constant most of the time. Truck motors are usually 4 bolt mains also. You might have to hit a few junk yards for that water pump issue. Good LUCK.
 

Scott Danforth

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Just some info: Boat V8 motors are 4 bolt mains on the bearings. This is used because the rpm is constant most of the time. Truck motors are usually 4 bolt mains also. You might have to hit a few junk yards for that water pump issue. Good LUCK.

only some of the motors were 4-bolt. most are 2-bolt. same with trucks. only the heavy duty trucks get 4-bolt.
 

dan t.

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The hole you are missing is the coolant bypass so coolant will circulate through the block until the thermostat opens, The block you are using must be from a 96-98 vortec, they had a different water pump,
 
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