Mercruiser 5.0L block swap

[105mich]

Hi I have a 1989 mercruiser 5.0L, unfortunately the block is cracked. I'm very good mechanically and have the tools so i am going to get a new block and rebuild the engine. My question is, what mercruiser engine years can I take blocks from that will work in my 89? Or did they use the same block for all mercruiser gm v8 engines?

 

[Bondo]

Ayuh,.... Welcome Aboard,.... Mercruiser has used the same blocks that Chevy was puttin' into pickups in any particular year,....

So,... The Best match would be a Chvy 5.0l block from '86, 'n up,....

The heads changed in '96, so yer intake won't fit a '96, 'n up vortec headed block,...

Personally, I'd go for a current production 350, with vortec heads, then buy a matchin' intake manifold,...

The bolt holes for everything else is the same,....

 

[105mich]

Ok so I could take the block from an 88 mercruiser 898, since they are both 305? I just happen to have access to that one

 

[Rick Stephens]

You say that as if you don't have 'access' to a few hundred thousand Chevy 350 engines that were not once put in a boat. I'd rather have a used truck motor than a used boat motor, seeing as how they are the same thing. Typical boat motor has a tougher life than the typical truck motor.

 

[Lou C]

At least the truck motor has had antifreeze going through it instead of raw water, but if you go that route, unless you use closed cooling you will need to use the marine head gaskets and core plugs. Even in fresh water.....If the block/heads of the old engine were cracked (freeze damage?) don't forget you also have to replace the exhaust system as well, if it was not drained.

 

[105mich]

Ok thanks alot, I am going to go with a 350 block and buy the intake manifold. Will all the rest of my working parts from my 5.0 work with the 350 long block?

 

[Rick Stephens]

The blocks are the same. Where the potential issue comes in is front accessories. If you get a newer motor it probably comes with serpentine belt pulleys on the harmonic balancer. Your 89 has v-belts. You have to swap over t least the alternator and water pump. The older harmonic balancer won't swap to a newer harmonic balancer block. You can probably get a v-belt pulley to bolt onto the balancer and even the alternator, but will have to search these out or purchase a complete balancer. Also I do not believe the water pump is the same between pre-balance shaft blocks and balance shaft blocks. If you try and use an automotive water pump on a fresh water cooled marine engine it will rust out in no time. Auto pumps are made to run in antifreeze which also prevents rusting.

In my opinion, it is worth it to go with a newer Vortec engine. Probably cheaper to find as well, since they are common as dirt. But there are a few headaches. There are also things that are dead simple - exhaust will direct swap.

 

[105mich]

I decided I am going to patch the hole and see what happens with it, if i survives till fall then great if not then ill rebuild. Might as well try to get a season out of it and rebuild during winter

 

[Maclin]

Usually a V8 block with freeze damage has internal cracks in the water passages, these are the problem and why a new block is the only answer most times. So I guess the question from me now is, how was it determined that the block is cracked? If just an external visual check found them, then there may also be deeper problems, just sayin'. If you decide to patch an external crack and go boating, stay close to the ramp for a while as the engine comes up to temp and load is applied. That is when any internal cracks will open up and start spewing water into the crankcase. Good luck!

 

[105mich]

I know its cracked because i ran it and there was water coming from a large crack which is now a 4x4 hole in the block

 

[Rick Stephens]

I know its cracked because i ran it and there was water coming from a large crack which is now a 4x4 hole in the block

At least it isn't a hidden problem. Dang, never seen a 4 x 4 hole.