2002 Mercruiser 3.0 - No Oil? Engine Swap?

Hatch19

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Apr 18, 2025
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3
Hey guys - Two part question..

#1 - I recently acquired a 2002 Bayline with a 3.0 Merc that hasn't ran in 2 years. It does have a crack on the port side of the block (unknown if overheated or not winterized). I Drained the oil out of it and did get some water but it was not milky looking. Put 5 Qts of oil into the fill and nothing shows on the dip stick and there are not visible external leaks anywhere (I have not attempted to run it) I'm at a loss.... any suggestions?

#2 - I'm looking at just swapping the motor out with a known running one. Will a 1997 Merc 3.0 be a direct drop in fit? Only difference I can see in my motor and the new motor is where the shift cables mount up (starboard side vs on top of the rocker cover)

Any input is appreciated!
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,777
Hey guys - Two part question..

#1 - I recently acquired a 2002 Bayline with a 3.0 Merc that hasn't ran in 2 years. It does have a crack on the port side of the block (unknown if overheated or not winterized). I Drained the oil out of it and did get some water but it was not milky looking. Put 5 Qts of oil into the fill and nothing shows on the dip stick and there are not visible external leaks anywhere (I have not attempted to run it) I'm at a loss.... any suggestions?

#2 - I'm looking at just swapping the motor out with a known running one. Will a 1997 Merc 3.0 be a direct drop in fit? Only difference I can see in my motor and the new motor is where the shift cables mount up (starboard side vs on top of the rocker cover)

Any input is appreciated!
#1 - block wouldnt crack like that from over heat only from not winterizing - also need to check if manifold is cracked as well.

it is worth starting it on the hose and seeing if you get water into the oil . Sometimes will just crack externally and people slap JB weld on it and call it good.

1997 will be a drop in. Especially if you have two engines worth of acessories etc.

In all likely hood the block is toast, would look the boat over drive as likely it had no maintenance. Fuel may be contaminated as well.
 

Hatch19

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Apr 18, 2025
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3
#1 - block wouldnt crack like that from over heat only from not winterizing - also need to check if manifold is cracked as well.

it is worth starting it on the hose and seeing if you get water into the oil . Sometimes will just crack externally and people slap JB weld on it and call it good.

1997 will be a drop in. Especially if you have two engines worth of acessories etc.

In all likely hood the block is toast, would look the boat over drive as likely it had no maintenance. Fuel may be contaminated as well.
Scott - Thanks, the "new to me" motor is a complete set up so I'm leaning towards just a swap... time troubleshooting issue motor vs swapping a working one.

it is worth starting it on the hose and seeing if you get water into the oil . Sometimes will just crack externally and people slap JB weld on it and call it good. I have read that and that was my initial plan but... after adding oil I still have none in the pan.. confirmed by attempting to drain the oil again... I'm hesitant to run a motor that I cannot verify it has oil.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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50,313
the dividing line on the block and heads is 1990. so anything from 1970 something to 1990 will swap within that time period, and anything post 1991 to when GM stopped making the 3.0 will swap in. the only odd one is the EFI version of the motor.
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,777
Scott - Thanks, the "new to me" motor is a complete set up so I'm leaning towards just a swap... time troubleshooting issue motor vs swapping a working one.

it is worth starting it on the hose and seeing if you get water into the oil . Sometimes will just crack externally and people slap JB weld on it and call it good. I have read that and that was my initial plan but... after adding oil I still have none in the pan.. confirmed by attempting to drain the oil again... I'm hesitant to run a motor that I cannot verify it has oil.
Was thinking the dipstick was broken or wrong one ... You put 5 qts in the engine (its a 4 qt motor) and there is nothing in the pan? You pulled the oil pan drain plug and there is no oil? Not sure where it would go unless it leaked out somewhere ??

Cant conceive a situation where the head wad cracked such that it filled the cylinders or block was so cracked it filled the cooling jacket- dont think on the lifter side there is a jacket behind the lifters/pushrods.

if the cost of the other engine doesnt bother you and it is actually a good engine (compression and oil pressure) may be a better bet
 

Hatch19

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Apr 18, 2025
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3
Was thinking the dipstick was broken or wrong one ... You put 5 qts in the engine (its a 4 qt motor) and there is nothing in the pan? You pulled the oil pan drain plug and there is no oil? Not sure where it would go unless it leaked out somewhere ??

Cant conceive a situation where the head wad cracked such that it filled the cylinders or block was so cracked it filled the cooling jacket- dont think on the lifter side there is a jacket behind the lifters/pushrods.

if the cost of the other engine doesnt bother you and it is actually a good engine (compression and oil pressure) may be a better bet
I had the same thought about the dipstick so I straightened out a coat hanger and pushed it all the way in, still nada.

Compression on the replacement motor is ~170psi.

The motor is already out of the boat, is there a simple way to check oil pressure?
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,777
I had the same thought about the dipstick so I straightened out a coat hanger and pushed it all the way in, still nada.

Compression on the replacement motor is ~170psi.

The motor is already out of the boat, is there a simple way to check oil pressure?
Then WTF did it go... I mean I haven't started drinking yet.

take out the sender and hook up a mechanical gauge ($25 at autoparts store). When hot if it has 10 psi for every 1000 rpm of engine speed your bearing clearances are good.

Very easy to run and engine on the ground
 
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