3.0L 140hp mercury engine 1985

Knot_rite15

Recruit
Joined
Sep 29, 2016
Messages
2
Hey all I have a 1985 StarCraft islander
It has a 3.0l 140hp murcruser engine. My friend sold it to me I knew it had engine issues. He mechanic says it's a head gasket. No water in the oil but they did compression test water shot out the one spark plug hole . They had to limp it in but it was running . How do I figure this out or what do I have to do to get this thing running again. Was going to put plugs in and hook up hose and run it and see what happens.
Or what you guys think i should do, and what tell tail signs of the head gasket being bad before pulling head off. Again it's a 3.0L 140hp murcruser 4cylinder I'm new to this type of engine used to outboard mercury engine so any help would be greatly appreciated.
Thank you again
Matt owner of knot_rite and hell on reels
 

tlewis1

Petty Officer 2nd Class
Joined
Oct 9, 2012
Messages
112
Well a compression test and leak down test sound like they are in order. That will tell you whether or not a head gasket is required. Those would be the first two thing I try. No need to try and run the engine up without performing those two things, may just cause more damage.
 

bman440440

Petty Officer 1st Class
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Apr 4, 2011
Messages
266
here is my 2c... if water came out threw the spark plug holes it can only come from 2 places.... 1st is head gasket or cracked head... 2nd is exhaust manifold/riser... either way at the least the head needs to come of and sent in to be checked and or rebuilt... then are you SURE that there is no water in the oil?? if there ends up being water in the oil then it is best to have the engine gone threw and freshened up... now on to the manifold/riser... if it's more than 3 years old and been used in salt water its prob a good idea and get new ones even if it was not the cause of your water in engine problems... those 3.0 where used in a lot of ford cars and any quality machine shop can go threw it at a minimal cost... just make sure that when they reassemble it to use a marine head gasket and brass freeze plugs... I did my 4.3 v6 with new bearings, rings and complete valve job on both heads for $750 out the door for the assembled long block... so I would think you would be around $600 for the piece of mind knowing that your motor is sound and ready to rumble for years to come!!... so like I said that's my 2c and you can take it for what its worth
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
3.0 was never an automotive engine. Only industrial and boats. Makes them a little more expensive to rebuild.

First thing compression test. Leakdown never hurts. Run on muffs for sure. Long as no cylinder has water in it you won't be likely to hurt it running it for a test.
 

Knot_rite15

Recruit
Joined
Sep 29, 2016
Messages
2
Thanks guys on the info I just got new plugs for the engine and I will be running the hose tomorrow. And I will be checking things out and taking to a mechanic after that but thanks again
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,306
find out why there is water in the cylinder. a compression test and leak down test will indicate this. if everything is good, my guess is the manifold and riser gasket or the manifold has long since deteriorated from rust.

how long has the motor been sitting with water in the cylinders. if more than a day or two, the cylinders have started to rust. get the motor running ASAP

the 3.0 is a 4.0" bore and a 3.6" stroke the good news is they use GM 350 pistons and rods so when buying pistons, buy a set of 8, throw away 4 and your cheaper off than buying a set of 4.
 

airshot

Rear Admiral
Joined
Jul 22, 2008
Messages
4,219
Why not just pull the manifold and head then you can see for sure where your problems might be. I just did my 3.0 this past spring....head resurfaced, new springs and valves ground, manifold gone thru and all reassembled, runs like new! Just under 400 bucks all total.
 
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