1985 3.0 liter, 140 hp Merc (Larson)

[ddbyrd3]

I am working on my friends boat (3.0 liter Merc) It has been sitting for 8 years. Believe it or not, after a few preliminary checks, verifying power, fuel, ect, she fired right up, and even idoled nicely. Unfortunitly when we shut her off I noticed water in the oil. We drained it, changed it, and refired the motor. I let if run for about 15 minutes or so, volts, oil pressure, water temp all looked good. Shut it off, pulled the dip stick, sure enough the now milky oil was a 1/2" over the full line. I dont know the history of this boat, and it is looking like a head gasket, but I was curious if these motors were notorious for head and block cracking?

I will do a compression check tonight and confirm. One more thing, as the motor was running, you could see milky oil coming out behind the starter and flex plate area. Any idea what may be causing that????

 

[Silvertip]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

Blocks and heads crack on any I/O if it is severely overheat or wasn't properly winterized (assuming the temps actually get below 32F where the boat was stored). So the answer to the question about is this common on the 3.0 -- NO!

 

[totx]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

I will do a compression check tonight and confirm. One more thing, as the motor was running, you could see milky oil coming out behind the starter and flex plate area. Any idea what may be causing that????

Rear seal on the engine.

Did you check the oil before you fired it?

Water intrusion:

1. Manifold
2. Riser
3. Mating suface between manifold and riser
4. Cylinder head
5. Block
6. Cylinder head gasket

 

[ddbyrd3]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

Yes I checked the oil before firing it. It had been sitting for 8 years. It had a slight cream color. I drained the crankcase the best I could and changed the filter. Once I got it running I checked the oil and is was real creamy white.

Last night I changed the oil again (after warming the oil) and ran it, the cream color appears to be going away, and the crankcase didnt fill with water. I ran it for 20 minutes or so, the the oil level never went above full.

I did a compression check on the motor and this is what I got.

Front cylinder: 185, 185, 185, 165.

It appears the rear main seal is leaking. How else can I check for a bad headgasket, or at least try and determine how the water got in the oil?

 

[greasemonkey1985]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

not too sure the conditions of the storage, but possibility of condensation build up inside the engine during 8 years of storage causing water to sit in different low areas inside the engine, as you were running it for the first bit the oil would mix with the water and bring it down to the pan.

 

[ddbyrd3]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

I was thinking that same thing. it had the engine cover on it, but nothing else. I did notice last night that the cup holders were missing from the enging cover, and the PCV valve sit darn close to one of those holes. It dont rain much here in Calif. but the temp cycles may cause condinsation to build. I am not sure....

She runs real good though. I have done nothing other than drain the oil and fuel, clean and gap the points and she fired up on the 4th ot 5th try. all the gauges look good, just the oil pouring out between the flex plate cover and starter motor.

 

[ddbyrd3]

Re: 1985 3.0 liter, 140 hp Merc (Larson)

I put fresh oil in this thing again, and let it run for quite a while.... However it is obvious the rear main seal is leaking REAL bad. Once I pull the motor, how difficult is it to replace the seal?

Is it a 1 peice or 2 peice? Either way I assume the oil pan will have to come off.... Is that correct? Am I missing anything???