Merc 4.3 problem

srt8mag

srt8mag

Member
Jan 2, 2008
146
Mt. Pleasant, SC
Boat Info
280 Sundancer SOLD
Engines
4.3's w/ A1's
Hey Guys,
Starboard side 4.3 was losing oil pressure on my run home yesterday. Usually right around 50psi when cruising. It has 177 hours on it. Watched psi drop down to around 36psi and smartcraft alarm sounded and check engine appeared. It was a process of about 20 minutes when the pressure fell slowly from high 40's to 36psi. No noises, no power loss, no smoke. Got back to the dock and checked the engine and found a milky white oil on the inside of the filler cap. Dipstick oil seems good, with no milky white color. Thoughts?
 
Milky white is an indication of water. Could be head gasket failure.

How many hours are on this oil change? Are you familiar with the boat - is it new to you?

Have the oil dropped and inspected.
 
Any water that gets in the oil will end up in the filler neck as condensation as that is the highest part of the crank case.
 
Last year when my port 4.3 died it was a cracked head. When i checked the dipstick it showed oil and not milky white, it was however showing it was over the fill line. Once i started to change the oil i saw the milk...
 
Y Knot said:
Last year when my port 4.3 died it was a cracked head. When i checked the dipstick it showed oil and not milky white, it was however showing it was over the fill line. Once i started to change the oil i saw the milk...
Click to expand...


UGH!!!! I'm hoping for the best on this one. Not looking good though. I hope it's just excess condensation from the boat sitting for 2.5 weeks on my lift with no use. My plan is to change the oil/filter and try it out. I'll post the outcome when I do.
 
Issue seems to be back. I began to lose pressure again after 10 hrs of run time on new oil. I also noticed a little condensation on the enging oil fill cap. I changed the oil and filter, (which looked fine not milky white) and the pressure was back to normal while running for about half an hour. When I returned to the dock I checked under the cap again and noticed a few tiny water droplets.
Could it be a bad seal on the dipstick, or fill cap which lets in a bit of moisture as the engine is running? I would think that if it were a head gasket there would be more moisture?
 
How much moisture are we talking about under the cap - can you post a pic?
 
PMC said:
How much moisture are we talking about under the cap - can you post a pic?
Click to expand...

I left the boat at my parents dock yesterday but I'm headed there tomorrow to bring her back to my house. It's about a 2 hour run at mostly cruising speed so I'll report back and take some pictures too.
 
No water on the oil fill cap this morning. Ran great at about 3550 rpm for 2 hrs. Perfect oil pressure and no water on the cap after a cool down. It's a conundrum...
 
Lost oil pressure again yesterday. Water on filler cap again. Got home and put her up on my lift and discovered the exhaust bellow is detached from the drive! Looks loike I'll have to haul out and fix ASAP. Anyone ever do the bellows as a DIY?
 
Easy to replace, but not your problem. You can run without an exhaust bellows if you really wanted to, just going to be louder.

I'd do a compression test, that will tell you everything you need to know. If you dont feel comfortable doing it then bring it to a marine mechanic.

Not to scare you by any means but the 4.3l's have a very small coolant passage in the lifter valleys and are very prone to cracking wether it be lack of winterization or overheating. This is why i recommend a compression test.

I've replaced 3 this year alone....all cracks in the same spot.
 
Last edited:
SR Tech said:
Easy to replace, but not your problem. You can run without an exhaust bellows if you really wanted to, just going to be louder.

I'd do a compression test, that will tell you everything you need to know. If you dont feel comfortable doing it then bring it to a marine mechanic.

Not to scare you by any means but the 4.3l's have a very small coolant passage in the lifter valleys and are very prone to cracking wether it be lack of winterization or overheating. This is why i recommend a compression test.

I've replaced 3 this year alone....all cracks in the same spot.
Click to expand...

Thanks SR Tech. My buddy (BeachcomberSC) told me the same thing about the exhaust bellow. His have been detached for 3 yrs with no issue. When you say you replaced 3 what do you mean? 3 what? 3 entire engines?
 
Yes, 3 short blocks. After all said and done most of them averaged out at $2500 including the block and my labor.

2 due to lack of winterization
1 overheated severly

But you dont want to hear that :grin:

The only way to really tell is, if you keep getting water in the oil after changes. Or you physically take off the intake manifold and have a peek.
 
Last edited:
SR TECH= Would he have perform a full leak down test to truly know? Or just a normal compression test?

How much water would it take to produce foaming in the oil to allow a drop in pressure?
 
"The only way to really tell is, if you keep getting water in the oil after changes. Or you physically take off the intake manifold and have a peek."

Unfortunatly because the lifter valleys do not coencide with the combustion chamber, a leak down or compression test will not find the problem. Over time after the oil mixes with the water well enough and starts eating at the valve seals or piston rings, it will then show on a compression/leak down test.

The thing with the pressure is that it will drop it at first with the 'milk' being produced, but as water keeps entering it will being to build pressure due to high volume, which inturn will start to blow out seals and gaskets i.e. intake
 
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