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Volvo Penta 5.7 1996 TBI Low compression and steam out of crank breathers

E

EugeneCan

New member
Hello everyone! Sorry for starting a new tread.. I'm sure it has been discussed here more than a dozen times..

I just bought this boat and seller said "something wrong with starter" so I never heard it running before purchasing.
After fixing wiring and then new fuel pump it runs, but first run yesterday was very rough with some ticking especially as rpms brought up and also noticed steam coming out of both sides crankcase vents..

Today performed compression test (spark plugs on starboard side had some rust) and two adjacent cylinders (middle starboard) had 75 and 120 respectively, while all others between 160-170.
I sprayed some penetrating fluid (couldnt get any hose to put gear oil) and compression raised to about 85 for one test and droped to 75 again after.
Now the question is if its a leaking elbow gasket caused the valves on cylinders 2 and 3 to be stuck, why am I getting steam out of both crank vents? I imagine it would be another problem?

I haven't pulled anything apart. Just going through what could cause all these.
Thank you.
 
Welcome
Have heard folks saying there is a problem with the starter to hide known problems with the motor many times

Steam, low compression, rust all lead back to blown head gasket or a crack.
 
Because the rust in those cylinders, may have corroded the cyl walls and now the rings won't seal hence blow-by. If you have one of those endoscope inspection cameras you can check it through the spark plug hole.
If you get water in the cylinders of a marine engine, you need to deal with it RIGHT AWAY. This includes bad elbow/manifold gaskets, and blown head gaskets. I had the latter about 10 years ago, and managed to preserve the engine by draining out all the water, and spraying fogging oil in the cyls, cranking the engine over, fogging again. When I took it apart a few months later the cyl walls looked fine. All engines will have blow by but with low compression you have, those cyl heads need to come off to see if it can be saved. It's a shame, especially if it was from something as simple as a leaky exhaust manifold gasket.

4.3 starboard cyl head removal.jpg

the front cyl on this side is the one that had water (salt water) in it not enough to hydrolock but definitely some water, this is when I took it apart in Feb 2017, I pickled with fogging oil in the fall of 2016, and you can see the cyl walls are not rusted.
It got new head gaskets, reman cyl heads, and a 2 piece (from the old OMC batwings) exhaust conversion...
4.3 with new exhaust system.png

At the end of each season I use an endoscope camera to check for leaks in the exhaust system, I can remove a pipe plug fitting on the top of the exhaust elbow and get a pic of the inside....
exhaust staboard side.jpg

this is what a good one looks like....sometimes you will see little rust pits from condensation but you should not see rust in the bottom of the manifold, that is a sign of water for sure getting in.
OMC/Volvo exhaust is a "cold manifold" system and you can see condensation on the port side especially because it runs a bit cooler than the starboard side. But that's normal for them. The manifolds will run between 100-110*F at idle, if you haven't gotten the boat up on plane. Mercrusier switched to a "hot manifold" system to eliminate condensation from running at idle speed by keeping the manifold temp above 120* F which will burn off condensation. OMC/Volvo never changed theirs so there is that but you must check for water leaking in which is a different problem altogether.
 
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Thank you @louc. This is really comprehensive explanation.
I dont know why I didnt think of stuck piston rings🤷
I've had 3.7L Mercs, Volvo AQ131 4 cyl and 351 on ski boat before but somehow got away from doing any major work. I guess its not the case now.

Interesting they replaced port side manifold- its a fresh Sierra with parts number, but starboard looks like been there for long while with bolts rusted out. Should've done both..
 
Are Sierra or Chinese manifolds any good? I would prefer to do these on budget if possible. We didnt plan for extensive parts list unfortunately.

Im gonna use this boat maybe 20-30 hours a year on fresh water only.
 
I used Barr American made manifolds when I did my conversion 9 years ago. Still fine no leaks inside.
 
Just an update.. I've soaked all the cylinders with deep creep for 5-6 days and now good cylinders have higher compression (175-180) and two bad ones dropped to around 20 and with some oil to 50.
Is it because carbon was actually sealing it?🤔 Any other guesses?
 
*Got it started and ran for about 10 min. Retested compression and 150 in both cylinders 🤙 I guess oil and carbon was washed out along with all the rust and thats why I had no compression.

Was running rough after got warmed up, I assume cause manifold leaks water into starboard side.
I got brand new manifold so gonna replace it and see if it solves it.
 
Just an update here..
Got a new manifold and new risers installed.
Engine runs rough at idle with hissing sound from throttle body and sometimes when RPMs brought up it starts knocking and stalls. Also fuel priming bowl gets very soft after a bit of running.
Where do I test fuel pressure? I only have test port before the high pressure pump. Low pressure just was replaced.
 
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