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1997 350 TB crankcase moisture venting...?

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Blackfin27

Contributing Member
Back on the board for some help....troubleshoot this please:

Twins Hours 770, new risers 2 years ago, ignition coils, distributor kits. Had a tech with solid reputation do some evaluating for warm port engine, but not overheating. This engine runs well generally. Determined on test run that the "port engine crankcase is venting moisture". The recovery tank hose had a hole and replaced. Added coolant.

Can you dummy this condition down please....whats coming my way eventually...? Same engine has some lower compression readings on #3,4,5. Related?

I know a repower or major overhaul is coming. The tech said he couldnt go any further without a tear down so Im hoping to limp along til they blow up and then repower, or overhaul, but there 1997's so this seems like a poor investment. My engine room is really tight and its difficult to get at lower components and this job is going to be a mother.
 
You can use hydrocarbon test strips (in the coolant) to see if compression gasses are leaking into the closed cooling system.

I’d also suggest having a cylinder leak-down test performed before pulling anything apart!

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Thanks,

Compression report:

Port: #4 165
Port :#3 170
Port: #5 180

Coolant was observed in the crankcase moisture venting, the coolant level was very low before they fixed the recovery tank hose.

Head gasket seals ? Didnt do a leak down due to restricted access.
 
Blackfin27 said:
Thanks,

Compression report:

Port: #4 165
Port :#3 170
Port: #5 180

Coolant was observed in the crankcase moisture venting, the coolant level was very low before they fixed the recovery tank hose.

Head gasket seals ? Didnt do a leak down due to restricted access.
Click to expand...


The cylinder leak-down test would have indicated where the suspect area was.
Unfortunately, once the cylinder heads have been removed, this valuable information is no longer available.


As for the cylinder pressures.......... the #5 cylinder @ 180 psi is excessive, and typically indicates an improper engine build (i.e., incorrect piston profile and/or cylinder head combustion chamber volume)!
 
from:
Blackfin27 said:
"port engine crankcase is venting moisture".

Same engine has some lower compression readings on #3,4,5.


to

coolat was observed in the crankcase moisture venting
&
Port: #4 165
Port :#3 170
Port: #5 180
Click to expand...

I'm a bit confused....how was the determination of coolant being in the crankcase discharge made? And like Rick observed, how is the compression low on 3,4 & 5?
 
makomark said:
............................
And like Rick observed, how is the compression low on 3,4 & 5?
Click to expand...

Mark, although this deviates from the original question, I was a bit more concerned with the high reading for #5 cylinder (180 psi).
Plus, the OP says; ""Same engine has some lower compression readings on #3,4,5. "

If #3, #4 and #5 are lower readings, I am curious as to what the other cylinder readings are! :eek:

I would expect that a typical 1997 350 Marine build would show numbers at/around 165 psi..... hence my comment re; incorrect piston profile and/or combustion chamber volume!




Blackfin, when you do tear this engine down, please post a few photos of the piston decks, and post the cylinder head casting numbers!





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Last edited:
RicardoMarine said:
Mark, although this deviates from the original question, I was a bit more concerned with the high reading for #5 cylinder (180 psi).
Plus, the OP says; ""Same engine has some lower compression readings on #3,4,5. "

If #3, #4 and #5 are lower readings, I am curious as to what the other cylinder readings are! :eek:

I would expect that a typical 1997 350 Marine build would show numbers at/around 165 psi..... hence my comment re; incorrect piston profile and/or combustion chamber volume!




Blackfin, when you do tear this engine down, please post a few photos of the piston decks, and post the cylinder head casting numbers!





.
Click to expand...

So my tech basically was suggesting run them for now, the tear down is a challenge due to really tough access conditions. He was concerned about the compression, but, I was thinking low side of range, not high?

They run pretty good. I was wondering if the compression rates would be linked to coolant moisture venting?

Fingers crossed I am hoping to get through the summer season without doing any further invasive work. Access for even the leak down on the crankcase is really tight.

Im headed to a repower....any thoughts on motor mount locations on my 1997 350 and a new 5.7 Captains Choice? Similar?
 
I'm baffled again....if one has adequate access to execute a compression test, then a leakdown test shouldn't represent any increase in difficulty.

Good luck with your repower....and the mount locations shouldn't be an issue...
 
makomark said:
I'm baffled again....if one has adequate access to execute a compression test, then a leakdown test shouldn't represent any increase in difficulty.
Click to expand...

I fully agree with Mark!

Also, I am still a bit curious as to the #5’s 180 psi cylinder pressure reading!



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Could the #5 reading be due to carbon buildup? 165# to 170# for a small block sounds normal. Maybe a decarb process would yield some different readings.
 
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