|
| Author |
Message |
    
Edward G
Visitor
| | Posted on Thursday, November 08, 2007 - 05:12 am: | 
|
Background.
Twin KAMD42- 230hp shaft drive
- 1300hrs total, 700hrs following full rebuild
- Never had trouble with excessive oil consumption before.
- Oil level checked before each cruise.
Incident 1
- the owner did around 7 hrs of cruising during a recent weekend (most of it at 3400 rpm) and did not notice anything unusual (e.g. black smoke or oil residue in water)
- however, boat felt a little sluggish
- later checked oil level again, dipstick did not show any oil, i.e. oil level had dropped drastically. Oil check was left 10 min after stopping the engine, to let the oil drain to the sump.
- subsequent manual extraction of remaining oil suggested that we had lost around 5 litres during that weekend trip!
- since there was no oil in the bilge, we concluded that it must have gone out the exhaust
- however, with 5 litres missing, should we not have seen black smoke and or oil film behind the boat???
- there was a suggestion that a small leak in the oil cooler could account for losing oil on a run, without a trace (simply gets washed out).There was no sign of oil on the surface of the water from the exhaust, at startup or high idle.
Incident 2
- an experienced Volvo mechanic did a sea trial
- when running at 3200 rpm, oil was coming up the filler pipe, spilling out when he opened it - but still no black smoke or oil residue in water via exhaust
- when pushing to full revs at 3800 rpm, oil squirted up the dipstick shaft in volume - but still no black smoke (note: during weekend trip the engine was never run at full revs, which explains why there was no oil in bilge)
- the mechanic's diagnosis: piston rings or bore is damaged. Excessive blowby can be seen, causing a buildup of sump pressure (due to inadequate breathing capacity), which supports this theory
In summary: it appears we have got two possible explanations for oil loss:
a. heat exchanger leak - explains oil loss without a trace (Incident 1), but does not explain why oil squirts out of engine at high revs into the bilge (Incident 2)
b. rings/bore – the evidence of blowby explains why oil comes out of engine into the bilge, but does not explain why there is no black smoke via exhaust, or nor does it explain the missing 5 litres of oil from Incident 1 above.
I should add that whilst the engine crankcase breather has been redirected away from the air filter into a ‘sludge’ bottle, the actual diameter of the breather hose is original standard. Hence with the higher blowby, breathing becomes inadequate, causing crankcase pressure buildup.
Dealing with the piston rings is obviously going to be very expensive, with the removal of an engine and full strip down.
The big concern though is that there seems to be no common explanation or both oil losses. How can you loose 5 litres of oil without trace, in particular?
Anyone with any thoughts or experience with this issue? |
Hesfu1952
Visitor
| | Posted on Wednesday, December 12, 2007 - 11:55 am: |
|
"causing crankcase pressure buildup"
I had similiar piston, rings and cylinder defect in my KAD42P, (1996, 750 hours) was about 2 gallons in a few seconds.
The preceding reason were false injectors. |
|
|
