Crankcase pressure

Colin K

Colin K

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Hello,
Just had a fantastic trip from Ipswich "home port" to Southwold where we had a great 4 days. We tried to get out yesterday and got half way to Orford when it blew and we more resembled a U boat in mid Atlantic so we turned back running back into Southwold where the old tub is staying for a week.
During the battering I checked the engine to see how she was doing and found that the crankcase pressure was high and throwing a bit of oil out too. The cap has a wire guaze and holes around the neck so it was hard to direct it in a particular direction but some was being sucked back into the air intake.
The engine is a Watermota Sea Panther which runs mechanically as sweet as a nut so Im hoping a broken ring is not to blame ! No rattles, no loss of power or misfiring no oil used.
Servicing prior to our trip I did a full service and had real difficulty bleeding the fuel system but cured it by renewing nearly everything and found a cracked CRV filter top. Changed the oil which is where I wonder if anyone could advise me. A mechanic told me to use a certain brand of oil which I questioned as it was 15/40 "thinner" than I had used before. I would normally use 20/50 mineral oil as the engine is circ late 1960's ! I am wondering if the thinner oil is getting past the rings and causing the blow back/crankcase pressure. When I return later next week im going to change it anyway I think but curious if anyone had any experience here.

Thanks for any help. Colin.
 
The service manual http://www.bluemoment.com/manuals/Watermota Sea Panther MkII service manual.pdf describes the engine ventillation system as " a semi-closed positive ventillation system with a breather in the filler cap and an oil separator close to the fuel pump.

I guess that means the engine should be drawing the oil fumes out via the oil separator into the inlet manifold or air intake, fresh air entering through the filler cap.

Check the oil separator and associated hoses. It may well incorporate a wire mesh flame trap which is in need of cleaning or a crankcase emission control valve which requires servicing.
 
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Yup- sounds like the oil. We had the same sort of trouble with a modern lightweight oil in our Yanmar.

I gave it an old fashioned look and a bit of thought and went to Morris Golden Film 20/50.

This is suitable for both petrol and non turbo diesels and works well for our three cylinder Yanmar with in excess of 3,000 hours on it. I have not needed to top it up between its annual change since using it.

At under £20 for 5 litres its worth a shot.

Good Luck.
 
Hello,
Thanks for the replies, yes the oil breather/flame trap is a little box with a baffle in it and thats all clear. The top of this goes up to the air cleaner which has a wire gauze in it. She has always had a little bit of positive pressure from the cap but not as much as since i did my last service when I fed her the thinner oil.
Giving me a little hope is the fact that the pressure is not to bad at first fire up but gets worse as the engine gets warm so I'm kind of hoping that this is the oil thinning as it gets hot ???

Thanks again. Colin.
 
If the engine, was working harder, for longer period and at higher rpm than normal, then you would expect more pressure passing through the pistons and therefore through the oil filler/cap. When the cap is off at idling and the engine is cold you should get little air/pressure through the cap; could be natural wear/tear and well worn piston rings. If the engine does not use oil then you don't really have a problem.

When it comes to oil, my view differs from the majority of the forumites; I use synthetic oil on my original 1970's Volvo, which it has the benefit of remaining stable at various temperatures and conditions.
 
When it comes to oil, I agree with you, the difference between 15/40 and 20/50 is not a lot atall. Synthetics and semi's are excellent "oils".
 
Modern oils are 'thin film' types designed for the close toerances of modern engines and are not suitable for old engines. The rule for choosing oil type is to use what was available when the engine was new.
 
I agree. Modern oils are for modern engines. For instance some very modern oils are not suitable for flat tappet engines (old OHC engines like Jags, Imps and Alfas).
If the "problem" occurred since the oil change, revert and review the situation.

Old engines tend not to have to contend with high temperatures like modern engines so wide range multi-grades are not so important.
 
ccscott49 said:
When it comes to oil, I agree with you, the difference between 15/40 and 20/50 is not a lot atall. Synthetics and semi's are excellent "oils".
Click to expand...

I totaly agree-but not for old technology engines made with larger clearances and often poorer cooling. When I was racing 12,000 RPM 100 BHP motorcycles in the '70's hi-tec synthetic boosted oils were needed to keep it all together.

But in my time as a classic, vintage and veteran motorcycle dealer I came across many instances of customers experiencing problems with lightweight modern oils. When they used monograde 40's and 50's or 20/50's with engines with plain bearing these issues went away.

Horses for courses.

IIRC the OP had no problems before the lighter oil was used..........................
 
Hello all,
Thanks everyone for your help. I think a thicker oil has a chance of curing my problem the Cox site suggests give it the oil that was around at the time and thats good basic advice. I hope !!!
So its to the boat on Thursday a quick oil change and sail back to Ipswich in this weather window promised.
Mind being stuck in Southwold is not all bad !!
Once again thanks for all the help.
Colin.
 
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