pcv system

D

d-reed

Member
Oct 23, 2018
53
Western Ma.
Boat Info
1996 Sundancer 250 DA
Engines
Gen 6 454 carb Bravo 1
So I have a question about my PCV system in my 96 Sundancer. I know that on a car the hoses from the PCV valves run to a port on the carb or intake manifold. Why does a boat engine run the hoses to the Spark Arrestor and not to a vacuum port? The reason I am asking is because I have very slight blow bye from the PCV hoses and at times when run hard I get some oil smell from the engine compartment. I have a Carter AFB that does not have provision for vacuum lines.

I was thinking of hooking the PCV up to the port on the intake manifold to help remove the vapors more efficiently. Any thoughts on this?

Thank you
 
If your hose goes to the arrester then you don't have a pcv, it's just a vent. If you add one, you will create a vacuum leak and will have to tune around that. If you have excessive blowby a pcv will vacuum the oil out of your engine quickly.
 
And foul the spark plugs, create a possible no start and an expensive tow. A short cut is the longest distance between two points.
 
I would look more towards an oil catch can as the temporary fix...
 
scoflaw said:
If your hose goes to the arrester then you don't have a pcv, it's just a vent. If you add one, you will create a vacuum leak and will have to tune around that. If you have excessive blowby a pcv will vacuum the oil out of your engine quickly.
Click to expand...
These are not just hollow elbows with a hole and a hose attached, they have a check valve in them. I guess I will look and see if its supposed to have pcv valves or just hollow fittings? Not sure.

Engine is still new even though its been run on a Dyno and I have put about 30 hours on it. I would say the amount of blow bye is way less than a burning cigarette. I have 150-155 psi of compression in all the holes so Im not to worried about it to be honest. Pretty much just wondering is all. thanks
 
scoflaw said:
If your hose goes to the arrester then you don't have a pcv, it's just a vent. If you add one, you will create a vacuum leak and will have to tune around that. If you have excessive blowby a pcv will vacuum the oil out of your engine quickly.
Click to expand...
The PCV Valve will not drain your engine oil unless there is something wrong with it. At Idle vacuum is very high, 16-20 in. The PCV acts as a buffer against oil being drawn from the engine and regulates vacuum applied to the engine based on load. The check valve and spring in the valve moves to different positions depending on load and speed and does not suck up oil. UNLESS, like I said, it is broken.
I know that around 2011, Chevys had a PCV issue. The system had a design flaw and would allow oil to be drawn from the engine, that oil was causing the rings to stick and therefore causing blow- bye and even more loss of oil via the sticking piston rings from all the excessive oil being burned. They came out with an updated valve cover with a new baffle design that dramatically lowered oil consumption.
 
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Blowby is oil in vapor form. A pcv will suck it up like a vacuum cleaner.

I've done my share of pcv experimenting, your turn now
 
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As stated earlier, if the blow by is less than the smoke from a cigarette then the intake of air at the spark arrester should be more than sufficient to consume the blow by. The smell you detect may be due to the engine burning paints and sealants associated with is newness. Or possibly a a small oil leak not yet detected.
 
A couple more thoughts, check the valve cover gaskets. The highest volume of oil is present in the top end of the engine at high rpms and may leak on the lower sides of the covers dripping down and burning once it hits the exhaust ports.
May be the valve stem seals too. At higher rpms with more oil present around the valve stems the oil may be sucked into the combustion chamber giving the exhaust an oil smell and the exhaust can back flow into the cockpit due to the “tailgate “ effect.
That’s all I have.
 
I appreciate everyone's input on this. I will monitor things this weekend. I looked things over yesterday, no leaks that I can see or feel. Very Very hard to see things in this boat due to it being a big block, batteries, holding tanks, and hot water heater and so on. Like I said I only have 30 hours on this thing so I'm sure it will seal up a little more as time goes on. The oil level has not gone down at all so that's a good thing.

Thanks again!
 
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