adding a PCV valve, possible drawbacks?

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gadget73

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I'm considering adding PCV valves (one per motor) to my 93 MerCruiser 5.7L/Bravo engines. I have a vacuum port on the intake currently sealed up with a pipe plug, so the plumbing is not an issue. Would there be any drawback to adding a PCV system that I'm not anticipating?
 
Mkos1980

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Re: adding a PCV valve, possible drawbacks?

If your thinking about the pipe plug behind the carb to the left, forget about it. That port is for a brake booster in an auto application which pulls vacume but not consistanly. If you run a line to that port, number 8 will run very lean. You need to modify your carb so that you can accept one there. Not the intake manifold.
 
JustJason

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Re: adding a PCV valve, possible drawbacks?

Uhmm... what are ya looking to do here beside maybe being green, which isn't a bad thing in itself. PCV valves are part of emission controlls systems in automobiles that do not apply to boats.

oh yeah... and it wouldn't plumb into the intake... it would plumb into the valve covers and vent into the top of the carb. You can always replace your breather tubes with pcv's if you feel like saving the planet 1 man at a time.
 
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Rat Capri

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Re: adding a PCV valve, possible drawbacks?

PCV systems are always a good idea on ICE's...cleaner oil, positive oil pressure control and better ring sealing....if you have the know how I would recommend it....my .02
 
Mkos1980

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Re: adding a PCV valve, possible drawbacks?

My Edelbrock Marine carb came with no fittings, but I drilled out the "semi" drilled port where one would be on the Edelbrock automotive carb and screwed in a fitting. Works perfect!
 
Evinrude Boater

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Re: adding a PCV valve, possible drawbacks?

I installed pcv valves in my valve covers like JustJason suggested. Without the vacuum it pressurized the engine so much it blew out one pcv valve and the dip stick. Not fun cleaning up all that oil in the bilge. Merc designers would have put them in if they were necessary. Learn from others that have been to school on that issue.
 
Mkos1980

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Re: adding a PCV valve, possible drawbacks?

You should never have 2 pcv valves. One side should be a breather, one side the valve. No wonder you blew one out EB. If you look at any auto engine they only have one pcv valve and 1 breather.
 
Mkos1980

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Re: adding a PCV valve, possible drawbacks?

Evinrude Boater said:
Merc designers would have put them in if they were necessary. Learn from others that have been to school on that issue.
Click to expand...


Merc now uses PCV valves on all their engines carb'ed and EFI'ed
 
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Rat Capri

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Re: adding a PCV valve, possible drawbacks?

Evinrude Boater said:
I installed pcv valves in my valve covers like JustJason suggested. Without the vacuum it pressurized the engine so much it blew out one pcv valve and the dip stick. Not fun cleaning up all that oil in the bilge. Merc designers would have put them in if they were necessary. Learn from others that have been to school on that issue.
Click to expand...

installation error, only need 1 pcv valve and a fresh air inlet ( breather or tap off air inlet)
 
Evinrude Boater

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Re: adding a PCV valve, possible drawbacks?

Rat Capri said:
installation error, only need 1 pcv valve and a fresh air inlet ( breather or tap off air inlet)
Click to expand...

The elbow part number is 97850, what's the pcv valve part number? I can't find one for my 1987 4.3.
 
bruceb58

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Re: adding a PCV valve, possible drawbacks?

My question is WHY? Engines work fine without them! If you have excessive blowby, that is a sepearate issue.
 
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gadget73

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Re: adding a PCV valve, possible drawbacks?

JustJason said:
Uhmm... what are ya looking to do here beside maybe being green, which isn't a bad thing in itself. PCV valves are part of emission controlls systems in automobiles that do not apply to boats.

oh yeah... and it wouldn't plumb into the intake... it would plumb into the valve covers and vent into the top of the carb. You can always replace your breather tubes with pcv's if you feel like saving the planet 1 man at a time.
Click to expand...

Goal is to get rid of the oil smell in the cabin. I figure if I burn the oil fumes instead of having them aimed in the general direction of the flame arrestor, it might help a bit. I also don't like the combustion byproducts hanging around in the crankcase. The actual emissions bit I'm not concerned with. I'm not real convinced that adding a PCV alone would affect all that much, and I have no illusions that adding one is going to save the world, especially considering the fuel burn and the 30 year out of date engine technology in use on your typical marine motor.

Of course, I also assume that the new motor with no oil leaks is going to go a really long way towards fixing the oil smell, but I was thinking if I could spend 15 bucks in parts and a half hour of my time to completely eliminate it, it wouldn't be a bad thing.
 
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Ridemywideglide

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Re: adding a PCV valve, possible drawbacks?

PCV valve or not, oil fumes will come out those hoses...

Just plumb them into the flame arrestor and skip the valves..
 
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KJSmitty

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Re: adding a PCV valve, possible drawbacks?

gadget73 said:
I'm considering adding PCV valves (one per motor) to my 93 MerCruiser 5.7L/Bravo engines. I have a vacuum port on the intake currently sealed up with a pipe plug, so the plumbing is not an issue. Would there be any drawback to adding a PCV system that I'm not anticipating?
Click to expand...

Gadget,

I have a 2003 5.7 and it has the breather tube coming from the starboard valve cover and the PCV on the port side valve cover (both to the rear of the covers).

You must have the breather tube that goes up to the flame arrestor - that's the "vent" side of the system. For the PCV valve itself: Near any 90s or later Chevy V8 PCV valve will work.

ALSO, you should actually use manifold vacuum - direct from the manifold is very typical but if the source is dependent/specifically on one intake runner then you would want to use something near the center/carb base area etc. Something off the carb is fine as well,,, but ensure it's a very large source and absolutely not a "ported" vacuum source. IE: effected by throttle position.


Good luck
 
JustJason

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Re: adding a PCV valve, possible drawbacks?

Goal is to get rid of the oil smell in the cabin.
Click to expand...

Okay... now that I know what your doing... Yes adding pcv valves may actually help your situation. I'm surprised you are having odor issues though with just the breathers.
Either way... if you have 2 breather tubes (1 in each valve cover) Replace both of those with pcv valves and aim the hoses as close as ya can to the flame arrestor. Don't listen to these monkeys who are telling you to grab intake vacuum. All thats going to do is creat an air leak and cause your engine to run terrible and probably not idle. Your on the right track here. Should take you all of 2 minutes once you get the valves. You may want to pull a breather tube out before you go to the autoparts store (i would go to a NAPA personally) just to make sure that the valve cover side and the hose side are the correct dimensions.
Good luck.
 
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Rat Capri

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Re: adding a PCV valve, possible drawbacks?

bruceb58 said:
Doesn't matter in a marine environment. that is why you don't have air filters.
Click to expand...

oil doesnt get "dirty" by particulate contamintaion alone

bruceb58 said:
Has nothing to do with oil pressure.
Click to expand...

yes it does, breather pressure negatively affects oil pump effeciency

bruceb58 said:
Please explain this one!
Click to expand...

rings will seal better if they're not fighting crankcase pressure
 
bruceb58

bruceb58

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Re: adding a PCV valve, possible drawbacks?

Rat Capri, can you show us a picture of your PCV set up? You do have one right?

I guess I was expecting an actual explanation of other than " I said so". I would really like to see a boat engine's oil contamination level increased to a point that it would really contribute to extra wear or failure of an engine. Most boat engines fail for a variety of reasons and would not be because of extra contamination due to not having a PCV valve.

The PCV is essentially a pollution control device. It also requires some mintenance to make sure it is clean. I guess I subscribe to the philosophy of why complicate things more than they already are. So now when things are running rough or your running extra lean because of a leak, you have to add in the possibility that it's a PCV valve? There are enough things that require maintenance on a boat without adding an additional item...and that is my $0.02.

When your boat runs lean because you have a leak in your PCV valve hose and you burn the top of your piston off...we told you so.

Rat Capri, can you show us a picture of your PCV set up. I am sure you must have one since they sound so beneficial.
 
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