crankcase breathers

you cannot relpace the PCV with a breather they are not the same and do not perform the same function. You should have a breather on one and a PCV on the other valve cover.

Chris:

Question: Couldn't you use two breathers and be ok? Seems I have seen setups like this on the older boats.

They way I see it, the breather works at high vacuum conditions (i.e. idle and small throttle applications). The PCV comes into play at large throttle applications to help evacuate the crankcase during periods of maximum blowby or crankcase pressurization.

I do tend to think that one breather could get overwhelmed (especially on older engine) with the result of excessive pressurization of the crankcase.

Just my thoughts.

Brian,

I asked the same question a few weeks ago for the same reason. similar thread(with pictures)

Some speculated there must be a pcv valve within one or both of the fittings for the hoses from the covers. They were both just breathers. My boat (76 chevy 305)did not appear to have any pcv valve. I know there are external pcv valves but I don't have one. So as to not take any chances on mucking things up, I found valve covers with the same hole configuration as my orginals. Post before and after pictures of the engine face lift. Curious to compare since we are both using the fall to tinker with our boats in the same way.

bmiller you can run either type, all the mercruisers have used a breather type ,hoses vented to the flame arrester, for years, contrare to 79,pcv, positive crankcase ventalation,is to remove the hydrocarbons that would have been vented to the atmospere. this was the first of emmision control devices.as a secondary result of this "sucking action" you got less "weeping" or "blowby" from the valve covers and dipstick.if you have a motor with a lot of hours leave the PVC system intact, a new engine or low hour will do just fine with twin breather tubes(mercruiser still uses this).my new 331 stroker has no blowby and uses the two hose system,go to my link and i think you can see how i did mine....... boat dr

and as far as removing moisture from the motor,my quetion to 79 would be where did it come from,and i dont have this problem.

The condensation is a result of the combustion process. Water (very small amounts) is a byproduct of burning gasoline.

TRBenj wrote: The condensation is a result of the combustion process. Water (very small amounts) is a byproduct of burning gasoline.

that would be hydrocarbons

or unburnt gasoline during the combustion process,

if there was water present it would instantly turn to steam and be pumped out the exhaust.

Oh crude, I disagree with Brian again. The moisture in the engine will get out simply by evaporation via a crankcase breather. Here is blurb on the PCV valve:

Description: The crankcase ventilation system, often called positive crankcase ventilation (PCV), consists of a PCV valve or metered orifice (calibrated opening), its vacuum hose or line, a supply hose providing air into the crankcase, and on some applications, a breather filter to clean the air provided to the supply hose.


Purpose: The purpose of the PCV valve is to regulate the flow of crankcase fumes into the intake manifold where they can be burned. Prior to 1963, cars had no PCV and used road draft tubes that just left the hydrocarbon emissions from the crankcase out into the open air. The PCV valve also has a secondary role as a check valve, to prevent flow back into the crankcase. This prevents potential ignition of the crankcase fumes, should the engine backfire. The PCV system is also crucial for to proper engine sealing. The system alleviates crankcase pressure, which can push out on seals and gaskets, contributing to oil leaks.

Here is a good PDF describing the PCV system:

Crankcase ventilation