how often should you change these?

According to my 78 owners manual every 30000 miles or 24 months which is the same interval they give for the carbon cannister filter.

ok, what is it for? ive had my car for over a year. dontthink ive put nearlky 15k on it this year. maybe more like 6k-9k TOPS

I found a reference in the FSM on how to check if it's still working or not...

"With engine running at idle, remove the ventilator hose from the P.C.V. valve. If the valve is working, a hissing noise will be heard as air passes through the valve and a strong vacuum should be felt immediately when a finger is placed over valve inlet." Makes reference to changing the P.C.V in accordance with the maintenance schedule. Anyone with a 75 owners manual out there...Huh Huh...

webdawg1

Short description of what it does: Returns blow-by gas to both the intake manifold and throttle chamber under various throttle conditions. (I.E. -Burns the returned gas reducing emissions)

webdawg1

Quote from the service manual:

The PCV system, used on all models, routes crankcase fumes into the combustion chambers for burning.

Fresh air drawn from the air cleaner housing scavenges emissions (e.g., piston blow-by) from the crankcase, then the intake manifold vacuum draws emissions into the intake manifold. They can then be reburned in the normal combustion process.

curse you! where did you get a color guide? mines all black and white....

curse you! where did you get a color guide? mines all black and white....

That's from Clymer's Datsun 810 1977-1980 service manual. It has a lot of nice charts and diagrams but when it comes down to information, I'll take the FSM over any of them.

It's a $4 part and a 2 minute fix. If you are unsure of it's condition just change it real quick......