PCV Valve and fitting a Catch Can

Having now been under the bonnets of quite a few PT's , I have noticed that some cars have an oil leak around the PCV (Positive Crankcase Ventilation) valve. So I did a bit of research on this system to find the cause, fix it and possibly improve on it

All engines, even brand new ones, “breath” that is some of the combustion gasses get pass the piston rings/valve seals and enter the crankcase. That’s part of what turns your oil black and breaks it down and that’s why you do regular oil changes….. You do don’t you !!

In the “good old days” the crankcase gasses and vapours were vented to the atmosphere via the oil filler cap or a breather/filter, containing an oil trap, which you then washed when the car was serviced.

Today with all the emission rules and regulations this is now banned. So this dirty air is vented via the PCV valve back into the air inlet to be burnt by the engine. The problem with this is that this dirty air is low in oxygen and high in oil and other vapours which are not idea for a “good clean burn” so the cars computer will sense this and alter the fuelling and timing to maintain an acceptable burn, at the cost of power and fuel economy.

So I decided to improve on this.

First of all I removed the PCV valve to sort out the leak and check if it was working correctly. The sealant around the threads was found to have gone brittle (this was the cause of the leak) The PCV valve itself was replaced as in the workshop manual says it can not be cleaned or repaired, but unless the spring has broken inside I can’t see why it just can’t be cleaned with carb/choke cleaner, then checked by sucking and blowing though it (a PCV valve is basically a one way valve) The new valve was fitted using PTFE tape around the threads for a better seal

I then bought a second-hand catch tank from……………you guessed it eBay

The tank consisted of an aluminium container with an inlet and outlet connection, a fill level indicator and a drain plug. As the tank had a removable top, I added an internal vertical divider, with a number of holes drilled in it and filled the two sections with wire wool sprayed with K&N air filter oil. The idea being to force the dirty gasses through wire wool and trapping the most contaminates as possible.

The tank was positioned at the rear of the airbox, partially because it’s away from the engine, so a little cooler, the idea here is that any water in the dirty air may condense out and cooler air is better for the engine (more power) plus it looked good in this position

I then piped the tank in using breather/vacuum pipe. The pipe runs from the PCV valve to the catch tank, from the catch tank to the inlet.


The system was run for a couple of weeks and I then checked the inlet and outlet pipes (the inlet was wet and the outlet dry) it’s working. I couldn't, and didn’t expect to feel any difference with engine but cleaning this intake air must be good for the engine and if the engine can sense the difference, the fuelling and timing will be adjusted, for the better.


Parts Required

New PCV valve (optional)

Catch tank

1 metre of breather hose

3 or 4 cable ties

Air filter oil (optional)

PTFE tape

UB40 !!! ( helps when pushing the hoses on)


engine 2

Red Catch Can fitted behind the Air Box