PCV oil consumption

[Rob123]

Mk3 engine is consuming oil - slowly, but too quickly to confidently set off on RBRR. It's not the valve guides as they have been recently replaced and there is no signs of oil leaking elsewhere. I'm suspecting the PCV valve, or should that be PC Valve?

The valve trap seems to have a large amount of oil in it. See pic. Is this normal? I would have thought this should run back into the rocker cover if it is oil and not oil fumes but that would rely on a downhill path of which there isn't.

Any comments?

[Clive]

As a test, you could block off the inlet to the valve (bolt in the rubber pipe is ideal) and run the rocker breather to a catch tank (again, almost anything works, plastic drinks bottle, coke can etc etc or in my case £1 small aluminium drinks bottle from the poundshop)

That will tell you how much oil is coming out the breather.
Other reason could be rings. Any blue smoke out the exhaust? probably needs a following car to watch, ideally under hard acceleration to high rpm, and a bit later lift at high rpm and see if you get smoke on overrun.

Finally, how much oil are we talking about? pint every few hundred miles?

[Hogie]

Hi Rob,
          I run  a TR4A and have had the same problem.
To isolate the PCV I simply blanked off the intake pipe and had the rocker outlet run through  a longish pipe down towards the ground.
The first thing I noticed was that there was NO air or oil coming out of the pipe - held hand near the open end and nothing.
After a good number of miles (100=) there was no oil on the engine bay body work where the pipe outlet was immediately in contact  with.

This suggested there was no excessive crankcase pressure (blow by etc)

The oil consumption went from 300miles/ltr to inexcess of 600miles/ltr and counting.

It is possible for the PCV to malfunction, continuous sucking or no suck. One uses a great deal of oil the can cause serious leaking from any hole in the engine block.

I'm now running with a cheap catch tank from ebay. The tank is empty after 1000+ miles.

There is one thing to look for in the PCV  - it must be positioned so that the  pipe from the rocker is sloping downwards so that oil can run back into the rocker cover pipe. Other wise it will drain into the manifold.

If you are burning excess oil in the combustion have you noticed 'pinking'. The oil reduces the RON of the fuel.
I had bad pinking - couldn't get rid of it. It was the oil.

Roger

[Matt306]

Dont discount worn valve guides.  I had a head done under 3000 miles later i had low compression. A valve guide was worn oval for some reason.  Check the rockers are free to move on the shaft.

[Rob123]

Thanks for the advice, will be rigging up a collector and blocking up the valve and reporting back. It may take a while.