Chuffing 'vapour' out the filler cap

My 19j 'chuffs' out 'vapour' out of the filler cap hose that then goes into the air intake.
I am aware that this is a sign of a TD on its way out (or is it?) and I have disconnected it from the air intake, as I have been told that it sometimes feeds itself oil and then you gotta problem and stalling is the only option to stop it.
My question is.. why does it 'chuff' out smoke/vapour?
Is it worn piston rings?, or is it just, when the oil warms up it just releases 'vapour'?
do I needed to worry to much?
Will it last at least 10000 miles? least give me time to find a 200*
I was given a 'red folder' when I bought the 90 and it had receipts in it listing new pistons and rebuilt in 2003, clock says 123000miles ish
and it sounds ok.
What is the 'vapour'?
What are the usual causes?

Phew long post, thanks in anticipation

first they all do it to some extent. Mine did for the 12months I had it as well as spraying oil out of the dipstick tube. and never failed to start & never broke down. & when I moved form Hull to soimerset it was loaded to the roof with all me earthly belongings and towed a 4berth caravan behind it. with no hassle at all.

Main cause is worn rings/bores. or blocked oil pickup in the sump or even blocked sump breather or oil filler cap

it'll run for 10000s of miles like that, just don't do much over 50mph in it, don't be surprised if the filler cap gets blown off coating the underneath of the bonnet with oil and carry plenty of oil with you

and start saving for a 200

Sean said:

it'll run for 10000s of miles like that, just don't do much over 50mph in it, don't be surprised if the filler cap gets blown off coating the underneath of the bonnet with oil and carry plenty of oil with you

and start saving for a 200

Click to expand...

Nah I regularly did 65/70 (eventually) in mine & filler cap dunt blow cos the pressure is released thru the breather pipe what yu extend & stick inside ya chassis Thus ensuring the o/s front chassis leg never corrodes as well.

redhand said:

Nah I regularly did 65/70 (eventually) in mine & filler cap dunt blow cos the pressure is released thru the breather pipe what yu extend & stick inside ya chassis Thus ensuring the o/s front chassis leg never corrodes as well.

Click to expand...

mine blew many times, had a little red light on the dash to warn me when it happened

i put a ickle oil collector on the end of the breather to collect the oil, which was poured back in when filling up with fuel

Brilliant guys. Thanks for your advise.
That makes me feel better, I am always saving for a 200
I am glad the TD aint as poo as people say
I will put that oil collector on, like that idea.
But equally like the idea of it coating my chassis
Maybe I could split the pipe and feed it into each side of my chassis, then that faster I go the more the chassis gets lubed.

mine was chuffing out the breather but iv just done a full head rebuild on it and reground the valves n did the valve seals, now it dont chuff at all. worth a look