S40 T4 1998 Smoke Issue

[Greecey]

I have a 1998 S40 T4 which is an absolutely superb beast. She never lets me down and runs like a dream although she has high mileage. She has been regularly serviced and starts on the button every time.
For a while now I have started developing a smoke issue which smells like burning oil.
When I start her up from cold or warm / hot, she is smoke free, however, when she has run for a while and warmed up, when I pull up to a standstill and she settles to tickover, she has started puffing out smoke at intervals.
When I pull away agin, she clears. Further to this, when she has been running for a while, at steady 30 / 40 mph driving, if you back off the revs, she puffs out smoke again then after a further period, at these speeds, if you start to accelarate hard agin, she then sends a cloud out which clears after about 50 yards.
If you rev her hard agin, she clears and it starts all over again. then she puffs out small clouds at intervals when ticking over.
I have cleaned out the oil return pipe, and she has been regularly and well serviced with good oil.
As she starts from cold / standing ok I am of the belief it is less likely to be the oil stem seals. Could I be right in assuming it is the turbo?? I have been advised that as it happens in differing ways, it is most likely the turbo as opposed to piston rings??
Any help / advice would be gratefully received as she is a great car and I want to sort her out however, as everyone is, I am on a tight budget.

[960kg]

......how many miles has the engine completed?.........as you have written the problems, IMO it is the valve stems worn and / or oil stem seals......when cold starting, although the oil would have seeped passed the valve stems when stopped the amount burnt would be small due to the cold and thicker oil so not much smoke just normal cold start smoke.......when on a trailing throttle the depressions in the inlet tract are that strong that unless the valve stems and seal are in good condition it will draw oil passed them to be burnt.....it will be different to piston rings gone as it would smoke on WOT as well because the pistons act as a pump.......because of the necessary work involved why not do a compression test to see if the valves are seated ok as these T4`s run on 95ron can burn out the valves and put excess coke on the side of the throat of the exhaust valve causing some sideways pressure which would cause extra wear on the guides.........also give the inter cooler a clean out as some people complain of oil resting in the bottom of it after a turbo blown up and it has not been cleaned out........you could try a different oil such as Castrol Magnatec 10W 40 unless you already use it of course.....Good Luck

[Greecey]

Many thanks for the reply.
The car has covered 150K which I know is quite high, but having had a 360 which covered well past that without any major work and an 850 with 200K + I know they can handle it.I was intending to clean through the intercooler and change the turbo as a first option but not sure whether it would be worth stripping the head first??

[gmain1967]

Sounds like a tired engine, possibly in keeping with the miles unfortunately. However, given the likely costs involved, why not try something like this?

http://www.forteuk.co.uk/product.php.../Oil_Fortifier

A few folks on the forum have used the conditioner that is meant to help with worn seals causing oil leaks, with good success, so possibly worth a go? Even if it does work though, probably a delay of the inevitable....

Best of luck