Peugeot RCZ Sport - Smoke on start up and revving at lower gears. 130k miles.

Hi there, I have a Peugeot RCZ 2010 Sport.

It smokes a small amount on start-up and a bit more while at lower gears and higher revs. This has became more prevalent since switching to 0w30. The car is at 130k miles.

The car burns a decent amount of oil.

Everything so far has pointed me towards the valve stem seals but the smoke isn't blue whatsoever it's more so white and lingers a bit, secondly the job has been quoted at £2,000+

The car struggled to get through it's Emissions on it's previous MOT (if this helps anyone)

It managed to pass by being held at the lowest possible rpm in the fast idle test (2588rpm) 2500rpm-3000rpm.

Fast Idle Test:
CO: Max 0.20% - 0.20%
HC: Max 200ppm - 28ppm
Lambda: 0.97-1.03 - 0.99

Natural Idle Test:
689rpm
CO: Max 0.30% - 0.29%

I replaced the upstream O2/Lambda sensor with a Bosch OEM part, but I think the downstream still has a non OEM part.

Does anyone have any insights or suggestions that AI or research might not have considered? The valve stem seal job is not economically viable.

Secondly, it has been recommended to use 5w40 on this car when it reaches higher mileage. Should I switch it asap?

There is an alternative method to replace stem seals with a special tool that allows to compress the valve springs and swap the seals without removing the entire head. It is much cheaper than traditional/official method offered at Peugeot dealership. Try to find independent Peugeot/Mini specialist who knows this stuff. Also, at this milage you probably should switch to another oil. I had similar issue (big white clouds after idling) and switching from 0w30 to 5w30 helped a bit. Maybe 5w40 works even better at your milage.

If, after idling for a while, you rev the engine and smoke comes out, it means the valve stem seals are bad or there are leaks from the piston rings.

Water vapor coming out when starting from cold is normal; it's condensation in the exhaust pipe.

You can also remove the spark plugs and inspect the porcelain tip. If it's oily and black, there's a significant problem with the oil.

You could also perform a compression test to check the condition of the cylinders and pistons.